Hi Chris,

Hi,
at this moment I spend hours getting the filter working for the IF
frequency of 4.9152 MHz.

Which band are you designing it for? 4.915 is too low for 14MHz SSB and sets
the VFO tuning quite high and prone to QSY/QRH (drifting). As I have read
over there, for SSB IFs over 8MHz are better and set the VFO on lower and
more stable frequencies. Crystals between 8 and 12MHz are easy to get here
in Europe, I can get 8, 8.86, 9.83, 10, 11, 11.059 and 12 for less than 0.75
euros each, there in PA you should be also able to do so...

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?

A way to know the filter shape is to connect a wideband noise generator or a
wobbulator to the filter input, an AM detector (diode and capacitor) to the
output and an oscilloscope (could be a PC audio oscilloscope thru the sound
card) to the AM detector. You'll see the ripple and the bell-like shape of
the filter passband. I have seen images in the net, one of them in the site
of PY2OHH, Miguel, It is in portuguese
but some friends are helping them to translate the pages into english...

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

I am not building the BITX, but I am enjoying this list and learning about
it anyway. All the parts but the IRF510 final amplifier are easy to get here
(and I stock most of them) so it is possible I will build it someday...

73, 72 de Juanjo, EA5CHQ-EC5ACA. EA-QRP #104, G-QRP #9742,
QRP-L #1662.

Juanjo Pastor
C/San Roque, 4-1???
46460 Silla
SPAIN

e-mail: ea5chq@...
web:
web del club:
Tel.: +034 96 120 17 67
Movil: 651 35 35 11

I just need confirmation about my frequency 'plan' table below,
is this correct in the meaning of 'practical' especially for 10

MHz,

that the VFO need to tune 0 ~ 0.4 MHz ?

Hi,
with the filter directly connected to the antenna you are already on
10 mHz!
What is the sense of making a SSB rig for a band that alouds NO SSB?
For 10 MHz you can use the same concept with an other frequency X-tal
filter you can shape for CW use.
Good luck,
Chris,

Charles

Just to make sure that all works as anticipated in your club demo of the spreadsheet program...I have attached two versions of the spreadsheet to this email. The one with the .sxc sufix is customized for Linux and OpenOffice Spreadsheet tools. The one with the .xls suffix is my original version written using Win-98 and MS-Excel. This way you can provide copies to your club members that will fit whatever computing platform they might be using.

Please feel free to distribute this program for any non-commercial use. I had fun developing the code, so maybe someone else will have fun using it.

For your own use...the sheet protection password is my callsign (all lower-case) so now you can customize the spreadsheet to include your club logo or name. Just remember to make your changes to a "copy" of the original so that if you make a mess of it you can always return to the pure original and start over (with a new copy of the original!). 8-)

73's
Arv - K7HKL
_._

I agree with all Jim's comments about the use of FET's salvaged from PSU's
etc in power amplifiers for bands 40m or below. I always like to use
"recycled" components wherever possible.

But when it comes to higher frequency amps, the IRF510 is in my opinion the
best choice available. A month or two I was considering a highly efficient
class E amp for 30m, for a /p rig. I wondered why the IRF510 was so popular
in QRP designs. Was it just fashion? Low cost (relatively)? So I read *many*
power FET datasheets to see if there was any better alternative, at ANY
price. Gate capacitance is an issue at higher frequencies, it must be as
small as possible. Similarly fast switching times are increasingly important
at higher frequencies. For best efficiency one wants low ON resistance. And
of course high power handling capability is essential.

Unfortunately, the choice of power FET necessarily involves some compromise
of these parameters. Larger device size means lower ON resistance and higher
power dissipation, but at the expense of higher gate capacitance and thereby
also slower speed. And so on. After all my searching, I was unable to find a
device that I considered offered a more optimum compromise of these
characteristics, for an efficient QRP HF amp, than the IRF510.

It therefore appears that this is THE best FET for QRP rigs, not just a
fashion or low cost, availability etc. All the more remarkable if there is
any truth in the story that I heard, about this FET originally being
designed for use switching car indicator lights. Or is this just urban
legend? Either way, long live the prince of FET's!

72/3 de Hans G0UPL

开云体育

one of the inherent problems with 10 MHz if is that it precludes the 10
MHz band. the IF will fall within the RF passband.

it might work if you used 14.318 MHz crystals for IF and used the 4 MHz
vfo to mix down to 10MHz IF.

You have to keep the IF, RF and VFO frequencies away from each other as
well as see to it their various (and particularly odd) multiples don't
match up.

For instance, you used a 9Mhz IF for an 18 MHz design. The second harmonic
of the BFO will appear as a tunable signal in the receiver. The VFO will
also appear as a quickly tuned spur.

W7ZOI has a program called spurtune.exe that is ideal to work these spur
resposnes out.

i am not sure about the copyrights on these programs. if they are
distributable, then i can upload them to our folders for everybody to use
them. they are very useful, all of them.

- farhan

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!