|
MILAREPA@.............
It would appear from your chart that the higher frequency crystals may not be oscillating, or that your frequency counter may not be capable of counting above 10 MHz.
Lets explore the first possibility (that the higher frequency crystals may not be oscillating):
? (1)? Check the RF output of your crystal oscillator using a simple diode & capacitor RF detector and a high impedance DC volt meter.? If there is RF present it should be in the range of 4 to 12 volts.
? (2)? If the transistor you are using for the Crystal oscillator is not capable of operating at 10 MHz or above, it may be not oscillating with the higher frequency crystals.? The solution for this is to use a better transistor.? In the US we have 2N2222 and 2N3904 available for very reasonable prices so this is what I use for most of my HF work.? These devices are rated to 150 MHZ, and will usually oscillate at even higher frequencies.
? (3)? In your crystal oscillator circuit it is possible that one or more of the capacitors you are using is not the capacitance value that you think it is.? Check each capacitor on a capacitor tester to determine its actual measured capacitance.? Then verify on the schematic and parts list that you are using the correct value for the design.? If you do not have a capacitance meter, you can use the simple AC transformer and Digital VoltMeter (DVM) method outlined in one of my earlier emails to the forum.? A schematic and picture of this is also available in the PHOTOS section of the forum archives (look under my call sign, " K7HKL " )
? (4)? The DC bias may not be correct in your crystal oscillator circuit.? Check the voltages on the oscillator transistor using a high impedance voltmeter.? The difference between base and emitter voltages should be approximately 0.7 volts for silicon transistors (it will be about 0.3 volt for germanium transistors, but I have not seen one of those antiques for several years).? The collector voltage should be about 1/2 the supply voltage.? If your oscillator design has an emitter resistor you can measure the voltage drop across that device and with a little math determine the collector current of your oscillator transistor.
? (5) It is possible that one or more of the resistors in your crystal oscillator circuit may not be close enough to the design value.? A quick ohm meter check on each resistor should detect this situation.? The resistor values are not particularly critical, but they should be within 10 to 20 percent of those indicated in Farhan's design.?
Now, the "possibilities" for your counter being the problem:
? (1)? Many years ago I built a number of frequency counters using 7490 dividers and 7447 LED drivers.? One of the major problems experienced with those circuits was a lack of HF sensitivity in the input amplifier and count gating circuit.? Designing a frequency counter to have a very high input impedance and flat frequency response over a wide bandwidth is nearly impossible.? I finally resorted to engineering for a lower input impedance and using a very broadband input amplifier to drive my 7400 count gating circuit.?
? (2)? One mistake that is prevalent is to use a low impedance coaxial lead as the input to your frequency counter but configure the counter for high impedance input.? Obviously this is a contradiction in impedances.? If you are doing this you can try "terminating either end of your counter input coax with a low impedance (non-inductive) resistor.? Start with about 470 ohms and work up or down from there.? An alternative might be to use a very small capacitor (about 10 pf) in series between the counter input cable and the circuit under test.? This lets the counter see a higher impedance, and does not disturb the circuit-under-test as much by loading it with whatever input cable impedance you are using on your counter.
? (2)? If you have a signal generator that will go higher than 10 or 12 MHz you could verify that your counter is capable of reliably counting to those higher frequencies.? At the same time you might want to "calibrate" the sensitivity of your counter so that you will know how much RF voltage it takes at 5, 10, & 20 MHz to result in a reliable count of that frequency.? Do this by using a carbon potentiometer to attenuate the input to your counter and use your diode detector and high impedance voltmeter to measure the RF voltage level at which counting becomes unreliable.? Be sure to use the same test leads on your counter for both sensitivity calibration and for measurements on your BITX20 circuits.
Regarding the use of 3.579 MHz crystals as IF Filters:
Using 3.579 MHz crystals as IF Filters is an interesting experiment.? The older and larger sized crystals that I have available exhibit much different characteristics than those of smaller 10 MHz crystals.? I was unable to obtain consistent motional parameters from my test setup when using 3.579 MHz units, but the 10 MHz crystals worked first time.? For an experiment I selected a pair of 3.579 crystals that were 1.4 KHz different in frequency and used these to build up a half-lattice filter.? The half-lattice design requires use of a toroid transformer, and here I did use a ferrite core for that purpose.? If you don't have a suitable ferrite core available you can try the Tap Washer cores that Farhan suggests, but at this time I have no data on what might be the proper number of turns.?? I found the half-lattice filter using 3.579 MHz crystals to be adequate for SSB work.? However, the use of a half-lattice filter does not readily adapt to the bi-directional design used in the BITX20, so this may not be a good solution.
It is also possible to use a single 3.579 MHz crystal in series with the signal path as the IF filter in simple superhetrodyne receivers.? Again this becomes problematic if one tries to use this arrangement in a bi-directional design like the BITX20, because the terminating resistor is on the wrong end of the crystal in transmit mode.? I suppose one could do some sort of diode switching of either the whole crystal filter or just the terminating resistor, but that is rapidly getting beyond the simple nature of the original BITX design objective.
Here is a thought that I have been playing with for several days...Would it be possible to use a single 10 MHz (or other frequency) crystal as the IF filter in the BITX-xx design and simply center the carrier in the IF passband.? This would result in DSB (Double Sideband) instead of SSB (Single Sideband) transmission, but it might work to get a system on the air.? One possible problem with this is that single-crystal IF filters tend to be very narrow banded, in the order of 200 HZ, and have a steep roll off on one sideband only.? I am not sure what this characteristic would do to the audio quality of a DSB signal.? I guess that someone has to try it for us to know for sure...?
OK, I have probably covered much more than you wanted to know.
I hope this helps.
Arv - K7HKL
_._?
On Fri, 2004-07-16 at 04:30, MILAREPA wrote:
toggle quoted message
Show quoted text
Dear forum,
?
==About Crystal Measurements==
At the time I mail to BITX about this subject,
'actually' I was using a 3.579545 MHz crystal, that available
at my junkbox and drifting is in this frequency.
( not 12 MHz... ).
?
After that email I buy some crystal,
each 10.00 MHz, 12.00 MHz, 12.288 MHz, and 14.00 MHz.
and make some test for each crystal, using my vfo and socket
as?Hans's suggest, then connect / monitor at :
shortwave rx, counter 8 leds, counter one-7segment, and
rs232 - pc monitor ( this rs232 is part of one-7segment counter's add on )
here are the results:
?
?
The measurements stop at 10.00 MHz on 8 led cntr,
since the 8 led accuracy is 10.xxx MHz, and I need to
check them on rs232-pc but happened not displayed.
?
Please suggest what is possible here.
-Why for 10 MHz higher the circuit doesn't works normally ?
I have read that for a higher frequency, the vfo gain could be drop.
-Does vfo design limit is at 10 MHz ?
-How to fix this ?
?
Thanks.
|
Hi,why the intention to add one x-tal as a filter if you want to generate DSB? Just remove the current IF filter from the design and you have already DSB! By doing this, you can also investigate (for example during receiving) the impact of the IF filter. If the received signal looks good without filter and is horrible with the filter, someting is wrong with the shape or position of the passband. Good lock, Chris. Would
it be possible to use a single 10 MHz (or other frequency) crystal as the IF filter in the BITX-xx design and simply center the carrier in the IF passband. This would result in DSB (Double Sideband) instead of SSB (Single Sideband) transmission, but it might work to get a system on the air. One possible problem with this is that single-crystal IF filters tend to be very narrow banded, in the order of 200 HZ, and have a steep roll off on one sideband only. I am not sure what this characteristic would do to the audio quality of a DSB signal. I guess that someone has to try it for us to know for sure...?
|
Chris, & others...
Please take a closer look at the BITX IF string without any crystal filter.? There would be no control of the passband and thus no way to tune a specific frequency, other than as a very broadband DC RX with a converter ahead of it.? There would also be little rejection of image frequencies.? The crystal filter is the only frequency determining part of the IF amplifier string, so at least some minimal bandwidth control is probably necessary.? I have to admit that my first working receive-only mock-up of the BITX20 did use a pair of 10.7 IF transformers that were peaked at 10.0 MHZ in place of the crystal filter.? It sort of worked (very, very broad tuning and prone to oscillation) so I purchased the necessary 10 MHz crystals and rebuilt it per Farhan's instructions.
Use of a single-crystal IF filter is interesting for QRP activists who may not need SSB.? The IF filter loss would be significantly less than the 10 to 12 db of the ladder filter, and with a variable capacitor (maybe a varicap) it should be possible to adjust the bandwidth to some extent.? Farhan & myself have discussed using the BITX for other modes, including CW by using a computer sound card or by making the microphone amplifier into a keyed oscillator (probably easier than unbalancing the modulator to get a keyed carrier).
The most intriguing part of the BITX design philosophy is that it is relatively easy and inexpensive? to duplicate Farhan's design, and then to customize it for whatever special features you might want to try. Farhan uses his BITX on CW and PSK-31 as well as SSB, so we know it is capable of those modes.? Listed below are a few of the more obvious modifications for the basic design:
(1)? Consider the possibility of adding VOX by using a small relay for the T/R changeover and driving that relay with an amplified and rectified portion of the microphone audio.? Anti-vox could be incorporated by integrating a small portion of the RX audio (in proper phase) with the VOX audio amplification.? For CW the same VOX circuitry could automate RX - TX changeover.
? (2)? If you use computer driven modes of operation, you should probably include a connector for your computer on the back of your BITX-xx.? This connector might include the coupling attenuators that are necessary to bring the sound card output down to the correct level to match your microphone amplifier input, as well as tapping the RX audio ahead of the volume control so that adjusting speaker volume would not disturb your computer RX signal level.
? (3)? Adding a simple FWD & REF power meter or SWR meter seems obvious and rather easy to do.? The same meter could also be used as an audio-derived S-Meter with a one-transistor amplifier and a couple of diodes.
? (4)? Depending on the type and impedance of your antenna, it might be possible to include the antenna tuner inside the BITX enclosure for a nearly self-contained station.
? (5)? There are many options for the VFO, even building two VFOs for offset frequency operation.? For my BITX40 I built a PTO instead of using the two-capacitor design of the BITX20.? If one has built a DDS (Direct Digital Synthesis) unit, then that could become the VFO for your BITX.
? (6)? At least one BITX20 builder has shown pictures of his unit that incorporates an LCD frequency display, and another has shown his BITX with either 7-segment LED and /or binary frequency displays.?
? (7)? While Farhan's original design does incorporate a linear amplifier section, it is possible to substitute any of several good linear amplifier circuits ( even a tube-type linear if you have one lying around ! ).? I expect to soon hear of BITX designs that run much more power using combinations of parallel and push-pull IRF510 finals.
This amazing potential for altering and/or augmenting the basic unit is part of the magic associated with Farhan's original design.? Maybe we should start a "BITX MODIFICATIONS" sub-section as part of the forum...?? Hans, is it possible ( or even advisable ) to build a MODIFICATIONS sub-directory in the FILES section of BITX20@... that would support multiple users adding their circuits to that area?
73's
Arv - K7HKL
_._
On Sat, 2004-07-17 at 05:03, vdberghak wrote:
toggle quoted message
Show quoted text
Hi,why the intention to add one x-tal as a filter if you want to
generate DSB?
Just remove the current IF filter from the design and you have
already DSB!
By doing this, you can also investigate (for example during
receiving) the impact of the IF filter.
If the received signal looks good without filter and is horrible
with the filter, someting is wrong with the shape or position of the
passband.
Good lock,
Chris.
>Would
> it be possible to use a single 10 MHz (or other frequency) crystal
as
> the IF filter in the BITX-xx design and simply center the carrier
in the
> IF passband.? This would result in DSB (Double Sideband) instead
of SSB
> (Single Sideband) transmission, but it might work to get a system
on the
> air.? One possible problem with this is that single-crystal IF
filters
> tend to be very narrow banded, in the order of 200 HZ, and have a
steep
> roll off on one sideband only.? I am not sure what this
characteristic
> would do to the audio quality of a DSB signal.? I guess that
someone has
> to try it for us to know for sure...?
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I'm wondering, in a quiet, museing, sort of way, whether its a
reasonable prospect to use the IF strip as a driver to VHF using a
transverter in place of the PA and RX BPF. I have suitable
transverters to try it with but first I have to build the BITX.
A good idea, if its possible, to add a MODS section. I guess that
no one is going to build their second BITX without adding
personality to the build.
atb Mike W
--
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Show quoted text
On 17 Jul 04, at 11:31, Arv Evans wrote: --=-eSRYBxmSXrAkn9U7Gr+H
Content-Type: text/plain
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Chris, & others...
Please take a closer look at the BITX IF string without any crystal
filter. There would be no control of the passband and thus no way to
tune a specific frequency, other than as a very broadband DC RX with a
converter ahead of it. There would also be little rejection of image
frequencies. The crystal filter is the only frequency determining
part of the IF amplifier string, so at least some minimal bandwidth
control is probably necessary. I have to admit that my first working
receive-only mock-up of the BITX20 did use a pair of 10.7 IF
transformers that were peaked at 10.0 MHZ in place of the crystal
filter. It sort of worked (very, very broad tuning and prone to
oscillation) so I purchased the necessary 10 MHz crystals and rebuilt
it per Farhan's instructions.
Use of a single-crystal IF filter is interesting for QRP activists who
may not need SSB. The IF filter loss would be significantly less than
the 10 to 12 db of the ladder filter, and with a variable capacitor
(maybe a varicap) it should be possible to adjust the bandwidth to
some extent. Farhan & myself have discussed using the BITX for other
modes, including CW by using a computer sound card or by making the
microphone amplifier into a keyed oscillator (probably easier than
unbalancing the modulator to get a keyed carrier).
The most intriguing part of the BITX design philosophy is that it is
relatively easy and inexpensive to duplicate Farhan's design, and
then to customize it for whatever special features you might want to
try. Farhan uses his BITX on CW and PSK-31 as well as SSB, so we know
it is capable of those modes. Listed below are a few of the more
obvious modifications for the basic design:
(1) Consider the possibility of adding VOX by using a small relay
for
the T/R changeover and driving that relay with an amplified and
rectified portion of the microphone audio. Anti-vox could be
incorporated by integrating a small portion of the RX audio (in proper
phase) with the VOX audio amplification. For CW the same VOX
circuitry could automate RX - TX changeover.
(2) If you use computer driven modes of operation, you should
probably include a connector for your computer on the back of your
BITX-xx. This connector might include the coupling attenuators that
are necessary to bring the sound card output down to the correct level
to match your microphone amplifier input, as well as tapping the RX
audio ahead of the volume control so that adjusting speaker volume
would not disturb your computer RX signal level.
(3) Adding a simple FWD & REF power meter or SWR meter seems
obvious
and rather easy to do. The same meter could also be used as an
audio-derived S-Meter with a one-transistor amplifier and a couple of
diodes.
(4) Depending on the type and impedance of your antenna, it might
be
possible to include the antenna tuner inside the BITX enclosure for a
nearly self-contained station.
(5) There are many options for the VFO, even building two VFOs for
offset frequency operation. For my BITX40 I built a PTO instead of
using the two-capacitor design of the BITX20. If one has built a DDS
(Direct Digital Synthesis) unit, then that could become the VFO for
your BITX.
(6) At least one BITX20 builder has shown pictures of his unit that
incorporates an LCD frequency display, and another has shown his BITX
with either 7-segment LED and /or binary frequency displays.
(7) While Farhan's original design does incorporate a linear
amplifier section, it is possible to substitute any of several good
linear amplifier circuits ( even a tube-type linear if you have one
lying around ! ). I expect to soon hear of BITX designs that run much
more power using combinations of parallel and push-pull IRF510 finals.
This amazing potential for altering and/or augmenting the basic unit
is part of the magic associated with Farhan's original design. Maybe
we should start a "BITX MODIFICATIONS" sub-section as part of the
forum...? Hans, is it possible ( or even advisable ) to build a
MODIFICATIONS sub-directory in the FILES section of
BITX20@... that would support multiple users adding their
circuits to that area?
73's
Arv - K7HKL
_._
On Sat, 2004-07-17 at 05:03, vdberghak wrote:
Hi,why the intention to add one x-tal as a filter if you want to
generate DSB? Just remove the current IF filter from the design and
you have already DSB! By doing this, you can also investigate (for
example during receiving) the impact of the IF filter. If the
received signal looks good without filter and is horrible with the
filter, someting is wrong with the shape or position of the
passband. Good lock, Chris.
Would
it be possible to use a single 10 MHz (or other frequency) crystal
as
the IF filter in the BITX-xx design and simply center the carrier in the
IF passband. This would result in DSB (Double Sideband) instead of SSB
(Single Sideband) transmission, but it might work to get a system on the
air. One possible problem with this is that single-crystal IF filters
tend to be very narrow banded, in the order of 200 HZ, and have a steep
roll off on one sideband only. I am not sure what this characteristic
would do to the audio quality of a DSB signal. I guess that someone has
to try it for us to know for sure...?
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Chris, & others...<BR>
<BR>
Please take a closer look at the BITX IF string without any crystal
filter. There would be no control of the passband and thus no
way to tune a specific frequency, other than as a very broadband DC RX
with a converter ahead of it. There would also be little
rejection of image frequencies. The crystal filter is the only
frequency determining part of the IF amplifier string, so at least
some minimal bandwidth control is probably necessary. I have to
admit that my first working receive-only mock-up of the BITX20 did use
a pair of 10.7 IF transformers that were peaked at 10.0 MHZ in place
of the crystal filter. It sort of worked (very, very broad
tuning and prone to oscillation) so I purchased the necessary 10 MHz
crystals and rebuilt it per Farhan's instructions.<BR> <BR> Use of a
single-crystal IF filter is interesting for QRP activists who may not
need SSB. The IF filter loss would be significantly less than
the 10 to 12 db of the ladder filter, and with a variable capacitor
(maybe a varicap) it should be possible to adjust the bandwidth to
some extent. Farhan & myself have discussed using the BITX
for other modes, including CW by using a computer sound card or by
making the microphone amplifier into a keyed oscillator (probably
easier than unbalancing the modulator to get a keyed carrier).<BR>
<BR> The most intriguing part of the BITX design philosophy is that it
is relatively easy and inexpensive to duplicate Farhan's design,
and then to customize it for whatever special features you might want
to try. Farhan uses his BITX on CW and PSK-31 as well as SSB, so we
know it is capable of those modes. Listed below are a few of the
more obvious modifications for the basic design:<BR> <BR>
(1) Consider the possibility of adding VOX by using a small
relay for the T/R changeover and driving that relay with an amplified
and rectified portion of the microphone audio. Anti-vox could
be incorporated by integrating a small portion of the RX audio (in
proper phase) with the VOX audio amplification. For CW the same
VOX circuitry could automate RX - TX changeover.<BR>
<BR>
(2) If you use computer driven modes of operation, you
should probably include a connector for your computer on the back of
your BITX-xx. This connector might include the coupling
attenuators that are necessary to bring the sound card output down to
the correct level to match your microphone amplifier input, as well as
tapping the RX audio ahead of the volume control so that adjusting
speaker volume would not disturb your computer RX signal level.<BR>
<BR> (3) Adding a simple FWD & REF power meter or SWR
meter seems obvious and rather easy to do. The same meter could
also be used as an audio-derived S-Meter with a one-transistor
amplifier and a couple of diodes.<BR> <BR> (4) Depending
on the type and impedance of your antenna, it might be possible to
include the antenna tuner inside the BITX enclosure for a nearly
self-contained station.<BR> <BR> (5) There are many
options for the VFO, even building two VFOs for offset frequency
operation. For my BITX40 I built a PTO instead of using the
two-capacitor design of the BITX20. If one has built a DDS
(Direct Digital Synthesis) unit, then that could become the VFO for
your BITX.<BR> <BR> (6) At least one BITX20 builder has
shown pictures of his unit that incorporates an LCD frequency display,
and another has shown his BITX with either 7-segment LED and /or
binary frequency displays. <BR> <BR> (7) While
Farhan's original design does incorporate a linear amplifier section,
it is possible to substitute any of several good linear amplifier
circuits ( even a tube-type linear if you have one lying around !
). I expect to soon hear of BITX designs that run much more
power using combinations of parallel and push-pull IRF510 finals.<BR>
<BR> This amazing potential for altering and/or augmenting the basic
unit is part of the magic associated with Farhan's original
design. Maybe we should start a "BITX MODIFICATIONS"
sub-section as part of the forum...? Hans, is it possible ( or
even advisable ) to build a MODIFICATIONS sub-directory in the FILES
section of BITX20@... that would support multiple users
adding their circuits to that area?<BR> <BR> 73's <BR> Arv - K7HKL<BR>
_._<BR> <BR> On Sat, 2004-07-17 at 05:03, vdberghak wrote: <BLOCKQUOTE
TYPE=CITE>
<FONT COLOR="#737373"><I><TT>Hi,why the intention to add one x-tal
as a filter if you want to <BR> generate DSB?<BR> Just remove the
current IF filter from the design and you have <BR> already
DSB!<BR> By doing this, you can also investigate (for example
during <BR> receiving) the impact of the IF filter.<BR> If the
received signal looks good without filter and is horrible <BR>
with the filter, someting is wrong with the shape or position of
the <BR> passband.<BR> Good lock,<BR> Chris.<BR> <BR>
>Would<BR> > it be possible to use a single 10 MHz (or other
frequency) crystal <BR> as<BR> > the IF filter in the BITX-xx
design and simply center the carrier <BR> in the<BR> > IF
passband. This would result in DSB (Double Sideband) instead
<BR> of SSB<BR> > (Single Sideband) transmission, but it might
work to get a system <BR> on the<BR> > air. One possible
problem with this is that single-crystal IF <BR> filters<BR> >
tend to be very narrow banded, in the order of 200 HZ, and have a
<BR> steep<BR> > roll off on one sideband only. I am not
sure what this <BR> characteristic<BR> > would do to the audio
quality of a DSB signal. I guess that <BR> someone has<BR>
> to try it for us to know for sure...?<BR> </TT><BR>
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Arv Listed below are a few of the more obvious
modifications for the basic design: All good points. This BITX20 reflector has been very interesting so far, and will continue to get even more interesting as the number of completed projects increases and people start working on modifications. Hans, is it possible ( or even advisable ) to build a
MODIFICATIONS sub-directory in the FILES section
of BITX20@... that would support
multiple users adding their circuits to that area? I think, both possible AND advisable. I am not an expert with Yahoo groups so I don't know the exact procedure, nor do I know if the group is configured so that it has to be done by me or it can be done by any member. I don't have internet access at home over the weekend so will wait until Monday to check. Meanwhile If you know how to do it, go ahead! 73 to all Hans G0UPL
|
Hans I think that either yourself or Farhan will have to build any "group writable directory", if it is even supported by Yahoo. In building my K7HKL directories in the Files and Photos sections I do not recall seeing any option where a non-administrator for the group could make those directories group writable. If you do provide group writable subdirectories for specific subject content it may be necessary to set up some guidelines to help define just what is expected and/or acceptable in these special directories That sounds like a possible administrative nightmare! I'm now wondering if it was such a good idea? ;-/ Hey! The person who contemplated using a BITX20 to drive a VHF transverter is really thinking. That opens up a whole new set of modifications that I had not considered. Why stop at VHF though? Why not VHF, UHF, and even microwave with a BITX as the baseband system? 73's Arv _._ --- In BITX20@..., Hans Summers <Hans.Summers@t...> wrote:
Arv
Listed below are a few of the more obvious
modifications for the basic design: All good points. This BITX20 reflector has been very interesting so
far, and will continue to get even more interesting as the number of completed
projects increases and people start working on modifications.
Hans, is it possible ( or even advisable ) to build a
MODIFICATIONS sub-directory in the FILES section
of BITX20@Y... that would support
multiple users adding their circuits to that area? I think, both possible AND advisable. I am not an expert with Yahoo groups so I don't know the exact procedure, nor do I know if the group is
configured so that it has to be done by me or it can be done by any member. I don't have internet access at home over the weekend so will wait until
Monday to check. Meanwhile If you know how to do it, go ahead!
73 to all
Hans G0UPL
|
On 18 Jul 04, at 5:20, Arvid Evans wrote: Hey! The person who contemplated using a BITX20 to drive a VHF
transverter is really thinking. That opens up a whole new set of
modifications that I had not considered. Why stop at VHF though? Why
not VHF, UHF, and even microwave with a BITX as the baseband system?
Wow !. Thanks Arv :-) vy 73 de G8NXD, Mike W --
|
Hi!
?
Arv,
?
Baseband......
?
This is good thinking. I was wondering on a 2.5Mhz If for BITX and 10Mhz xtal clock for?detection and rest thru SDR soft. Only a couple of more diodes to add (I Q Mixer), another balun for phase splitter, 74HC74 for osc signals.
?
Should not be a problem on lower bands even with a? L/C VFO for conversion.
?
This?place really got the grey matter working.
?
73
?
Rahul VU3WJM
?
?
?
Arvid Evans wrote:
Hans
I think that either yourself or Farhan will have to build any "group
writable directory", if it is even supported by Yahoo.? In building my
K7HKL directories in the Files and Photos sections I do not recall
seeing any option where a non-administrator for the group could make
those directories group writable.
If you do provide group writable subdirectories for specific subject
content it may be necessary to set up some guidelines to help? define
just what is expected and/or acceptable in these special directories
That sounds like a possible administrative nightmare!? I'm now
wondering if it was such a good idea?? ;-/
Hey!? The person who contemplated using a BITX20 to drive a VHF
transverter is really thinking.? That opens up a whole new set of
modifications that I had not considered.? Why
stop at VHF though?? Why
not VHF, UHF, and even microwave with a BITX as the baseband system?
73's
Arv
_._
Do you Yahoo!?
|
Rahul VU3WJM
That is the beauty of the BITX design.? It has so much potential that it gets one to thinking about all the interesting possibilities.?
Here are some more "ideas" that relate to the BITX design:
? (1) Since the BFO is a 10 MHz crystal oscillator, one might be able to divide that oscillator down to become the reference clock for a digital dial (frequency counter).? It seems this would require that it be right on 10.000,000 MHz, so this would require that the ladder filter pass band be positioned properly relative to the BFO frequency.? Or...maybe the accuracy of the 10.000,000 MHz is not that critical.? Someone needs to do the math to see how far "off frequency" the counter reference oscillator can be and still provide reliable 100 Hz resolution for a digital dial.? Remember that for an accurate 100 HZ counter the reference oscillator will probably be divided down to 50 Hz to drive the count gate circuit.
? (2) What about building multiple "front-ends" on different bands for the BITX, but re-using the IF, BFO/detector and audio sections.? This could provide a low-cost way to obtain multiple band coverage.? Something like tunable transverters for the front end, interfacing with a 10 MHZ fixed frequency back end module is what comes to mind.
? (3)? As Rahul suggested, the IF does not have to be on 10.0 MHz.? However, deviating from the original design will require that you pay particular attention to harmonics and resultant image frequencies to avoid unwanted signals in the passband.? I have been considering an LF version of the BITX on 160-190 KHz ( the US unlicensed experimenter band ).? Whatever might be done there should be applicable to areas of the world where you are allowed amateur operations on 76 KHz or 136 KHz.? Alas, our Federal Communications Commission (FCC) in the US does not yet allow licensed amateur radio operation on any LF band so we are stuck with the 1 Watt and 50-foot maximum radiator restrictions of our unlicensed LF band.
?????? Developing an LF version of the BITX (BITX-LF...?) provides a temptation to modify the basic design by customizing it for the lower frequencies, but I think that finding a set of VFO, BFO, & IF frequencies that will let one adhere closely to the original design, except for the frequency coverage, is more interesting.?
? (4)? Rahul's thoughts on using the BITX-xx as a front-end for SDR (Software Defined Radio) is an easy way to enter this fascinating aspect of our hobby.? All that is required for single-band operation is to couple the RX audio from the top of your Volume control to the sound card input on your computer ( so you can adjust the speaker volume without disturbing the sound card audio level ), and to bring the audio output from your computer sound card through a suitable attenuator and into the microphone input of the BITX.? Then with any of the appropriate FREEWARE or SHAREWARE programs that are available via the Internet, you can be on the air with computerized CW, PSK-31, MSK-xxx, RTTY, and so on.? This would be a manually-tuned version of SDR, but if you add a DDS VFO to your BITX, then the frequency can also be controlled via computer.?? Most of the available programs provide PTT (Push To Talk) keying via the DTR lead on your serial port, but it should also be possible to incorporate a simple VOX circuit that keys the transmit function whenever the computer begins sending any type of tone from the sound card.? This way you will not be tying up your serial port just to key the transceiver.
Maybe we will have to start an "IDEAS" public file on the BITX20 forum as well as one for? MODIFICATIONS.? People could "check out" an IDEA and develop it until it becomes a MODIFICATION.
Keep thinking!? It is fun, and it may help keep your brain alive and active well into old age.
Arv
_._
On Sun, 2004-07-18 at 12:20, Rahul Srivastava wrote:
Hi!
?
Arv,
?
Baseband......
?
This is good thinking. I was wondering on a 2.5Mhz If for BITX and 10Mhz xtal clock for detection and rest thru SDR soft. Only a couple of more diodes to add (I Q Mixer), another balun for phase splitter, 74HC74 for osc signals.
Good thought re. using the 10 MHZ for quad-phase detector and also dividing it down to a lower IF frequency for the BFO function.? Let us all know how it works.
I wonder if anybody is thinking about a SSB phasing-mode version of the BITX with phase-synchronous detection of SSB signals ( Rahul's idea )?? That might let us get by with a minimal IF filter ( just enough filtering to avoid desensitization by other strong in-band signals and to avoid out-of-band image reception ).
?
Should not be a problem on lower bands even with a? L/C VFO for conversion.
?
This?place really got the grey matter working.
?
73
?
Rahul VU3WJM
?
?
?
Arvid Evans wrote:
Hans
I think that either yourself or Farhan will have to build any "group
writable directory", if it is even supported by Yahoo.? In building my
K7HKL directories in the Files and Photos sections I do not recall
seeing any option where a non-administrator for the group could make
those directories group writable.
If you do provide group writable subdirectories for specific subject
content it may be necessary to set up some guidelines to help? define
just what is expected and/or acceptable in these special directories
That sounds like a possible administrative nightmare!? I'm now
wondering if it was such a good idea?? ;-/
Hey!? The person who contemplated using a BITX20 to drive a VHF
transverter is really thinking.? That opens up a whole new set of
modifications that I had not considered.? Why stop at VHF though?? Why
not VHF, UHF, and even microwave with a BITX as the baseband system?
73's
Arv
_._
Do you Yahoo!?
|
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?
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Arv I think that either yourself or Farhan will have
to build any "group writable directory", if it
is even supported by Yahoo. In building my
K7HKL directories in the Files and Photos
sections I do not recall seeing any option
where a non-administrator for the group could
make those directories group writable. I just had a quick look at this. With the current group settings, any member can create directories and any member can create files in any directory. What you cannot do is edit or delete an existing file unless you are the one who created it. Moderators can edit and delete all files. There does not seem to be any way for non-moderators to have write access to files which they did not create. So we can do this no problem, as long as people don't all want to edit each other's documents. In practice I don't think this restriction should be too troublesome. If you do provide group writable subdirectories
for specific subject content it may be necessary
to set up some guidelines... I am in favour of as few rules and guidelines as possible. Just let the creativity flow freely and let's waste as little time on administration as possible. If later, it appears that the volume of ideas or modifications has become large and the folders are disorganised and confusing, then we can formulate some guidelines at that point if necessary. That's my own view though, if people would like it more rigid then I'm not that fussed either way. 73 Hans G0UPL
|
Hi!
?
The more I think more I am convinced that this is indeed a simple way experiment with modern techniques.
?
If we plan to go SDR route along with downconversion then we find the critical Xtal filter eliminated . We already have a 10Mhz BFO so one stage less.?74HC74 is a common enough device.
Now for the quad. detect?we arrive at 2.5Mhz IF.?A simple?bandpass here would suffice say another couple of tap washers or modifed? 455Khz retuned If transformer. The LO can be couple of surplus 16meg xtals. With a view of abt 32Khz spectrum on the display we also eliminate much of readout and slow motion tuning.
We already have a mixer?as PD / Bal mod?we now just add 4 more diodes and make another mixer to get the I Q signals. I feel we can omit the diplexer and provide active decoupled?bipolar preamps as in KK7B designs. ( Not planning for the ultimate IMD figures)
Now for the best part the whole design is BI directional and the SDR1000 software generates I Q signals in transmit mode. Not much else needs to be done for a complete SDR Transciever.?
?
Experimentation still the? game. Maybe one day BITX would be a fully SDR.
?
73
?
Rahul VU3WJM??
?
Arv Evans wrote:
Rahul VU3WJM
That is the beauty of the BITX design.? It has so much potential that it gets one to thinking about all the interesting possibilities.?
Here are some more "ideas" that relate to the BITX design:
? (1) Since the BFO is a 10 MHz crystal oscillator, one might be able to divide that oscillator down to become the reference clock for a digital dial (frequency counter).? It seems this would require that it be right on 10.000,000 MHz, so this would require that the ladder filter pass band be positioned properly relative to the BFO frequency.? Or...maybe the accuracy of the 10.000,000 MHz is not that critical.? Someone needs to do the math to see how far "off frequency" the counter reference oscillator can be and still provide reliable 100 Hz resolution for a digital dial.? Remember that for an accurate 100 HZ counter the reference oscillator will probably be divided down to 50 Hz
to drive the count gate circuit.
? (2) What about building multiple "front-ends" on different bands for the BITX, but re-using the IF, BFO/detector and audio sections.? This could provide a low-cost way to obtain multiple band coverage.? Something like tunable transverters for the front end, interfacing with a 10 MHZ fixed frequency back end module is what comes to mind.
? (3)? As Rahul suggested, the IF does not have to be on 10.0 MHz.? However, deviating from the original design will require that you pay particular attention to harmonics and resultant image frequencies to avoid unwanted signals in the passband.? I have been considering an LF version of the BITX on 160-190 KHz ( the US unlicensed experimenter band ).? Whatever might be done there should be applicable to areas of the world where you are allowed amateur operations on 76 KHz or 136 KHz.? Alas, our Federal Communications Commission (FCC) in the US does not yet
allow licensed amateur radio operation on any LF band so we are stuck with the 1 Watt and 50-foot maximum radiator restrictions of our unlicensed LF band.
?????? Developing an LF version of the BITX (BITX-LF...?) provides a temptation to modify the basic design by customizing it for the lower frequencies, but I think that finding a set of VFO, BFO, & IF frequencies that will let one adhere closely to the original design, except for the frequency coverage, is more interesting.?
? (4)? Rahul's thoughts on using the BITX-xx as a front-end for SDR (Software Defined Radio) is an easy way to enter this fascinating aspect of our hobby.? All that is required for single-band operation is to couple the RX audio from the top of your Volume control to the sound card input on your computer ( so you can adjust the speaker volume without disturbing the sound card audio level ), and to bring the audio output from your computer sound
card through a suitable attenuator and into the microphone input of the BITX.? Then with any of the appropriate FREEWARE or SHAREWARE programs that are available via the Internet, you can be on the air with computerized CW, PSK-31, MSK-xxx, RTTY, and so on.? This would be a manually-tuned version of SDR, but if you add a DDS VFO to your BITX, then the frequency can also be controlled via computer.?? Most of the available programs provide PTT (Push To Talk) keying via the DTR lead on your serial port, but it should also be possible to incorporate a simple VOX circuit that keys the transmit function whenever the computer begins sending any type of tone from the sound card.? This way you will not be tying up your serial port just to key the transceiver.
Maybe we will have to start an "IDEAS" public file on the BITX20 forum as well as one for? MODIFICATIONS.? People could "check out" an IDEA and develop it until it becomes a
MODIFICATION.
Keep thinking!? It is fun, and it may help keep your brain alive and active well into old age.
Arv
_._
On Sun, 2004-07-18 at 12:20, Rahul Srivastava wrote:
Hi!
?
Arv,
?
Baseband......
?
This is good thinking. I was wondering on a 2.5Mhz If for BITX and 10Mhz xtal clock for detection and rest thru SDR soft. Only a couple of more diodes to add (I Q Mixer), another balun for phase splitter, 74HC74 for osc signals.
Good thought re. using the 10 MHZ for quad-phase detector and also dividing it down to a lower IF frequency for the BFO function.? Let us all know how it works.
I wonder if anybody is thinking about a SSB phasing-mode version of the BITX with phase-synchronous detection of SSB signals ( Rahul's idea )?? That might let us get by with a minimal IF filter ( just enough filtering to avoid desensitization by other strong in-band signals and to avoid out-of-band image reception ).
Should not be a problem on lower bands even with a? L/C VFO for conversion.
?
This?place really got the grey matter working.
?
73
?
Rahul VU3WJM
?
?
?
Arvid Evans wrote:
Hans
Do you Yahoo!?
- 50x more storage than other providers!
|
