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Measuring Crystal & IF Filter Frequencies

Arv Evans
 

开云体育

Hi

Hans' comments (see below) are very appropriate to the measurement of Crystal frequencies.? I too found that if you solder the crystals in place, it may be necessary to wait several minutes for things to cool down to where frequencies are stable.? This applies to crystals in the 10 mhz filter as well as those in oscillator positions.? When soldering the crystals in place, it helps to use a heat sink on the leads between the solder joint and the crystal.? Just gripping the lead with a pair of pliers while soldering is usually adequate.? Wrap a rubber-band around the pliers handles to keep them on the lead if you need three hands to hold the pliers, hold the solder, and hold the soldering iron.

If you build the AF section, the IF-to-AF mixer, and the BFO before you build the IF Filter it is possible to use these as part of your test equipment in alignment of the 10 mhz filter.? Build the VFO but temporarily replace the VFO resonant circuit with a spare 10 mhz crystal and a series variable capacitor.? Use this oscillator as the signal source to "test" your IF Filter.? When the "VFO Crystal" and the BFO are tuned you will find a zero-beat if they are both at the same frequency.? Tuning either of these oscillators off-frequency will result in an audio tone that represents the difference in frequency.?

Using a simple diode detector and high impedance voltmeter you should be able to plot the bandpass characteristics of your IF Filter (turn the BFO "OFF" for these measurements).? The ideal bandwidth of the filter would be about 2.1 KHZ wide at the -6 db points and 4.2 khz wide at -60 db.? You may not be able to achieve quite that good a response with the simple ladder filter used in the BITX series, but it is the goal to strive for.? The slope at the sides of your filter should be as steep as possible.?

Once you have a picture of your filter bandwidth you can adjust the BFO frequency to position it at the -20 db point on one side or the other of that pass-band.? Which side of the passband you use is determined by which sideband (USB or LSB) you wish to transmit.? Why put the carrier at the -20 db point...because that helps to attenuate some of the lower audio frequencies in the desired sideband.? These lower audio frequencies are not really necessary for intelligibility, but they do use up a significant amount of power if they are transmitted.? Filtering out the lower audio frequencies ( 0 hz to about 350 hz ) allows more of your transmitted power to represent only the audio spectrum that is necessary for communication.? This same characteristic helps improve the apparent quality of received signals by reducing received audio power that might be devoted to these lower and unnecessary frequencies.

ALTERNATIVE FILTER PLOTTING METHOD:
If you do not have a frequency counter for monitoring the 10 mhz signal source, there is an alternative method for plotting the bandwidth of your filter.? With the BFO "OFF", use the RF voltmeter arrangement and your tunable VFO Crystal oscillator to determine the center of your filter pass band.? Set the 10 mhz VFO crystal oscillator to the center of that bandwidth.? Now turn your BFO "ON" and adjust it for a zero-beat with the VFO crystal frequency.? Now comes the hard part!? Slowly adjust your VFO Crystal frequency to find the estimated 1000 hz tone location on both sides of this zero-beat.? Carefully mark those frequencies on the dial of your VFO Crystal tuning knob.? Now you can turn the BFO "OFF" and proceed to use your "calibrated" signal source (the VFO Crystal oscillator) to make an approximate plot of your IF Filter bandwidth.? Note, that this is only an approximate way to tune your filter, but it will get you close enough for most operations.? The signal level through the filter should decrease very rapidly as you tune beyond the 1 khz points ( +1 khz and -1khz represent a total of 2 khz and should be the approximate edges of your filter bandwidth).

The IF Filter is probably the most confusing part of the BITX design, but it is also the easiest to duplicate if you use exactly the same components that Farhan specified.? Departing from Farhan's design specifications is what seems to cause the most confusion and doubt.? My recommendation would to build at least one BITX20 that is exactly like Farhan's original design.? That exercise provides the necessary experience to support deviating from his design, and it will provide you with a reference transceiver that may be used for comparison type troubleshooting.

73's
Arv
_._

From:? Hans Summers <>
Date:? Wed?Jul?14,?2004? 2:38 am
Subject:? RE: [BITX20] CRYSTAL MEASUREMENTS

?
> Frequency reading is still moving / drifting,
> although circuit has been warming up about 5
> minutes.
> Q: How do you "note/catch" the frequency in this situation ?
?
Your circuit and method look Ok to me... how bad is the drift, and what happens if you wait longer than 5 minutes? The drift could also be in your frequency counter (or PC if you are using that as a frequency counter). The crystal itself will also drift, we tend to think of crystals as rock stable but they aren't at all. Relative to an LC oscillator maybe, but not in absolute terms. Just read about the problems I had getting a stable frequency in my 30m QRSS beacon (?and ).
?
In my BITX20 evaluation, I managed to find a socket which fit the crystals. If you are soldering the crystals in, you might find that the initial drift is rather high due to the crystal being so hot from the soldering iron and needing to cool back down to room temperature. A socket is better for testing. My socket was a proper HC49 socket temporarily "borrowed" out of a different unfinished project. But you can hunt around the junk box and another type of socket which will work Ok. The wires of the crystal are long enough that you can bend them slightly to fit in whatever socket you find to be suitable. Even with a socket, there was some initial drift due to the temperature stabilisation after me holding the crystal in my fingers.
?
73 Hans G0UPL
http://www.HansSummers.com

Re: CRYSTAL MEASUREMENTS

Hans Summers
 

开云体育

?
> Frequency reading is still moving / drifting,
> although circuit has been warming up about 5
> minutes.
> Q: How do you "note/catch" the frequency in this situation ?
?
Your circuit and method look Ok to me... how bad is the drift, and what happens if you wait longer than 5 minutes? The drift could also be in your frequency counter (or PC if you are using that as a frequency counter). The crystal itself will also drift, we tend to think of crystals as rock stable but they aren't at all. Relative to an LC oscillator maybe, but not in absolute terms. Just read about the problems I had getting a stable frequency in my 30m QRSS beacon (?and ).
?
In my BITX20 evaluation, I managed to find a socket which fit the crystals. If you are soldering the crystals in, you might find that the initial drift is rather high due to the crystal being so hot from the soldering iron and needing to cool back down to room temperature. A socket is better for testing. My socket was a proper HC49 socket temporarily "borrowed" out of a different unfinished project. But you can hunt around the junk box and another type of socket which will work Ok. The wires of the crystal are long enough that you can bend them slightly to fit in whatever socket you find to be suitable. Even with a socket, there was some initial drift due to the temperature stabilisation after me holding the crystal in my fingers.
?
73 Hans G0UPL
http://www.HansSummers.com
Re: BITX20 & BITX40

Bharat Balsavar
 

Hi Arv,

Thanks a lot for the very detailed reply to my query and for offering to advise me on any problems I might face with building the trx.

Knowing that I can bank on the group's knowledge and experience sure encourages me to experiment and learn and to build the project.

Very warm regards.
73s
-----
Bharat D Balsavar
VU2BDX





----Original Message Follows----
From: Arv Evans <arvevans@...>
Reply-To: BITX20@...
To: BITX20@...
Subject: Re: [BITX20] Re: BITX20 & BITX40
Date: Tue, 13 Jul 2004 12:22:44 -0600

Bharat

The discrete component AF Amplifier file is in the FILES and PHOTOS
sections of the BITX20 forum on Yahoo.com You should be able to view
and copy them from there. If you have problems please send me an email
<arvevans@...> and I will reply directly to your email with an
attached file of the audio amp that I used. Please be aware that I used
a 741 Op-Amp in place of the LM-386 in my BITX20, and built the discrete
component audio amplifier outboard in a speaker box. With just the
Op-Amp (configured for a gain of 100) there is plenty of audio to run
headphones (32 ohm Walkman style headphones with the earphone elements
in series). The discrete audio amp is necessary only if you want to
drive a speaker.
If you want to eliminate need for an Op-Amp, you could probably just use
a single transistor gain stage (much like Farhan's microphone amp
circuit) and a simple emitter follower for your receive audio. I will
try to work up a circuit diagram and test that sometime in the next few
days.

-----------------------------------------------------------------------------------------

CONSTRUCTION TIPS:

(1) Build both the RX audio section and the TX Microphone amplifier. By
powering up both simultaneously you can drive the RX amp with your TX
amp and microphone. This lets you test both audio sections before you
build the rest of the circuit.

(2) Build the IF Filter and the BFO. You can couple the output of your
BFO (use a 3 pf capacitor) to the filter input and tune the BFO to
determine your filter characteristics. You will need a method of
accurately measuring the BFO frequency, and a simple RF detector & high
impedance DC meter to measure filter output.

-----------------------------------------------------------------------------------------

For the front-end Band Pass Filter of the BITX40 I used a pair of 10.7
MHZ IF Transformers from an AM/FM transistor radio. These required 55
PF in parallel in order to bring them to resonance on 40 Meters. I used
the whole inductor and ignored the tap on these transformers. The
secondary winding of these was also ignored, but it might be interesting
to experiment with coupling the input and/or output via those windings.
A copy of the schematic and picture of this bandpass filter is in the
PHOTOS section of this forum. Look in the directory showing my call
sign (K7HKL).

NOTE: There was no particular reason for using the 10.7 IF transformers
other than that I had them available and wanted to experiment with using
them in a 40 Meter receiver. You can also use Farhan's design for the
front-end BPF (Band Pass Filter) and re-calculate & rewind the coils for
7.0 to 7.3 MHZ coverage.

IDEA: Maybe someone could experimentally determine the "inductance
versus turns" for tap washers and publish it on this forum. With that
info we could easily scale Farhan's design to almost any band.

My VFO is still not in a final stage of construction. I have built a
PTO (also shown in the PHOTOS section) but am still trying to obtain
exactly 10 KHZ per turn with good temperature stability. So far, that
has eluded me! I have spread and compressed the coils to adjust the
frequency coverage, but the turns on one end of the coil interact with
the other end of the coil. I seem to be getting close to my goal, but
it is still not at the point where I have an acceptably even spread of
frequency from one end of the band to the other.

Your BITX40 VFO will need to tune from 3.0 to 2.7 to cover 7.0 to 7.3
MHZ RX & TX if you use the standard 10 MHZ IF & BFO. Initial
calculations indicate that this places all first-order spurs and all 2nd
& 3rd harmonics outside the 40 Meter band. I admittedly have not done a
detailed analysis of complex mixing products to insure that there will
be absolutely no unwanted birdies within the passband.
NOTE: VU2ITI has published a good article (
Ceramic_Resonator_VFO_by_VU2ITI_SPARK.pdf ) on using a ceramic resonator
for VFO/VXO applications. If you can find a copy of that document you
might be able to apply something like this for your BITX40, assuming you
can find a ceramic resonator that is in the 3.0-2.7 MHZ range.

At this point I also have not completed an acceptable linear amplifier
section for 40 Meters. Plans are for this to probably be a push-pull
set of IRF-510 devices, but work on another transceiver (not the BITX40)
has taken priority over that effort. Obviously you can alter the
inductors of Farhan's design to make it work on 40 Meters, but I want to
go for a bit more power on 40, thus I will need to work up a different
design for the linear.

For my BITX40 I have built two different IF Filter modules. At this
point I am not sure which to use. The ladder filter using 10 MHZ
crystals did not tune up well for me (the one for my BITX20 worked
perfectly), probably because I used a set of older & larger 10 MHZ
crystals with apparently much different characteristics. I also built a
lattice filter for 10 MHZ. This seems to have less loss and a steeper
slope for exclusion of the upper sideband energy. However, I am still
tinkering with both filters and am not ready to publish anything about
them yet. If you are contemplating near-future completion of your
BITX40 you should probably closely follow Farhan's design for the IF
Filter and use the same brand (KDS) crystals that he recommends.

In the FILES section of the forum you will find a spreadsheet program
that calculates the VFO frequencies for BITX designs. This will also
let you explore a design that uses crystals other than 10 MHZ for the
filter and BFO. This might be handy if you are contemplating use of
something like TV color-burst crystals (3.579 MHZ) for your filter and
BFO (this is not recommended for a BITX40 though because your 3.579 MHZ
BFO second harmonic would be at 7.158 in the 40 Meter band). My
longer-term plan is to use color-burst crystals for an LF (0.160 to
0.190 MHZ) version of the BITX, but that will have to wait until I
finish the BITX40.

I will continue to publish portions of my BITX40 here on this forum as
each section is finished and tested. If you have any particular
problems please feel free to email me (I may be having the same
problem...) and maybe we can possibly resolve them together. The other
members of this forum are also a good source of ideas and solutions.

73's
Arv - K7HKL
_._

On Mon, 2004-07-12 at 23:46, Bharat D Balsavar wrote:

Hi Arv,

I'm thinking of building a 40m version of the BITX20. As Ashhar
mentions in one of his earlier mails, that is the band more popular
here in India.

Could you please guide me on the different stages of the circuit you
modified and the nature of changes you made?

Also, may I please have a copy of the gif file of the discreet
components AF Amplifier?

Thanks in advance.
73s,
Bharat, VU2BDX


--- In BITX20@..., arvevans@e... wrote:
Hello to the BITX20 group (this is my first posting on this forum).

Farhan and myself have exchanged a couple of off-forum emails
regarding mods to his excellent design. One interesting possibility
is replacement of the LM-386 with a discrete component AF Amplifier.
He said that he had not had the time to work up a schematic...so I
have provided one (see attached .gif file). This can allow those
without access to an LM-386 to build the unit.

Also, my layout for the BITX20 uses 10.7 MHZ IF transformers
salvaged from dead AM/FM radios ( I dislike winding toroids! ). My
construction is a BITX40 (40 Meters) and requires 55 pf across the
10.7 IFs to resonate on 7.2 MHZ. These 10.7 IF transformers might be
made to resonate on 20M if the internal capacitors were removed (
break them with a screwdriver point ) and a small variable ( 5-25pf )
used to bring them to resonance.

73's
Arv - K7HKL

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Re: Inexpensive plastic screwdriver

Arv Evans
 

开云体育

Paolo

In the US, plastic knitting needles are available for an attractive price.? These range from 1/8 inch to 1/2 inch diameter.? The smaller ones are easily ground to a screwdriver point using sandpaper taped to a flat surface.
If one is careful you can even shape them to hex or octagon shapes for adjusting slug tuned coils.

TIP:
For trial testing of coils to see if they need increased or decreased inductance you can build a simple tool to temporarily shift the inductance up or down.? Use a plastic drinking straw and insert a small brass rod (about 1/4 inch long) into one end.? Insert a small rod of ferrite material (a chunk of broken ferrite ring works fine) in the other end.? Now you can temporarily insert either end into your coil-under-test and observe the results.? The brass will cause an increase in frequency (decreased inductance) and the ferrite will cause a decrease in frequency (increased inductance).
No, I have not tried this with the "Tap Washer Toroids" used in the BITX20, but I will later today because I am curious to see what the results might be.

Arv
_._
On Tue, 2004-07-13 at 01:52, Paolo Cravero as2594 wrote:

Hi,
following Arv Evans's useful tips I would like to share with you how I
built a non-conductive screwdriver to regulate capacitor trimmers.

A quick glance at the BITX20 schematic did not reveal any "floating"
trimcap, all of them have at least one terminal to ground.
In these situations it is important to know that the trimmer screw is
electrically connected to one of the trimcap terminals: solder that
terminal to ground! This way you can use any screwdriver without
detuning the circuit with your hand.
Use an ohm-meter between the screw and terminals to identify which
one(s) are to be grounded.
(This might be obvious, but I didn't know until a few monhts ago!)

If the trimcap is floating instead, you need a plastic screwdriver.
Since it might be rather expensive to buy (at least in Italy) I built
one out of a toothbrush. Toothbrush should be changed often, ;-), and it
is usually made of some hard plastic (+ rubber for a better grip).

So, cut off the brush and shape the stick with a knife until you come up
with something that looks like a screwdriver (flat) head. I found the
plastic to be quite resistant, so you need to work it in small steps as
if you were creating a wood sculpture.

Apply the usual disclaimer about personal safety while handling the
knife and you're on the way to have a simple and ergonomical all-plastic
screwdriver.

Has anyone identified other materials that could be used for such a purpose?

72,
Paolo IK1ZYW

--
QRPp-I #707? + www.paolocravero.tk +? I QRP #476
?? Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

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Re: BITX20 & BITX40

Arv Evans
 

开云体育

Bharat

The discrete component AF Amplifier file is in the FILES and PHOTOS sections of the BITX20 forum on Yahoo.com? You should be able to view and copy them from there.? If you have problems please send me an email and I will reply directly to your email with an attached file of the audio amp that I used.? Please be aware that I used a 741 Op-Amp in place of the LM-386 in my BITX20, and built the discrete component audio amplifier outboard in a speaker box.? With just the Op-Amp (configured for a gain of 100) there is plenty of audio to run headphones (32 ohm Walkman style headphones with the earphone elements in series).? The discrete audio amp is necessary only if you want to drive a speaker.?
If you want to eliminate need for an Op-Amp, you could probably just use a single transistor gain stage (much like Farhan's microphone amp circuit) and a simple emitter follower for your receive audio.? I will try to work up a circuit diagram and test that sometime in the next few days.

-----------------------------------------------------------------------------------------

CONSTRUCTION TIPS:

(1) Build both the RX audio section and the TX Microphone amplifier.? By powering up both simultaneously you can drive the RX amp with your TX amp and microphone.? This lets you test both audio sections before you build the rest of the circuit.

(2) Build the IF Filter and the BFO.? You can couple the output of your BFO (use a 3 pf capacitor) to the filter input and tune the BFO to determine your filter characteristics.? You will need a method of accurately measuring the BFO frequency, and a simple RF detector & high impedance DC meter to measure filter output.

-----------------------------------------------------------------------------------------

For the front-end Band Pass Filter of the BITX40 I used a pair of 10.7 MHZ IF Transformers from an AM/FM transistor radio.? These required 55 PF in parallel in order to bring them to resonance on 40 Meters.? I used the whole inductor and ignored the tap on these transformers.? The secondary winding of these was also ignored, but it might be interesting to experiment with coupling the input and/or output via those windings.? A copy of the schematic and picture of this bandpass filter is in the PHOTOS section of this forum.? Look in the directory showing my call sign (K7HKL).

NOTE: There was no particular reason for using the 10.7 IF transformers other than that I had them available and wanted to experiment with using them in a 40 Meter receiver.? You can also use Farhan's design for the front-end BPF (Band Pass Filter) and re-calculate & rewind the coils for 7.0 to 7.3 MHZ coverage.?

IDEA:? Maybe someone could experimentally determine the "inductance versus turns" for tap washers and publish it on this forum.? With that info we could easily scale Farhan's design to almost any band.

My VFO is still not in a final stage of construction.? I have built a PTO (also shown in the PHOTOS section) but am still trying to obtain exactly 10 KHZ per turn with good temperature stability.? So far, that has eluded me!? I have spread and compressed the coils to adjust the frequency coverage, but the turns on one end of the coil interact with the other end of the coil.? I seem to be getting close to my goal, but it is still not at the point where I have an acceptably even spread of frequency from one end of the band to the other.?

Your BITX40 VFO will need to tune from 3.0 to 2.7 to cover 7.0 to 7.3 MHZ RX & TX if you use the standard 10 MHZ IF & BFO.? Initial calculations indicate that this places all first-order spurs and all 2nd & 3rd harmonics outside the 40 Meter band.? I admittedly have not done a detailed analysis of complex mixing products to insure that there will be absolutely no unwanted birdies within the passband.
NOTE: VU2ITI has published a good article ( Ceramic_Resonator_VFO_by_VU2ITI_SPARK.pdf ) on using a ceramic resonator for VFO/VXO applications.? If you can find a copy of that document you might be able to apply something like this for your BITX40, assuming you can find a ceramic resonator that is in the 3.0-2.7 MHZ range.

At this point I also have not completed an acceptable linear amplifier section for 40 Meters.? Plans are for this to probably be a push-pull set of IRF-510 devices, but work on another transceiver (not the BITX40) has taken priority over that effort.? Obviously you can alter the inductors of Farhan's design to make it work on 40 Meters, but I want to go for a bit more power on 40, thus I will need to work up a different design for the linear.

For my BITX40 I have built two different IF Filter modules.? At this point I am not sure which to use.? The ladder filter using 10 MHZ crystals did not tune up well for me (the one for my BITX20 worked perfectly), probably because I used a set of older & larger 10 MHZ crystals with apparently much different characteristics.? I also built a lattice filter for 10 MHZ.? This seems to have less loss and a steeper slope for exclusion of the upper sideband energy.? However, I am still tinkering with both filters and am not ready to publish anything about them yet.? If you are contemplating near-future completion of your BITX40 you should probably closely follow Farhan's design for the IF Filter and use the same brand (KDS) crystals that he recommends.

In the FILES section of the forum you will find a spreadsheet program that calculates the VFO frequencies for BITX designs.? This will also let you explore a design that uses crystals other than 10 MHZ for the filter and BFO.? This might be handy if you are contemplating use of something like TV color-burst crystals (3.579 MHZ) for your filter and BFO (this is not recommended for a BITX40 though because your 3.579 MHZ BFO second harmonic would be at 7.158 in the 40 Meter band).? My longer-term plan is to use color-burst crystals for an LF (0.160 to 0.190 MHZ) version of the BITX, but that will have to wait until I finish the BITX40.

I will continue to publish portions of my BITX40 here on this forum as each section is finished and? tested.? If you have any particular problems please feel free to email me (I may be having the same problem...) and maybe we can possibly resolve them together.? The other members of this forum are also a good source of ideas and solutions.

73's
Arv - K7HKL
_._

On Mon, 2004-07-12 at 23:46, Bharat D Balsavar wrote:

Hi Arv,

I'm thinking of building a 40m version of the BITX20. As Ashhar
mentions in one of his earlier mails, that is the band more popular
here in India.

Could you please guide me on the different stages of the circuit you
modified and the nature of changes you made?

Also, may I please have a copy of the gif file of the discreet
components AF Amplifier?

Thanks in advance.
73s,
Bharat, VU2BDX


--- In BITX20@..., arvevans@e... wrote:
> Hello to the BITX20 group (this is my first posting on this forum).
>
> Farhan and myself have exchanged a couple of off-forum emails
regarding mods to his excellent design.? One interesting possibility
is replacement of the LM-386 with a discrete component AF Amplifier.?
He said that he had not had the time to work up a schematic...so I
have provided one (see attached .gif file).? This can allow those
without access to an LM-386 to build the unit.
>
> Also, my layout for the BITX20 uses 10.7 MHZ IF transformers
salvaged from dead AM/FM radios ( I dislike winding toroids! ).? My
construction is a BITX40 (40 Meters) and requires 55 pf across the
10.7 IFs to resonate on 7.2 MHZ.? These 10.7 IF transformers might be
made to resonate on 20M if the internal capacitors were removed (
break them with a screwdriver point ) and a small variable ( 5-25pf )
used to bring them to resonance.
>
> 73's
> Arv - K7HKL


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Binocular Cores

Mike W
 

I have found a 'source' of minature binocular balun cores in old UHF
TV tuners and computer UHF modulators. there are usually, it
appears, one or two per tuner. Not tried them yet though.
atb Mike W, G8NXD
CRYSTAL MEASUREMENTS

MILAREPA
 

开云体育

Dear forum,
I try to measure my 12 MHz IF-crystals with method here,
for purpose selection within 30 to 50 KHz ( is this value right ? ).
But the problem is:
Frequency reading is still moving / drifting,
although circuit has been warming up about 5 minutes.
Q: How do you "note/catch" the frequency in this situation ?
( like Hans Summer's ...:? Here are my measurements in ascending order:
9,994,677
9,994,704
9,994,733
9,994,747
9,994,799??? 0
9,994,811??? +12
9,994,821??? +22
9,994,829??? +30
9,994,874
9,994,887
You can see the chosen 4, which are within 30 Hz.
I wouldn't have been able to match a second set within 45Hz... )
===
My measurement method:
I have?modified BITX-VFO with 3 transistors Q5, Q6 and Q7.
But?I remove the coil L4?and T1 etc.,
replace it with crystal for the purpose of measurement as :
NB:
- I use 12.00 MHz?crystals for my BITX.
- My counter is homemade, One 7 segment counter by PA2OHH
since the 7 segment diplay is 100 Hz accuracy (ex. : 12 000.0 KHz),
I use RS232 for display frequency at computer for more accuracy
as ex. : 12. 123 456 MHz ).
Re: Inexpensive plastic screwdriver

Hubert Smits
 

Hi Paolo,

I cut/filed a piece of PCB to the right size and
sanded of the copper. The slight advantage over a
toothbrush is that the material is less soft, so it
can handle screws that are tight or stuck.

72 de Hubert

--- Paolo Cravero as2594 <pcravero@...> wrote:

Hi,
following Arv Evans's useful tips I would like to
share with you how I
built a non-conductive screwdriver to regulate
capacitor trimmers.
Re: Inexpensive plastic screwdriver

Paolo Cravero as2594
 

Mike W wrote:

following Arv Evans's useful tips I would like to share with you how I
built a non-conductive screwdriver to regulate capacitor trimmers.
Whats wrong with the old plastic knitting needle ?. When playing with HV circuits they are a lot longer and therefore safer.
WOW! Got to ask my mother if she has some spare plastic ones!

For those non-native English speakers that might wonder what a "knitting needle" is, see the description here or just the picture here

Now I wonder if knitting needles are more widespread than toothbrushes! :-)

Paolo

PS: if someone ever makes a component bag for BITX20 s/he should consider adding a knitting needle or a toothbrush to the complete set of tap washers! :-)

--
QRPp-I #707 + www.paolocravero.tk + I QRP #476
Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC
Re: Inexpensive plastic screwdriver

Mike W
 

On 13 Jul 04, at 9:52, Paolo Cravero as2594 wrote:

Hi,
following Arv Evans's useful tips I would like to share with you how I
built a non-conductive screwdriver to regulate capacitor trimmers.
Whats wrong with the old plastic knitting needle ?. When playing
with HV circuits they are a lot longer and therefore safer.

Another useful tool is a tuning wand, brass ferrule on one end of a
knitting needle and a ferrite ferrule on 'tother. When placed into the
flux field of a coil the ferrite end raises the inductance and the
brass end reduces it. Enabling a relativly easy way to determine if
the coil is too big or too small. Sadly, AFIK, it does'nt work with
toroids though.
atb Mike W
--
Relay question Help!

Rahul Srivastava
 

Hi!

I recall reading about the two relay placement being helpful in avoiding RF pickup.

I would be obliged if?the someone will give me the new configration.

73

Rahul VU3WJM?

Do you Yahoo!?
- Send 10MB messages!
Re: Inexpensive plastic screwdriver

Rahul Srivastava
 

Hi!
?
I?fashion them out of?glass epoxy PCB material. Much scrapped double sided? PC boards are available..?cut a strip from?area without copper traces ie normally the edges .
File and shape the strip to the desired size of screwdriver you want.
Good durable?non-conductive tool it is.
?
73
?
Rahul VU3WJM
?
?
?
?

Paolo Cravero as2594 wrote:
Hi,
following Arv Evans's useful tips I would like to share with you how I
built a non-conductive screwdriver to regulate capacitor trimmers.

A quick glance at the BITX20 schematic did not reveal any "floating"
trimcap, all of them have at least one terminal to ground.
In these situations it is important to know that the trimmer screw is
electrically connected to one of the trimcap terminals: solder that
terminal to ground! This way you can use any screwdriver without
detuning the circuit with your hand.
Use an ohm-meter between the screw and terminals to identify which
one(s) are to be grounded.
(This might be obvious, but I didn't know until a few monhts ago!)

If the trimcap is floating instead, you need a plastic screwdriver.
Since it might be rather expensive to buy (at least in Italy) I built
one out of a toothbrush. Toothbrush should be changed often, ;-), and it
is usually made of some hard plastic (+ rubber for a better grip).

So, cut off the brush and shape the stick with a knife until you come up
with something that looks like a screwdriver (flat) head. I found the
plastic to be quite resistant, so you need to work it in small steps as
if you were creating a wood sculpture.

Apply the usual disclaimer about personal safety while handling the
knife and you're on the way to have a simple and ergonomical all-plastic
screwdriver.

Has anyone identified other materials that could be used for such a purpose?

72,
Paolo IK1ZYW

--
QRPp-I #707? + www.paolocravero.tk +? I QRP #476
?? Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC

Do you Yahoo!?
- 100MB free storage!
Inexpensive plastic screwdriver

Paolo Cravero as2594
 

Hi,
following Arv Evans's useful tips I would like to share with you how I built a non-conductive screwdriver to regulate capacitor trimmers.

A quick glance at the BITX20 schematic did not reveal any "floating" trimcap, all of them have at least one terminal to ground.
In these situations it is important to know that the trimmer screw is electrically connected to one of the trimcap terminals: solder that terminal to ground! This way you can use any screwdriver without detuning the circuit with your hand.
Use an ohm-meter between the screw and terminals to identify which one(s) are to be grounded.
(This might be obvious, but I didn't know until a few monhts ago!)

If the trimcap is floating instead, you need a plastic screwdriver. Since it might be rather expensive to buy (at least in Italy) I built one out of a toothbrush. Toothbrush should be changed often, ;-), and it is usually made of some hard plastic (+ rubber for a better grip).

So, cut off the brush and shape the stick with a knife until you come up with something that looks like a screwdriver (flat) head. I found the plastic to be quite resistant, so you need to work it in small steps as if you were creating a wood sculpture.

Apply the usual disclaimer about personal safety while handling the knife and you're on the way to have a simple and ergonomical all-plastic screwdriver.

Has anyone identified other materials that could be used for such a purpose?

72,
Paolo IK1ZYW

--
QRPp-I #707 + www.paolocravero.tk + I QRP #476
Beacon @ 28.3219 MHz + QRPp + QRSS3 + JN35TC
Re: BITX20 & BITX40

Bharat D Balsavar
 

Hi Arv,

I'm thinking of building a 40m version of the BITX20. As Ashhar
mentions in one of his earlier mails, that is the band more popular
here in India.

Could you please guide me on the different stages of the circuit you
modified and the nature of changes you made?

Also, may I please have a copy of the gif file of the discreet
components AF Amplifier?

Thanks in advance.
73s,
Bharat, VU2BDX


--- In BITX20@..., arvevans@e... wrote:
Hello to the BITX20 group (this is my first posting on this forum).

Farhan and myself have exchanged a couple of off-forum emails
regarding mods to his excellent design. One interesting possibility
is replacement of the LM-386 with a discrete component AF Amplifier.
He said that he had not had the time to work up a schematic...so I
have provided one (see attached .gif file). This can allow those
without access to an LM-386 to build the unit.

Also, my layout for the BITX20 uses 10.7 MHZ IF transformers
salvaged from dead AM/FM radios ( I dislike winding toroids! ). My
construction is a BITX40 (40 Meters) and requires 55 pf across the
10.7 IFs to resonate on 7.2 MHZ. These 10.7 IF transformers might be
made to resonate on 20M if the internal capacitors were removed (
break them with a screwdriver point ) and a small variable ( 5-25pf )
used to bring them to resonance.

73's
Arv - K7HKL
Re: Cleaning PC Board material for your BITX transceiver construction

Jim Strohm
 

On Jul 11, 2004, at 8:53 PM, bainopaul wrote:

Brasso is another cleaner that I have used in the past. Does an
excellent job!
I'd like to remind all that ScotchBrite is a relatively non-reactive abrasive matrix that works well with reasonably non-reactive chemicals. It's worth trying with Tarn-X or other "tarnish-removing" chems. I'm going to experiment with a few other commonly (globally) available chems.


I'll report what I find, unless I find something that combusts.

Jim N6OTQ
Re: Cleaning PC Board material for your BITX transceiver construction

 

Brasso is another cleaner that I have used in the past. Does an
excellent job!




73 de Baino


--- In BITX20@..., "Bruce Raymond" <bruceraymond@s...>
wrote:
I'd like to suggest the use of a copper/silver cleaner, such as
Tarn-X. I don't know
what would be similar across the pond or in other parts of the
world. I just pour a
little bit of Tarn-X on a paper towel or rag and then wipe the
pcb. Be sure to wash
off the Tarn-X residue with water when you're done. I've heard of
people using
toilet bowl cleaners and such, but this appears to be more
benign. It does a
reasonable job, although not as good as a serious session with
steel wool. OTOH,
it's a *lot* less work ;-)

- Bruce ND8I


-----Original Message-----
From: Charles Darley [mailto:charles@d...]
Sent: Friday, July 09, 2004 2:55 PM
To: BITX20@...
Subject: RE: [BITX20] Cleaning PC Board material for your BITX
transceiver construction


Hi
Can I also suggest that where the components are to be placed
that the PCB pad is tinned and where earth connections are to be
made that area too is tinned, as it ensures a good joint and the
joint is quicker too!!



I think the sort of bush mentioned has brass wire bristles and
used for cleaning suede shoes !!


Charles G4VSZ


-----Original Message-----
From: Arv Evans [mailto:arvevans@e...]
Sent: 09 July 2004 19:00
To: bitx20@...; rlelm@a...; leatkin@e...;
bequan@m...; ciresnave@y...
Subject: [BITX20] Cleaning PC Board material for your BITX
transceiver construction


Hi

PC Board material that is stored for some time usually takes on
a layer of oxidation that hinders soldering components to its
surface. In the past I have routinely used sandpaper to remove this
oxidation and prepare the surface for my "ugly construction"
projects. Now I think I might have found a better way to prepare
the surface. I tried a small wire brush and found that it not only
removes surface oxidation, it also leaves a much more polished
surface and requires less effort. The wire brush was purchased at a
local hobby store for about $1 US, see the picture below. If you
have a small wire brush you might try it and see if it works for you.



73's
Arv
_._



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Re: Cleaning PC Board material for your BITX transceiver construction

Mr. D.Walters
 

?
Would those be "Blue -?blue, blue suede shoes?"
?
Theo
?

----- Original Message -----
Sent: Friday, July 09, 2004 7:55 PM
Subject: RE: [BITX20] Cleaning PC Board material for your BITX transceiver construction

Hi

Can I also suggest that where the components are to be placed that the PCB pad is tinned?and where earth connections are to be made that area too is tinned, as it ensures a good joint and?the joint is quicker too!!?

?

I think the sort of bush mentioned has brass wire bristles and used for cleaning suede shoes !!

?
Charles? G4VSZ
?
?
?-----Original Message-----
From: Arv Evans [mailto:arvevans@...]
Sent: 09 July 2004 19:00
To: bitx20@...; rlelm@...; leatkin@...; bequan@...; ciresnave@...
Subject: [BITX20] Cleaning PC Board material for your BITX transceiver construction

Hi

PC Board material that is stored for some time usually takes on a layer of oxidation that hinders soldering components to its surface.? In the past I have routinely used sandpaper to remove this oxidation and prepare the surface for my "ugly construction" projects.? Now I think I might have found a better way to prepare the surface.? I tried a small wire brush and found that it not only removes surface oxidation, it also leaves a much more polished surface and requires less effort.? The wire brush was purchased at a local hobby store for about $1 US, see the picture below.? If you have a small wire brush you might try it and see if it works for you.



73's
Arv
_._
Re: [AQRP] FW: Inexpensive capacitor measurements...

John Fisher
 

Thanks a million, Monty, Great job. And thanks to Arv Evans for sharing
this circuit :-)


Regards,
John

=============================================
email: k5jhf@...
photos:
files:
webpage:
callsign: K5JHF
=============================================

-----Original Message-----
From: Monty N5ESE [mailto:n5ese@...]
Sent: Friday, July 09, 2004 12:56 PM
To: John Fisher
Cc: AQRP
Subject: Re: [AQRP] FW: [BITX20] Inexpensive capacitor measurements...


Gang:

Here's an ASCII schematic to replace the missing GIF image in the
posting below. If it doesn't look right in your mail client, cut and
paste it into Notepad or your favorite word processor, and set the font
to courier or courier new.

I highly recommend that you install the 1000 pF calibration capacitor in
the circuit with a switch to switch it in and out as required, in case
your original "calibration" drifts. There are lots of things that can
affect measurement accuracy and stability in this circuit: line
frequency; line voltage changes; R1's potentiometer stability,
resolution and settability; your meter's linearity, and your meter's AC
input impedance.

A wall-wart (AC, not DC) would be an ideal transformer, comes pre-fused,
and keep you away from line voltages. A nominal 9 or 12 VAC wall-wart
would probably end up providing 15 VAC in this application.

Your $9 Harbor Freight Digital Voltmeter probably won't be very accurate
at low readings (say, below 100-150 pF), but try it and see.

By the way, you don't have to have exactly 1000pF for your cal
capacitor.
If you have something close, and you know what it is by virtue of its
tolerance or because you can measure it with a lab instrument at work,
that's good enough. For example, if it's a 1000pF NPO ceramic and you
know that its actual value is 1090 pF, adjust the pot so the meter reads
1.09 VAC. As another example, suppose you have a 2% 910 pF silver mica
- just adjust the pot so that the meter reads 0.91 VAC.

I wouldn't trust measurement readings below 50 or so pF very much...
stray capacitances in the layout, meter probes, and meter input
circuitry will begin to contribute significant errors as the capacitance
approaches lower values.

Still, it's a great little circuit!

73,
monty N5ESE

-----------------------------
Capacitance Measuring Circuit
-----------------------------
(view with monospace font like Courier)

Cx
__o-F-o__
) ________o---||---o_____
)|( |
)|( __________|
)|( 15 | |
115VAC )|( VAC &#92;|/ |
)|( R1 | |
)|(________/&#92;/&#92;/&#92;/&#92;_______|
) ^ ^
_________) | 180K (typ) |
| |
| ____ |
| | | |
|___| AC |___|
| VM |
|____|


I really like this BITX20 list on Yahoo groups. They're building up a
cheap rig and sending out great information :-)


Regards,
John

=============================================
email: k5jhf@...
photos:
files:
webpage:
callsign: K5JHF
=============================================

-----Original Message-----
From: Arv Evans [mailto:arvevans@...]
Sent: Thursday, July 08, 2004 3:35 PM
To: bitx20@...
Subject: [BITX20] Inexpensive capacitor measurements...


Hi

Since Farhan's stated original intent in designing the BITX20 was to
provide an inexpensive transceiver, maybe it would be appropriate to
show BITX builders an inexpensive way to measure unmarked or
questionable capacitors. The following circuit came to me via Don
Metzger - K8JWR, but I suspect the method has been around for quite
some time. The picture shown here is the relatively simple schematic
for this tool.



Use a mains transformer that delivers a few ma. at about 15 volts RMS.
Connect a known .001 mfd capacitor at Cx and adjust the value of R1 (
for R1 I used a 250K trim pot salvaged from an old circuit card ) for
an indication of 1.000 volts on your DVM. Now you can measure
capacitor values from a few pf up to 0.001 mfd by connecting them in
the place of Cx.

I used this method to "calibrate" the knob indicator on a 3X450 pf
variable capacitor that I regularly use as part of my test equipment
repertoire. Now I just set the dip meter to the desired frequency,
and use the variable capacitor to tune my inductor for a dip on that
setting. Once the coil is on-frequency I can read the capacitance
from my calibrated variable capacitor and substitute that value of
fixed capacitance into the circuit.

Part of the fun derived from building your own ham radio equipment is
in devising ways to perform complex design and testing by use of
relatively simple and inexpensive methods & equipment. This idea fits
into that category.

73's
Arv
_._

Before someone asks the question...No, this circuit will not measure
electrolytic capacitors, but it will get you close enough for most of
the small caps you will be using in designing resonant circuits for HF
applications.
---------------------------------------------------------







Via the Austin QRP Club list
Yahoo! Groups Links







Via the Austin QRP Club list
Yahoo! Groups Links
Re: Cleaning PC Board material for your BITX transceiver construction

Bruce Raymond
 

?
I'd like to suggest the use of a copper/silver cleaner, such as Tarn-X.? I don't know
what would be similar across the pond or in other parts of the world.? I just pour a
little bit of Tarn-X on a paper towel or rag and then wipe the pcb.? Be sure to wash
off the Tarn-X residue with water when you're done.? I've heard of people using
toilet bowl cleaners and such, but this appears to be more benign.? It does a
reasonable job, although not as good as a serious session with steel wool.? OTOH,
it's a *lot* less work? ;-)
?
- Bruce? ND8I
?
?

-----Original Message-----
From: Charles Darley [mailto:charles@...]
Sent: Friday, July 09, 2004 2:55 PM
To: BITX20@...
Subject: RE: [BITX20] Cleaning PC Board material for your BITX transceiver construction

Hi

Can I also suggest that where the components are to be placed that the PCB pad is tinned?and where earth connections are to be made that area too is tinned, as it ensures a good joint and?the joint is quicker too!!?

?

I think the sort of bush mentioned has brass wire bristles and used for cleaning suede shoes !!

?
Charles? G4VSZ
?
?
?-----Original Message-----
From: Arv Evans [mailto:arvevans@...]
Sent: 09 July 2004 19:00
To: bitx20@...; rlelm@...; leatkin@...; bequan@...; ciresnave@...
Subject: [BITX20] Cleaning PC Board material for your BITX transceiver construction

Hi

PC Board material that is stored for some time usually takes on a layer of oxidation that hinders soldering components to its surface.? In the past I have routinely used sandpaper to remove this oxidation and prepare the surface for my "ugly construction" projects.? Now I think I might have found a better way to prepare the surface.? I tried a small wire brush and found that it not only removes surface oxidation, it also leaves a much more polished surface and requires less effort.? The wire brush was purchased at a local hobby store for about $1 US, see the picture below.? If you have a small wire brush you might try it and see if it works for you.



73's
Arv
_._
Re: Cleaning PC Board material for your BITX transceiver construction

 

?
Hi

Can I also suggest that where the components are to be placed that the PCB pad is tinned?and where earth connections are to be made that area too is tinned, as it ensures a good joint and?the joint is quicker too!!?

?

I think the sort of bush mentioned has brass wire bristles and used for cleaning suede shoes !!

?
Charles? G4VSZ
?
?
?-----Original Message-----
From: Arv Evans [mailto:arvevans@...]
Sent: 09 July 2004 19:00
To: bitx20@...; rlelm@...; leatkin@...; bequan@...; ciresnave@...
Subject: [BITX20] Cleaning PC Board material for your BITX transceiver construction

Hi

PC Board material that is stored for some time usually takes on a layer of oxidation that hinders soldering components to its surface.? In the past I have routinely used sandpaper to remove this oxidation and prepare the surface for my "ugly construction" projects.? Now I think I might have found a better way to prepare the surface.? I tried a small wire brush and found that it not only removes surface oxidation, it also leaves a much more polished surface and requires less effort.? The wire brush was purchased at a local hobby store for about $1 US, see the picture below.? If you have a small wire brush you might try it and see if it works for you.



73's
Arv
_._
115361 - 115380 of 115556