Hi,
at this moment I spend hours getting the filter working for the IF
frequency of 4.9152 MHz.
It is importand that measurements are done with the circuits
connected, it seems that the load determines the passband a lot.
To have an idea about the functioning of the filter, I connected my
LF generator to the microphone connection. Measuring the output of
Q12 (with an osciloscoop or a mw meter), you see variation of the
output level while variating the LF frequency.
For the filter I made, it learned me that my filter had some peaks
that were not close together. Playing with different capacitor
values took a lot of time but with capacitor values of 68pF, 82pF,
68pF I have peaks at 1052Hz, 1538Hz, 2000Hz (after I also corrected
the coil in the BFO to get the peaks on the right places). With a
mircophone connected, I see output while talking in the microphone.
Between the peaks, the output is not completely down but I think the
filter shape is not flat enough. This weekend, I will play with some
additional serie coils, may be the impedance of the filter is much
higher then the circuit. (I hope the peaks do not shift again ;-( ).
Anyone else suggestions?

By the way, for the ones that want to see it with an analyser: may
be the BFO signal can be connected to both mixers resulting in audio
frequency mix up, filtered and down to LF again. Then a spectrum
analyser can be used with the PC sound card? (pink noise to the
microphone terminal, output of the mixer to the LF sound card input).
Just a thought, not tried.

Lets experiment further!
Chris, PA3CRX

Please I do not have the 10MHz crystals to make the filter, but

I

have 5 pieces of 8MHz crystals with this 8MHz crystals is

possible to

make the filter with new values of resistor and capacitor?>

3) To test my crystal filter I built the BFO circuit from the

BITX20 design on a separate of circuit board and added the inductor
and variable capacitor in series with the crystal. This gave me a
very stable oscillator that could be tuned across the filter

passband

to determine the shape factor. This signal was injected into the
input of the filter and a simple diode & capacitor type RF detector
was used with my voltmeter to measure the output. I do have a
frequency counter so I was able to determine the exact frequency

that

was being output by my test oscillator. As the frequency was

varied I

was able to plot the output voltage on a sheet of grid paper. I

would

assume that you might do something similar in building your filter
using 8 MHz crystals.

Hi all

Looking at the PA diagram it is indicated that from the antenna there
are two inductors L1 and L2 but the details below indicate L4 and L5.

Can anyone confirm that L1 = L4 and L2 = L5

73 G4VSZ Charles

开云体育

In the "files" section of this forum I have uploaded a small
spreadsheet program called "RESONANCE CALCULATOR.xls". This is a
spreadsheet program that helps calculate inductance, capacitance, or
frequency for various combinations of L and C. I found this very
handy in re-calculating the inductance values for converting Farhan's
BITX20 design into a BITX40 transceiver.

This is a Microsoft (tm) Excel spreadsheet, but if you do not have
MS-Excel all is not lost. You can go to <www.OpenOffice.org> and
download their FREE Open Office program. The spredsheet tool in Open
Office can read and execute MS-Excel programs. FYI: Open Office is
available for both MS-Windows and Linux, so if you are a Linux user
like me you now can have an equivalent of all the MS-Office tools for
FREE!

If anyone has problems with this spreadsheet, please let me know
because I can easily generate and upload both MS and OpenOffice
specific versions of this tool. If you need to "unlock" the
spreadsheet to make your own changes to the layout or formula, also
please let me know and I can provide you with the program password.

Arv - K7HKL

I found it (surprised myself). It's now in the file section in a folder named "hp_parts_xref".
Six .gifs, all about 250K.

I found these files on the internet a few years ago and as far as I know it's fair game for
sharing with others.

It would be nice if some day this got converted to text, but since I won't start today, I
won't ask anybody else to, either!! We have things to build. I'm salvaging some PC boards
today with my hot-air gun. I think I've made about USD$3 already -- in just half an hour.

Jim N6OTQ

On Jul 2, 2004, at 10:37 AM, Arvid Evans wrote:

I first buiilt the BITX20 and am now working on a BITX40 version.
That way I can compare DC voltages and RF & AF signals with a working
unit as I complete the 40 Meter version.

Here are some changes that are being incorporated into my BITX40 as I
modify Farhan's design for 40 Meters, and to fit the contents of my
junk box

Builders are reminded that while the IRF510 final may be a little hard to find and may be a little expensive, many other power FETs will amplify quite nicely on lower frequencies, .

In the late 1980s and early 1990s, some ARRL members performed experiments with power FETs salvaged from switching power supplies. Their results as published in QST indicated that almost everything worked well at 40 meters or below.

Builders are especially reminded that IBM vastly over-engineered and de-rated power supplies for its minicomputers such as the AS/400, and a lot of those are coming onto the surplus market -- or winding up in landfills. These are EXCELLENT sources for builder parts -- with the caveat that lmost every semiconductor is marked with an IBM part number, so you'll need to bin parts as you remove them. The DIP ICs are all useless, except for use as art supplies.

I don't have a lot of experience with Hewlett-Packard minis, but most of the old 3000s, 5000s, and some 9000s should be surfacing soon, for the last gasp before the dust-bin. I **do** have a partial cross-reference for HP-numbered semiconductors, so these ARE worth hanging onto.

I'll post the list to the files section here when I find it. Alas, it's a .gif and I don't feel like typing it into a text file, and the reproduction quality is bad enough that OCR won't read it reliably.

Jim N6OTQ

All components arrived here today. I have counted them all out into the
component packs and despatched them.

Note that I have two spare packs, if any latecomers would like one: price is
?8 + ?0.28 UK postage, or whatever 50g costs to your country. These
components are at supplied by me at cost, from Farnell, Rapid Electronics
and Mode Components. Many are discounted due to bulk buy crystals,
transistors etc in QTY 100+. The pack comprises all semiconductors, crystals
and variable capacitors: 10x 10MHz xtals, 25x BC547B, 2N2218, IRF510, 15x
1N4148, 36V Zener, 9V1 Zener, 5V6 Zener, LM386N-1, 5x 22pF trimmer,
miniature 200pF tuning capacitor.

72/3 de Hans G0UPL

--- In BITX20@..., "felipetanaweb" <felipetanaweb@b...> wrote:

Please I do not have the 10MHz crystals to make the filter, but I
have 5 pieces of 8MHz crystals with this 8MHz crystals is possible to
make the filter with new values of resistor and capacitor?And to
modify the Bitx20 to Bitx40 is only to modify the Band Pass filter
and de oscillator?Somebody has this modification?

Thanks!

Felipe

I first buiilt the BITX20 and am now working on a BITX40 version.
That way I can compare DC voltages and RF & AF signals with a working
unit as I complete the 40 Meter version.

Here are some changes that are being incorporated into my BITX40 as I
modify Farhan's design for 40 Meters, and to fit the contents of my
junk box:

1) I used 10.7 MHz IF transformers from an old AM/FM radio to
build the front-end bandpass circuit. There is a photograph and
schematic of this in the "photos" section of this web forum under my
callsign, K7HKL.
2) Since I am using the original 10 MHz crystal filter design, my
VFO needs to tune 7.0 to 7.3 MHz below the IF frequency. That means
that the VFO range will be from 3.0 to 2.7 MHz. Since that is a bit
lower in frequency than in Farhan's BITX20, the oscillator coil will
need more turns. In my BITX40 version I did not use the BITX20 VFO
design. Instead I am using a PTO (Pearmability Tuned Oscillator)
design that is close to what WA6OTP is selling in kit form ( see
<www.wa6otp.com&#92;pto.htm> for a picture of Jim's design ), but my PTO
is for 3.0 to 2.7 MHz. Using this PTO design for the VFO avoided the
need for the higher voltage (36 V) zener diode and also eliminated the
need for using two separate tuning capacitors (a larger band-set and
the smaller zener fine-tuning capacitor). My VFO capacitors are all
fixed-value with just a small trimmer cap to calibrate the upper band
edge. All tuning adjustments are accomplished with about 30 turns of
the brass screw in the PTO design. If you use a brass screw PTO
please note that the frequency will "increase" as the screw is
inserted into the coil. One negative part of the PTO design is that
the tuning knob will move forward and backward about an inch (2.5
cm)from your front pannel as the frequency is changed. A photo of
this unit in its current state of construction is shown in the photo
section.
3) To test my crystal filter I built the BFO circuit from the
BITX20 design on a separate of circuit board and added the inductor
and variable capacitor in series with the crystal. This gave me a
very stable oscillator that could be tuned across the filter passband
to determine the shape factor. This signal was injected into the
input of the filter and a simple diode & capacitor type RF detector
was used with my voltmeter to measure the output. I do have a
frequency counter so I was able to determine the exact frequency that
was being output by my test oscillator. As the frequency was varied I
was able to plot the output voltage on a sheet of grid paper. I would
assume that you might do something similar in building your filter
using 8 MHz crystals. Remember that the center capacitor in the
filter is double the capacitance of each of the end capacitors. So
you will need 4 capacitors of the same value ( one on each end and two
in parallel in the middle ).
4) In my BITX20 and also in my BITX40 I changed the audio output
circuit from Farhan's original design. Since I usually use headphones
there was no need to have the audio level provided by the LM-386
integrated circuit. I used a simple LM-741 Op-Amp in place of the
LM-386. My op-amp runs a voltage gain of 100 that was achieved by
using a 100K feedback resistor and a 1K input resistor on the
inverting input. I will try to place a schematic of the op-amp
circuit on this web site later today.
Later I did add speaker capability to my BITX20 by building a
separate amplifier (it is in the external speaker case) using an NPN
transistor driving an NPN & PNP pair for about 1/2 watt of audio. I
will try to also add a schematic of that to this web site later today.
5) For the tap washers in Farhan's design I substituted 1/4 inch
wide slices of 1/2 inch (1.25 cm) PVC pipe. These measure about 5/8
inch ID and nearly 3/4 inch OD so they are slightly larger ID than the
tap washers but they worked fine. I already had the plastic pipe so I
did not need to make a trip to the hardware store for the tap washers.
A picture of these PVC coil forms is in the photos section under my
callsign. Note that I cut a slot in the side of my PVC coil forms to
make it easier to wind the inductors. This allows the wire to be
passed through the slot instead of threading each turn through the
center of a closed loop of plastic. Since the PVC does not affect the
magnetic properties of the coil, adding this slot has no affect on the
resulting inductance.

I hope this helps you and others that want to make alterations to
Farhan's excellent design. Like you I needed to make some changes to
accomodate the parts that I already had available for this project.

My BITX40 is not complete yet, but as I finish construction and
testing of each section I will try to post pictures and comments on
this web site. Like I said earlier, it really helps to have a working
BITX20 available for comparison testing with the sections of my BITX40
that are significently different from the original design.

Good luck on your effort,

Arv - K7HKL

Ashtar, I have followed the link to your site:-
www.phonestack.com/farhan
and the schematic around the LM386 still looks the same as before.

Duncan G4DFV

BITXers

There are several alternative ways to build various parts of the BITX
design. For my BITX40 I chose a PTO type oscillator for the VFO.
This uses a layout similar to that done by Jom - WA6OTP
<www.wa6otp.com&#92;pto.htm> for the mechanical construction, but is a BJT
based Clapp oscillator circuit with emitter-follower VFO buffer. A 32
tpi (turns per inch) brass screw is threaded into a coil of #28 wound
on a soda straw and covered in hot-melt glue. The present tuning
range is about +350 KHz for my version. This covers all of 40 Meters
(7.0 - 7.3 MHz) in 28 turns of the knob. I am still tweeking this to
try for 10 KHz per turn, but that is not quite working yet.

A picture has been posted (see PHOTOS in the BITX20 forum pages under
K7HKL) to show the mechanical design. A schematic has not yet been
finalized because the oscillator is prototype and still being modified
for tuning range and temperature stability.

K7HKL

Hi,

Please I do not have the 10MHz crystals to make the filter, but I
have 5 pieces of 8MHz crystals with this 8MHz crystals is possible

to

make the filter with new values of resistor and capacitor?

this kind of filter can be made with several x-tals.
For SSB usualy x-tals above 10 MHz are used, however, lower is also
possible.
The lower the x-tal frequency, the smaller the capacitors between
the x-tals must be.

modify the Bitx20 to Bitx40 is only to modify the Band Pass filter
and de oscillator?Somebody has this modification?

Because almost everything is broadband, it is possible to make it
for the band you want. Exact details: with a dipper and some
experiments you will find it out!
Best regards,
Chris, PA3CRX

The order for the 2nd round of components is now in. With any luck, they
arrive tomorrow and I despatch them to you tomorrow. Due to a shortage of
2N2219 at Viewcom I ordered the real 2N2218 from Mode Components. Slightly
cheaper too :-)

Just like last time, I have ordered two extra sets of components, comprising
all semiconductors, ten 10MHz crystals, trimmer capacitors and a 200pF
tuning capacitor. If anyone wants one of these two spare sets, the price is
exactly ?8, plus ?0.28 UK postage (or whatever the postage for 50g to your
country is, if you are outside the UK).

72/3 Hans G0UPL

Note that I have 20 spare 10MHz crystals, from my components order. Price is
?2.23 for 10 crystals, plus postage at cost.

73 Hans G0UPL

Please I do not have the 10MHz crystals to make the filter, but I
have 5 pieces of 8MHz crystals with this 8MHz crystals is possible to
make the filter with new values of resistor and capacitor?And to
modify the Bitx20 to Bitx40 is only to modify the Band Pass filter
and de oscillator?Somebody has this modification?

Thanks!

开云体育

I just measured the resonance frequency of ten 10 MHz
crystals. I found a set of four within 30 Hz and
another set of four within 45 Hz.

How does this compare to other peoples results?

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.

Note: these frequency counter readings are on my homebrew frequency counter
(
) which is installed in my 80/40m receiver
(). Previously in 30m
QRSS beacon experiments () I
built a simple 30m direct conversion receiver
() and calibrated the
frequency counter against the Moscow RWM timesignal on 9,996,000. My counter
was reading just over 1KHz too low at this frequency. So the measurements
above would need to be revised upwards by about 1KHz. But it's the relative
frequency which is important here anyway, and I haven't repeated the
calibration.

Did somebody already plot the passband shape of a
resulting 4 crystal filter?

How do you do that? Figure out the shape that is?

Farhan has spoken about theoretically determining the shape. I'd also like
to see experimental measurements. One way is to use a spectrum analyser with
tracking generator and very narrow bandwidths available. The filter shape
would appear directly on the screen. I built a spectrum analyser
(
) and someday I will make a tracking generator, but not yet (too many other
projects).

When I have time, I indend to build another logarithmic amplifier using the
excellent (but expensive) AD8307 chip. Using this with a voltmeter to
measure the logarithmic output, a frequency counter and a 30m VFO it would
be possible to take a series of measurements of the filter attenuation at
different frequencies and plot the curve. The log amp on my spectrum
analyser can be seen here:

/index.htm. You'll note that it's a very simple circuit. I think this will
provide a cheap way to obtain the passband curve.

72/3 de Hans G0UPL

- farhan wrote:

i am convinced that we need to add detailed test measurements for the
transceiver on the site. i have most of them in my log book. i will
post them soon.

I would welcome test measurements - two days of head scratching so
far! The RX is alive in my rig but not yet kicking! I have a lot of
BFO audible in the output also I have had to bypass the xtal filter
and the band pass filter to get any signal strength.

I'll tell you all this story just for fun. I had no joy with the
band pass filter and nearly threw the rig out of the window. Then I
realised that when I had "made" 2.2 pm out of 5 x 10pf caps I had
them in parralel and not series! Oh boy, the basic mistakes!

I try some more tomorrow.

Mark G0MGX



--- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:

Thanks for the additional information.

the correct schmatics are now at www.phonestack.com/farhan.

I checked again and

found

out that point 5 and 6 are stil wrong (not in accordance with the
data sheet, as noticed and posted by someone else).
I connected it correctly but an other person that follows the
schematic can have serious problems.
(if you make adjustments to your site, may be you can also add a
link to this yahoo group?).

The point is that I expected more output after the mixer. I am
always suspicious with that kind of coils (did I take the right

one,

did I make the correct connections, is it really working the way

it

should be) so I like to check something.

if you have already made the crystal filter, it is best that you

measure

and check the signal at the output Q12 (without the RF mixer

connected).
I will work on it today and add directly the next stages to
terminate the filter as good as possible. I hope the output will
then be incresed some more otherwise I do not end up with enough
power at the end (or am I pessimistic ;-) ).

have you tested the receiver yet? it is usually the recevier

that

comes

alive first.

The receiver works, while connecting a wire to Q3 I hear a lot

more

then with the wire connected to the mixer.

i am convinced that we need to add detailed test measurements

for

the

transceiver on the site. i have most of them in my log book. i

will post

them soon.

In general, voltages can be checked easily to find out roughly

that

the connections are correct and the correct values resistors are
mounted. Some general clues about what can be expected while
connecting a wire to a point or what voltage can be measured with
simple test gear would make it more complete indeed. May be

current

with and without oscilator on (for every stage) will avoid the

need

for more test equipment?
Adding too many measurement possibilities may be prevents a lot of
people building the design because they think it is all needed.
Doing the way you do now makes it important for everyone to
understand the circuit resulting in a higher level of radio
amateurs ;-)

Other builders comments?
Best regards,
Chris, PA3CRX

Thanks for the additional information.

the correct schmatics are now at www.phonestack.com/farhan.

I checked again and found
out that point 5 and 6 are stil wrong (not in accordance with the
data sheet, as noticed and posted by someone else).
I connected it correctly but an other person that follows the
schematic can have serious problems.
(if you make adjustments to your site, may be you can also add a
link to this yahoo group?).

The point is that I expected more output after the mixer. I am
always suspicious with that kind of coils (did I take the right one,
did I make the correct connections, is it really working the way it
should be) so I like to check something.

if you have already made the crystal filter, it is best that you

measure

and check the signal at the output Q12 (without the RF mixer

connected).
I will work on it today and add directly the next stages to
terminate the filter as good as possible. I hope the output will
then be incresed some more otherwise I do not end up with enough
power at the end (or am I pessimistic ;-) ).

have you tested the receiver yet? it is usually the recevier that

comes

alive first.

The receiver works, while connecting a wire to Q3 I hear a lot more
then with the wire connected to the mixer.

i am convinced that we need to add detailed test measurements for

the

transceiver on the site. i have most of them in my log book. i

will post

them soon.

In general, voltages can be checked easily to find out roughly that
the connections are correct and the correct values resistors are
mounted. Some general clues about what can be expected while
connecting a wire to a point or what voltage can be measured with
simple test gear would make it more complete indeed. May be current
with and without oscilator on (for every stage) will avoid the need
for more test equipment?
Adding too many measurement possibilities may be prevents a lot of
people building the design because they think it is all needed.
Doing the way you do now makes it important for everyone to
understand the circuit resulting in a higher level of radio
amateurs ;-)

Other builders comments?
Best regards,
Chris, PA3CRX

--- In BITX20@..., "n3ted" <tedkell@e...> wrote:

Did somebody already plot the passband shape of a resulting 4

crystal

filter?

How do you do that? Figure out the shape that is?

the shape is easy to figure out if you already know the crystal
parameters. the crystal parameters are easier to measure now thanks
to the G3UUR method. i have outlined it at
.

the essential idea is that a crystal filter looks like a capacitor
and an inductor in series (these are called motional capacitance and
motional inductance respectively). in addition to these, between the
leads of the crystal you will also be able measure a parallel
capacitance.

using the G3UUR method, you put each of the crystals into the
oscillator and measure its frequency. then you solder a 22pf or a
33pf in series with the crystal and measure the frequency shift. the
shift gives you a good approximation of the motional capacitance and
given the capacitance it is trivial to calculate the inductance
(given that we know the crystal's frequency). the parallel
capacitance is also approximated and the crystal is completely
modelled.

once you know the crystal parameters, you can spend a weekend
understanding the butterworth filter design. or you can use the
cookbook method in EMRFD like I did, or just use w7zoi program that
comes with his other book Introduction to RF Design.

using the my motional parameters, w7zoi did run it through his
program GPLA.exe and i have just uploaded the results to the
pictures folder.

i am including his comments that go with the picture below:
<snip>

The first file, ashhar01, part A, shows the
filter I designed with your motional L of 11.95 mH. I designed for
2200 Hz
bandwidth and a Butterworth response. Then the filter at part B
is a
more practical version of the same thing. It is much like the
filter that
you ended up building. My simulations suggest that is really is
worthwhile
to add the tuning capacitors at the ends though, for it produces a
much
smoother, ripple free response. The first analysis I did used
equal
terminations of 200 Ohms (perhaps 220) at each end and the response
was of
course text book. But the question remained -- what would the
response be
if the filter was terminated in other resistances. The file
ashhar02
shows what you get with a 50 Ohm source and a 200 Ohm load. This
is still
pretty good. The response is not nearly so good with 100 Ohms per
side,
which is about the characteristic Z0 of your amplifiers.

</snip>

- farhan

On Wed, 30 Jun 2004, vdberghak wrote:

The LF parts works fine (a pitty the schematic is not corrected with
the voltage/output of the lm386).

the correct schmatics are now at www.phonestack.com/farhan. i have run out
of bandwidth on . ther is no way i can access those
files now. just before i ran out of bandwidth, i did manage to put a
redirect on the home page. yo probably have te BITX20 page directly
bookmarked. which is why you are not being redirected to the new site.

If I add a sinus LF wave to the
microphone terminal, the shape looks simular on the colector.
However, as soon as I connect the coil of the balans mixer to it, it
becomes a-symetrical (one side is going to be clipped).

you need a 10mV signal at the base of the mic. this is usually too low to
be measured with an oscilloscope. your best bet is to actually connect a
mic and speak into it. if you can whistle (keeping your breath away from
the mic), it is a single tone-test. an extended 'aaaa' looks like a
three-tone test to me.

the other side is clipeed, because you note, the diodes in the mixer will
clamp the output through the attentuator. this is an expected behaviour.

If I put a lot of LF signal in it (looks heavily distorted, then I
get a maximum output(after the attenuater) of about 0.2 mw. (in 50
ohm). After reducing the LF signal to a point it looks normal, the
output power is very very less....
Did anyone look at the osciloscoop the way I did? Anyone measured
the output?

it is best to check the balanced modulator on its own first, without the
mic connected. you should be able to null the carrier at mid setting of
the preset and the 22pf trimmer. if that works, then you can move to the
audio stage.

typically, keeping the audio output of the mic amp connected to diode
modulator, you should see similar waveforms at the modulator input (where
the two transformer windings are shorted) and the output (the attentuator
pad) when using the oscilloscope at audio frequencies (keeping the time
base to about 10mSec per div).

as you have pointed out, the distortion is due to the non-linear nature of
the diodes. To measure the RF component alone, you should measure the
output through a hihg pass filter. for quick and dirty measurement,
connecte an RFC across the output of the attenuator and then connected the
oscilloscope.

if you have already made the crystal fitler, it is best that you measure
and check the signal at the output Q12 (without the RF mixer connected).
there is little that can go wrong in the Q12 and Q11. the only caveat is
that depending upon the exact frequency of the BFO, you might or might not
get SSB. If you are sitting in the middle of the filter's passband, you
will get DSB with audio roll-off at 1-2khz. but the enveolope will be
there to see.

have you tested the receiver yet? it is usually the recevier that comes
alive first. it gives you a good idea of how things are working.

i am convinced that we need to add detailed test measurements for the
transceiver on the site. i have most of them in my log book. i will post
them soon.

- farhan

The distortion I can imagine can be caused by one of the diodes, but
such low output at that moment?
After the next amp (before the x-tal filter, the maximum output is
about 1 mw (in 50 ohm). The reason is that I measure in 50 ohm is
that the load is in the mw. meter.
Thanks in advance for your comments,
Chris PA3CRX





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