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k7hkl_arv <arvevans@...>

Hello again Chris,

Crystals between 8 and 12MHz are easy to get here
in Europe,

They are also cheap available by one of the group members but (as
mentioned by one of the other group members) some persons have a
kind of brain damage that force us to use what we have. Spending
hours to get some used parts from an old PCB cost ofcourse more then
buying new but now I can say: 'I build this transceiver from scrap
and components that I had collected in the past'.
An other point of view; by using these alternatives, you learn a lot
about parameters and the circuit!
(If I do not get it working the way I want to, may be I will go to
the 10 MHz IF ;-) ).

If you want to follow the "from scrap" route, you'd better use 8.86 MHz
crystals from defunct color TV sets or the 14.318 MHz ones from old and/or
defunct PC motherboards...

I am not building the BITX, but I am enjoying this list and

learning about

I appreciate your comments, as mentioned above, search in your junk
box and build your own tranceiver based on the BITX20.

Chris, PA3CRX

As I said before, I do own almost all of the parts or can get them easily,
the hard one here is the IRF510 but I have a few of them from scrap... I am
into a 40m CW VXO TX, when I end it maybe I will start the 20 meter SSB
project...

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

Hans I wonder if you would like to confirm one or two items
which are not clear to me...

No problem! My favourite varicap is a standard 5mm red LED. Have a look at
my 30m QRSS beacon project
which used one for the frequency shifting to produce DFCW and
slow-hellscreiber modes. Far too many people get stuck ordering components
for a project, when they can't find the specified varicap. Varicaps are
components which seem to go in and out of fashion quite quickly. In most of
those cases, they could easily substitute with something else, or even just
a simple diode. Don't forget even in the BITX20 we're using a 36V zener
diode for the VFO fine tuning! A "real" varicap diode will have more
precisely defined and reproduceable capacitance limits but in the majority
of homebrew QRP circuits, that isn't very important. One exception is if you
want a large capacitance, e.g. the BB212 varicap which seems to be
increasingly hard to find. Even in this case, many times the circuit can
easily be redesigned for a lower capacitance range.

1. that the volts into the 4060 are 12V

Errr.... No. I used 12V on the "varicap" but only a +5V supply to the 4060.
The reason I say "err" is that according to the datasheet, the "typical"
maximum clock frequency of the old 4000-series CMOS version of this IC is
7MHz on a 5V supply (no "maximum" maximum clock frequency is indicated).
Ooops. But it did work Ok for me anyway despite being violation of the
datasheet parameters. At higher supply voltages the 4060 has typical 16MHz
at 10V and 24MHz at 15V. So you would be better off using +12V supply anyway
;-) Even better, use the modern 74HC4060, at 5V supply you're looking at
over 30MHz for the max count freq. But you'd need 5V supply for 74HC.

2. that the 14MHz xtal could be changed for one of the 10MHz
xtal already obtained ( through you ) for the project ...

Sure, why not. Any crystal should exhibit the same pullable effect with
parallel capacitance. Although some are more "pullable" than others and as
you might expect, in general you will find that the higher the frequency the
greater the shift (in absolute KHz terms). From my "crystal penning"
experiments and those of Dave WA4QAL there appears to be some evidence that
physically smaller crystals are more shiftable, e.g. we obtained more shift
on HC49 style crystals than the larger slab in an HC6 case. The same might
apply to pulling with capacitors, but I don't know. The 14MHz crystal I used
was the common HC49-cased variety.

While we're on the subject of crystals, if you want to move them by more
than a bit of capacitance will accomplish, you can get many KHz lower by
removing the case and painting the crystal with ink! See my page about this:
. My 1-valve CW tx for
80/40m () contains two
"penned" crystals: 3.558 (originally 3.579) and 7.010 (originally 7.030).
See also the first modification I made to the 30m QRSS beacon I mentioned
above, , which was
to add a 10.140 crystal. I guess that this crystal must have been custom
manufactured at some point but it wasn't very accurate, 4KHz to high. A
single ink dot on its surface was enough to bring it down to 10.142 which
was about perfect for what I wanted.

And if you want to go the other way and increase the frequency of a crystal?
Grind it and grind it, then grind some more. For this you need a larger
crystal (e.g. FT-243 style), the HC49 is just too small and you wouldn't be
able to remount if afterwards. See
for some interesting grinding
experiments recently undertaken by Dave WA4QAL.

3. could I / a student use ugly construction for the test
project ???

Yes definitely! I used a scrap of plain matrix board but "ugly" is fine too!

73 de Hans G0UPL

Following Farhan's mention of my frequency counters...


this one is a full 8-digit counter.

On the other hand, you can throw together something really fast with 8=LED
binary readout and only 2 chips:



This reads only 0 - 99.5KHz, the MHz and 100KHz aren't shown. However,
please note that is is quite easy to fit a switch to select a different
division of the timebase, in order to obtain a MHz reading. Look at the
website of Onno PA2OHH whose ideas my
counter is based on.

73 Hans G0UPL

Hi Juanjo,

> 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.

There are more reasons for making the filter in the range

---

Do you Yahoo!?
Get it on your mobile phone.

the VFO of BITX20 has an interesting story. it is actually my inductance
meter!
looking at the VFO, if you removed the trimmer, it becomes a test
oscillator that iuse at all times. this idea is due to W7AAZ (Bill
Carver).
you can quickly assemble a frequency counter like one of the several shown
by Hans.
To measure an inductance, solder the the coil into the VFO circuit,
measure the frequency. The capacitance is well established, from there
calculate the inductance.
i had written a few lines code in C (i think it is posted it its entirity
on rec.radio.amateur.homebrew). that helped me calculate it quickly.
the test oscillator also works as acrystal oscillator (solder a crystal
in place of the coil) to measure and match the crystals.

- farhan

Hi all

I was at my local radio club the other night and was discussing the
possibility of using the BITX on RTTY .. This prompted the following
responce from one of the members ...

"The elegant way for RTTY is to have a carrier, and this is shifted
for one of the tones. A small amount of capacity added across an
oscillator is the usual way, switched by the RTTY signal coming from
(say) the teleprinter contacts - or today a computer output from the
com port. This results in a purer outgoing signal than two tones into
the mike socket, as the amplitude of the tones is identical, which
does not happen when tones in the mike socket is used. (Check the
output power of the TX on mark, and then space, when using audio in
the mike. Not the same!!"

So this prompted me to look for information on the varicap ...

I came across this site :-


I have printed off all of the data and this will be another display
project to show members ( or have them build it and then discover )
as stated in the article "any diode is a varicap diode".

Hans I wonder if you would like to confirm one or two items which
are not clear to me...
1. that the volts into the 4060 are 12V
2. that the 14MHz xtal could be changed for one of the 10MHz xtal
already obtained ( through you ) for the project ...
3. could I / a student use ugly construction for the test project ???

This whole BITX project is enabling so many teaching side lines that
the students will not realise that they are learning so much.

73 all

Charles G4VSZ

Hi Juanjo,

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.

There are more reasons for making the filter in the range 10 to 12
MHz, one for example is that lower IF x-tal ladder filters are
difficult for SSB, for CW they seems to be great.
My BITX will be for the 18 MHz band so my LO will be in the 13 MHz.
I will try a VXO, covering the whole phone band.

Crystals between 8 and 12MHz are easy to get here
in Europe,

They are also cheap available by one of the group members but (as
mentioned by one of the other group members) some persons have a
kind of brain damage that force us to use what we have. Spending
hours to get some used parts from an old PCB cost ofcourse more then
buying new but now I can say: 'I build this transceiver from scrap
and components that I had collected in the past'.
An other point of view; by using these alternatives, you learn a lot
about parameters and the circuit!
(If I do not get it working the way I want to, may be I will go to
the 10 MHz IF ;-) ).

I am not building the BITX, but I am enjoying this list and

learning about

I appreciate your comments, as mentioned above, search in your junk
box and build your own tranceiver based on the BITX20.

Chris, PA3CRX

开云体育

A quick frequency calculation spreadsheet for the BITX-xx has been placed in the FILES section under K7HKL/BITX....

This should help resolve some of the questions regarding alternative IF Filter frequency possibilities.?

Arv - K7HKL

Hi all

I note that the post has separated part of the url from the web page
mentioned - let's try again ----

www.web-ee.com/Schematics/Inductance%20Meter/Inductance%20Meter.htm

You need all without a break between Inductance% and 20Meter.htm

I hope this helps you to find the page...

Charles

Hi all

Saw this page whilst searching the web


20Meter.htm

It describes the construction of a simple inductance meter which is
an add on to a digital multi meter DMM. Range possible 3 micro H to
5 milli H so will be good for many of the inductors needed for the
project - to at least know that you are in the right ball park !!!

The heart of the project is just a single chip 74HC132 and a LM7805
to provide voltage regulation.

A friend is already starting the construction to day so I will leave
more feed back in due course.

Regards and 73
Charles G4VSZ

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