Date   
schematics

Chris Lindemann <kd5iku@...>
 

I have been using the schematics off of the bitx website, but it does
not seem to match up with the componets list in the files section
here. Is there a newer schematic? Is the parts list out of date?

Re: strange beat reception

Rahul Srivastava
 

Hi!!
I have tested and found few beats namely around 14.220 if I remember correctly in 20mtr version. Presently not on air due to heavy QRM at MQTH. ( Just back from month long summer vacation)
Mixing products are also result of nice round number BFO and VFO freq used. Changing the IF to something like 8.8667Mhz ie 2X EU colour burst might be a better option. Sometime back I made one Rx based on TA7358AP FM radio frontend chip.all stages active and inbuilt mixer doubly balanced IF still was 10mhz surprisingly I didnt get the beat , probably it may have something to do with harmonic related and non linaer nature of diode mixer.

73
Rahul VU3WJM


eugen <eugen_55ee@...> wrote:
Hi!
Thanks for you replyes.
Lately I dind'thave much time to try changes you proposed, but last
week I tryed usind a double balanced mixer in the front-end, with no
change.I still receive those beat signals. The receiver works fine, I
receive many stations, but there are some beat signals very powerfull.
I measured the BFO frequency, it is 9.9967MHz. The frecuency of the
VFO where I receive the most powerfull beat is 4.284MHz, so the beat
occurs between 3*9.9967=29.9901MHz and 7*4.284=29.988MHz.There are
also other beats.
Then I tryed to put the mixer in a small PCB shieded box with pins
for IN, OUT, VFO, with no changes in reception.
I discovered shielding is not such a great problem,because the VFO
is in a shielded box, and the VFO signal is aplied to the DBM with a
shielded cable. When I disconnect the cable from the DBM I receive
the beats only if I put the cable very close to the product detector
the efect of the shielding is not so important. The VFO signal
travels through the IF chain.
So, I suspect the transformers used in the double balanced mixer are
not perfectly balanced so a small part of the VFO signal is aplied to
the IF amp. Maybe the IF amp is driven in saturation, producing many
harmonics or/and the attenuation of the XTAL ladder is to small and
the signal passes to the product detector.
I wind the transformers with trifilar twisted wire, on a TOKO IF
core.
Ok, so if you had patience to read all I want to ask you about a
solution. The receiver works so great, but there are those beats... I
wish it will work correct in all the band
Thanks for you sugestions!

--- In BITX20@..., "Ashhar Farhan" <farhan@...> wrote:

Try a double balanced mixer in the front-end
- farhan

-----Original Message-----
From: BITX20@... [mailto:BITX20@...] On
Behalf
Of Rahul Srivastava
Sent: Sunday, June 04, 2006 11:32 PM
To: BITX20@...
Subject: Re: [BITX20] Re: strange beat reception


Hi!
Sheilding is indeed key to the problem. When I do a TRX I normaly
place BFO & VFO as far as possible. This is quite evident from my
PCB
layout where you find them on diagonaly opposite cprners.
BITX uses diode mixers that in turn require higher injection
level.
This makes shielding very critical for spurious free operation.
Despite
all precaution you may still hear some very faint beats.
73
Rahul VU3WJM

Allison Parent <kb1gmx@...> wrote:
I must assume your doing 20m bitx using 10.00mhz IF.

The 6th harmonic of the VFO is 24mhz -10 mhz IF equals 14mhz and
likely
there are other harmonic beats.

Optimally the VFO above the IF is less prone to this but a 24mhz
VFO is
hard to make stable.

Solutions are hard to be sure of. Shielding each section
such as the VFO and buffer stage in a seperate box with
shielded cable connecting it to the mixer can help.

If you using the tap washers rather than toroid ferrite
you will have more unwanted coupling at transformers and coils.
Again
orienting them differently or adding shielding between them may
help.


Allison


--- In BITX20@..., "eugen" <eugen_55ee@> wrote:

I built the small signal part of the BITX - no PA and driver
stage -
and tested the receiver. I used a different type of VFO I had,
that
tunes 4.150-4.300MHz (I plan to use a FLL or DDS in the future to
cover the entire band).

The receiver works fine in almost all band, but there are 2
frequencyes where I receive a kind of beat signal, very powerfull
(the audio signal frequency changes like when I tune in to an
unmodulated station).

First I suspected that the 14MHz band pass filter has to small
attenuation of the image frequency, because I used only 2 paralel
circuits instead of 3, and the image signal can be in the
broadcast
band, with high power transmitters. So I shorted the receiver
input
with a wire. But I received the same beat signals.

So I need your help to determine the cause of these beat signals.
Can
this be an interference of the VFO with the BFO, or some harmonic
combination? The VFO is an ECO followed by a buffer.

Thanks for your help.








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Re: strange beat reception

Eugen, Eugen Phelps, Phelps
 

Hi!
Thanks for you replyes.
Lately I dind'thave much time to try changes you proposed, but last
week I tryed usind a double balanced mixer in the front-end, with no
change.I still receive those beat signals. The receiver works fine, I
receive many stations, but there are some beat signals very powerfull.
I measured the BFO frequency, it is 9.9967MHz. The frecuency of the
VFO where I receive the most powerfull beat is 4.284MHz, so the beat
occurs between 3*9.9967=29.9901MHz and 7*4.284=29.988MHz.There are
also other beats.
Then I tryed to put the mixer in a small PCB shieded box with pins
for IN, OUT, VFO, with no changes in reception.
I discovered shielding is not such a great problem,because the VFO
is in a shielded box, and the VFO signal is aplied to the DBM with a
shielded cable. When I disconnect the cable from the DBM I receive
the beats only if I put the cable very close to the product detector
the efect of the shielding is not so important. The VFO signal
travels through the IF chain.
So, I suspect the transformers used in the double balanced mixer are
not perfectly balanced so a small part of the VFO signal is aplied to
the IF amp. Maybe the IF amp is driven in saturation, producing many
harmonics or/and the attenuation of the XTAL ladder is to small and
the signal passes to the product detector.
I wind the transformers with trifilar twisted wire, on a TOKO IF
core.
Ok, so if you had patience to read all I want to ask you about a
solution. The receiver works so great, but there are those beats... I
wish it will work correct in all the band
Thanks for you sugestions!

--- In BITX20@..., "Ashhar Farhan" <farhan@...> wrote:

Try a double balanced mixer in the front-end
- farhan

-----Original Message-----
From: BITX20@... [mailto:BITX20@...] On
Behalf
Of Rahul Srivastava
Sent: Sunday, June 04, 2006 11:32 PM
To: BITX20@...
Subject: Re: [BITX20] Re: strange beat reception


Hi!
Sheilding is indeed key to the problem. When I do a TRX I normaly
place BFO & VFO as far as possible. This is quite evident from my
PCB
layout where you find them on diagonaly opposite cprners.
BITX uses diode mixers that in turn require higher injection
level.
This makes shielding very critical for spurious free operation.
Despite
all precaution you may still hear some very faint beats.
73
Rahul VU3WJM

Allison Parent <kb1gmx@...> wrote:
I must assume your doing 20m bitx using 10.00mhz IF.

The 6th harmonic of the VFO is 24mhz -10 mhz IF equals 14mhz and
likely
there are other harmonic beats.

Optimally the VFO above the IF is less prone to this but a 24mhz
VFO is
hard to make stable.

Solutions are hard to be sure of. Shielding each section
such as the VFO and buffer stage in a seperate box with
shielded cable connecting it to the mixer can help.

If you using the tap washers rather than toroid ferrite
you will have more unwanted coupling at transformers and coils.
Again
orienting them differently or adding shielding between them may
help.


Allison


--- In BITX20@..., "eugen" <eugen_55ee@> wrote:

I built the small signal part of the BITX - no PA and driver
stage -
and tested the receiver. I used a different type of VFO I had,
that
tunes 4.150-4.300MHz (I plan to use a FLL or DDS in the future to
cover the entire band).

The receiver works fine in almost all band, but there are 2
frequencyes where I receive a kind of beat signal, very powerfull
(the audio signal frequency changes like when I tune in to an
unmodulated station).

First I suspected that the 14MHz band pass filter has to small
attenuation of the image frequency, because I used only 2 paralel
circuits instead of 3, and the image signal can be in the
broadcast
band, with high power transmitters. So I shorted the receiver
input
with a wire. But I received the same beat signals.

So I need your help to determine the cause of these beat signals.
Can
this be an interference of the VFO with the BFO, or some harmonic
combination? The VFO is an ECO followed by a buffer.

Thanks for your help.








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Re: T1 winding

Chris Lindemann <kd5iku@...>
 

That is exactly what I was needing to know. I had never ran into the
whole bifilar and trifilar before. Thanks for the info!

Re: T1 winding

Arv Evans
 

Chris

The transformers you are talking about are what is known as
"transmission line transformers" where the wires making up the windings
are twisted together. This causes all the windings to have exactly the
same characteristics (impedance, resistance, distributed capacitance,
etc.) and makes their use in HF circuits much more predictable. Bifilar
coils would be two windings, made up from a pair of insulated wires that
are twisted together. Trifilar would be three windings made up of three
wires twisted together. Quadrifilar would be 4 wires, and so on.

You can find information on multi-filar coils at:

http://en.wikipedia.org/wiki/Bifilar_coil

Making bifilar, trifilar, quadrifiler, etc. coils is easier if each wire
is a different color. This helps to separate then when you are finished
winding, but same-color wire can be used and an ohmmeter applied to
identify the ends of each winding. Usual convention is to twist the
wires at between 7 and 12 twists per inch. Each construction article
will probably suggest a twist rate for it's particular multi-filar coils.

In the BITX20 forum section for photos you will find a directory for
K7HKL and in that directory a picture file called "Trifilar Twister Tool
<http://ph.groups.yahoo.com/group/BITX20/photos/view/7528?b=6>". This
picture shows how to build a simple tool for twisting the wires that
will be used to make trifilar windings.

I have just now added a new picture at "photos/K7HKL/Trifilar Coil"
which shows a typical trifilar wound coil with the ends separated into
the three separate windings.

So, use insulated wire, twist three sections together, wind this 3-wire
section on your form for the required number of turns, separate the
ends, and identify which wires make up each winding. That is all there
is to it.

Hope this helps.

Arv K7HKL
_._


Chris Lindemann wrote:


Quick question. I am a novice when it comes to winding transformers. I
am trying to understand exactly how the t1 transformer is wound. I
understand it is trifilar, but I do not understand the whole part
about making the thrid one a secondary. It sounds like all three are
supposed to be twisted together. Are they? Pardon my ignorance. The
learning curve is steep. I have never ran into a transformer like this
on any of my qrp projects over the years.

T1 winding

Chris Lindemann <kd5iku@...>
 

Quick question. I am a novice when it comes to winding transformers. I
am trying to understand exactly how the t1 transformer is wound. I
understand it is trifilar, but I do not understand the whole part
about making the thrid one a secondary. It sounds like all three are
supposed to be twisted together. Are they? Pardon my ignorance. The
learning curve is steep. I have never ran into a transformer like this
on any of my qrp projects over the years.

Re: New file uploaded to BITX20

Ruud Jongeling <pe2bs@...>
 

Thanks. Mistake in the schema. New upload is on it's way.

73
Ruud.

--- In BITX20@..., "ve7hcw" <cw_keyer@...> wrote:

Hello
I noticed that your schematic has an extra connection between
R45
and R46 10K resistors shorting out two sections of the phase shift
audio oscillator network.
wayne ve7hcw




--- In BITX20@..., BITX20@... wrote:


Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the BITX20
group.

File : /PE2BS/BITX8020/lf.BMP
Uploaded by : pe2bs <pe2bs@>
Description : LF-module

You can access this file at the URL:
http://groups.yahoo.com/group/BITX20/files/PE2BS/BITX8020/lf.BMP

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

pe2bs <pe2bs@>

Re: New file uploaded to BITX20

ve7hcw <cw_keyer@...>
 

Hello
I noticed that your schematic has an extra connection between R45
and R46 10K resistors shorting out two sections of the phase shift
audio oscillator network.
wayne ve7hcw

--- In BITX20@..., BITX20@... wrote:


Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the BITX20
group.

File : /PE2BS/BITX8020/lf.BMP
Uploaded by : pe2bs <pe2bs@...>
Description : LF-module

You can access this file at the URL:
http://groups.yahoo.com/group/BITX20/files/PE2BS/BITX8020/lf.BMP

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

pe2bs <pe2bs@...>

New file uploaded to BITX20

BITX20@...
 

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the BITX20
group.

File : /PE2BS/BITX8020/lf.BMP
Uploaded by : pe2bs <pe2bs@...>
Description : LF-module

You can access this file at the URL:
http://groups.yahoo.com/group/BITX20/files/PE2BS/BITX8020/lf.BMP

To learn more about file sharing for your group, please visit:
http://help.yahoo.com/help/us/groups/files

Regards,

pe2bs <pe2bs@...>

RF Amp Add-In

k5oor <vstamps@...>
 

Hello, if you are interested in adding-in a higher power RF amplifier,
you are invited to visit http://www.hfprojects.com for several home
construction projects. The individual boards and parts are available
for DIY use.
73 K5OOR - Virgil hfprojects.com

Re: BFO

bambazonke01 <jimandruth@...>
 

Sometimes it helps to reduce the drive from the BFO and LO . It is
surprising how signals seem to mix and get around in a home made rig.
I tried a 9 mhz IF and a 5 to 5.5 Mhz VFO to give 80 and 20 M
operation with a multiband preselector. It was amazing how many
heterodynes squeals and burps I got out of that simple piece of
equipment. There were more signals than a barrel full of monkeys
---all trying to get out.
I eventually shielded the heck out of everything with a screw on cover
and reduced oscillator levels and everything quietened down. I think
oscillator levels were too high and were causing some of the switching
diodes to conduct and multiply frequency.
Jim VE3DDY

Re: BFO

Ruud Jongeling <pe2bs@...>
 

Hello Paul,

I agree with Jim that it is unlikely that your BFO is breaking in
the IF and later stages. When I "coupled" the BFO signal with a wire
above the IF and LF sections in my own BITX I noticed an increase of
noise and (with further coupling on the IF section) a decrease of lf
signal. The high pitched tone also suggests a difference in frequency
with the BFO of a few Kc.

Some instability in one of the stages or between stages could be a
possibility but where? When I have such a problem (and I have had
many!) I start with the last module (LF) and connect the other
modules one by one (BFO+demodulator, IF2, IF-Filter, IF1, mixer, RF)
until I can locate the instability.

I built each module on a PCB with shielding between them about 2,5 cm
high. To avoid instability caused by DC each module (stage) has it's
own decoupling with capacitors and chokes.

73

Ruud
PE2BS




--- In BITX20@..., m0eme432@... wrote:

Hi all, Ive noticed a very high pitched tone coming out of the
speaker, it
seems louder when its not tuned into a signal as such. Could this
be the
BFO breaking into the IF and later stages???
I havent built it into a box yet but its all mounted on a common
PCB and
with screens around each stage about 1" high. I used coax and power
leads
as short as posible. Any ideas??? because its spoiling the
enjoyment.
Thanks Paul M0EME

___________________________________________________________

Tiscali Broadband from 14.99 with free setup!
http://www.tiscali.co.uk/products/broadband/

Re: BFO

bambazonke01 <jimandruth@...>
 

--- In BITX20@..., m0eme432@... wrote:

Hi all, Ive noticed a very high pitched tone coming out of the
speaker, it
seems louder when its not tuned into a signal as such. Could this be the
BFO breaking into the IF and later stages???
I havent built it into a box yet but its all mounted on a common PCB and
with screens around each stage about 1" high. I used coax and power
leads
as short as posible. Any ideas??? because its spoiling the enjoyment.
Thanks Paul M0EME
Paul,
Unlikely. The BFO works at a freq away above your hearing. BFO noise
sounds more like a hash noise or continuous static.
You probably have some slight feedback in an audio circuit. Try using
a .01 or a .005 capacitor and connect one end to ground and probe
around with the other end. You won't do any damage that way . With the
radio running and listening to the audio you will hear when the noise
stops.
Jim VE3DDY

BFO

m0eme432@...
 

Hi all, Ive noticed a very high pitched tone coming out of the speaker, it
seems louder when its not tuned into a signal as such. Could this be the
BFO breaking into the IF and later stages???
I havent built it into a box yet but its all mounted on a common PCB and
with screens around each stage about 1" high. I used coax and power leads
as short as posible. Any ideas??? because its spoiling the enjoyment.
Thanks Paul M0EME

___________________________________________________________

Tiscali Broadband from 14.99 with free setup!
http://www.tiscali.co.uk/products/broadband/

Re: Your Simple SSB Tranceiver

Ashhar Farhan <farhan@...>
 

Dear John,

Thanks for the kind words. I no longer claim being the 'author' of BITX.
I only did the initial design. Now, a whole community of really nice
hams are building and exploring the BITX. We are now an active yahoo
group. I urge you to join us at http://groups.yahoo/com/groups/BITX20
and share your experience and knowledge.


About your specific questions:

1) the attenuator - I put it in to provide the second mixer with a
resistive termination at two ports (the IF amplifier and the audio
ports). It also provides a DC return that would have otherwise required
an RF choke (I had none).

2) The balancing trimmers on two sides of the modulator may or may not
be required depending upon the balance in the rest of the circuitry. For
instance, if you took care to have a neatly made bifiliar transformer,
The differences in stray capacitances in the parallel windings wont
really be much and they will cancel each other out. I was shooting for a
design that is easily reproducible. Hence, I left the capacitors in. I
suspect that these will be required at 10MHz where the reactive balance
because more dominant.

3) You are entirely correct about the output levels of the BFO changing
between the USB and the LSB. This is an issue with VXOs that their
output amplitude will vary across the range. Hence, it might be a good
idea to drive the output through a clipper. I think, biasing on the Q6
(the emitter follower from the BFO) should be tweaked to produce a
clipped output. Some might think that this could lead to harmonic mixing
at the second mixer - the crystal filter in the signal path will filter
out those harmonic responses.


4) AGC would be a welcome addition. A number of people have added
various AGC elements to the basic design. My worry is that applying AGC
to IF stage would mean that we will need to separate out the IF paths
after the crystal filter, thereby upsetting the bidirectional nature of
the design (which leads to the simplicity of the original design). I
have been thinking about an audio derived AGC that can also control the
gain of an audio pre-amplifier.


There are three things I wish I had done differently in the original:

1) The VFO is a bit noisey. An FET based VFO gives a far quiter
receiver. I guess it is equally possible to make a less noisey VFO from
bipolars. It is a question of correctly choosing the biasing current in
the transistor (or maybe trying out the vacker configuration).

2) the first mixer should have expended another trifilar transformer and
two diodes and used a doubly balanced mixer.

3) the audio preamplifier is not matched to the detector. Instead, a
common base audio preamp biased for 0.5ma current with an emitter
follower (as often used by W7ZOI and W7EL in their designs) would have
made for a better receiver. Probably, we could also add gain control to
this design by robbing current from the audio pre-amp.

- farhan

-----Original Message-----
From: Johan Forrer [mailto:jbforrer@...]
Sent: Sunday, June 25, 2006 3:11 AM
To: farhan@...
Subject: Your Simple SSB Tranceiver


Dear Farhan,

Thought I'd write to you regarding your simple SSB
transceiver design I found on the net.

First, thank you for sharing this neat project.
Personally have learned a great deal from it, just
doing it myself and seeing things come together.

For my project, used a set of crystals for a 9 MHz IF
that I ordered off the web from INRAD (qth.com/INRAD).
They have a 2.4 kHz version and a 600 Hz version for
CW. Think that performs much like you described in
your article; audio sounds really nice and crisp. The
receiver is quite hot (sensitive) and a pleasure to
listen to.

A few questions:

1) The -4dB pad. Should that not have been placed
after the last IF amplifier stage, prior to the mixer,
instead of after the mixer? Have read the discussion
about the purpose of that attenuator in EMRF, however,
do miss that little extra gain and resultant
performance in the receiver with the attenuator
installed. The receiver just sounds better, so left
the attenuator out.

2) Added the two phasing capacitors to the second
mixer like you had done for the BITX. From my
observations, that appears to make a significant
difference in carrier null. Doing the same at the DSB
modulator is not as dramatic. Should it?

3) It appears the output level of the BFO differs
substantially between USB and LSB. As it is, I already substituted with
Schottkey diodes in the mixers. It does fine on USB, OK on LSB, but
think it would help if the BFO level can be increased.

Now for the wish list ...

4) Audio-derived AGC would be a welcome addition. Find
that one has to reach for the volume control when a
strong signal just about kills your ears. Any ideas
here that does not degrade the front-end mixer?
Perhaps IF AGC?

Thanks, 73,

Johan, KC7WW.

Re: {Spam?} {Disarmed} has anyone built a 10M version yet

Ashhar Farhan <farhan@...>
 

Paul,

You 28 mhz version might actually be much simpler to implement. You can
use regular 18mhz crystals for IF and this will require 10mhz vfo. With
a 10mhz vfo, you can expect fairly decent stability as well as the
ability to entirely tune it with a varactor.

- farhan

-----Original Message-----
From: BITX20@... [mailto:BITX20@...] On Behalf
Of m0eme432
Sent: Thursday, June 22, 2006 5:16 PM
To: BITX20@...
Subject: {Spam?} {Disarmed} [BITX20] has anyone built a 10M version yet



Ive just got my bitx20 version 3 going and Im well happy with the
performance. I was wondering has anyone tried a 28mhz version?? If
anyone has what frequencies did you use for the VFO, BFO, IF and xtal
filters???
Thanks Paul M0EME

has anyone built a 10M version yet

m0eme432 <laurenloz@...>
 

Ive just got my bitx20 version 3 going and Im well happy with the
performance. I was wondering has anyone tried a 28mhz version?? If
anyone has what frequencies did you use for the VFO, BFO, IF and xtal
filters???
Thanks Paul M0EME

Re: New to this forum. Where to start?

John & Lorna <johnlorna@...>
 

Steve,
Thank you for the reply.
I have ordered my circuit boards from Far Circuits and have noted some
problems with their first batch some years ago. I found this searching
through the old messages. Hope they have corrected the errors but I'll
be looking for them nonetheless.

I would be interested in seeing or having a copy of the art work for your
BITX project. I could have Far Circuits make up the boards and compare
them with the ones I'll soon be getting. I also agree with you on the Altoids
tin! At least one of my BITX will be built in an old Bud box with black
wrinkle finish, about 6.5"H x 7.25"D x 11"W. The box is large enough
to contain the circuit boards and a couple 12v gell cell batteries. I plan
on using 1930's vintage dials and knobs to complete the illusion.

I also have a more modern case that is a bit smaller, it would go well with
a digital readout.

Thanks for the advice,
John KB7NRN

At 04:38 PM 6/16/2006 +0100, you wrote:
Hi John

Not everyone is on line 24/7, help sometimes takes its time to filter
through, but rest assured there is plenty of it around.

For a different view, we have been using the bITX as our project at our
radio classes over here in Bath and I have Farhan's agreement to include
the instructions in an RSGB book which is now planned for Christmas release.
I laid out the circuits on 3 PCBs giving our newcomers plenty of room to
work. The end result is a bit bigger, but who wants a 20m SSB rig in an
Altoids tin? Sorry miniture fans. We have a few completed and on air a
number of others in progress.

Advice?
Take your time. One stage at a time.
Don't expect Black Box standard - lack of AGC is most common criticism.
Do expect things not to work first time and be pleasantly surprised when
they do!
Don't get too hung up on components - I used very cheap Russian
transistors in place of BC547s and they work well.
As Arv has said, if you have specific questions you will get plenty of
answers.

Good luck with your project.

73, Steve, G0FUW

Re: {Spam?} {Disarmed} BITX80

Steve Hartley G0FUW <g0fuw@...>
 

Folks
I have built 4.433MHz SSB filter to VK3XU TCF40 design - VFO is around 11MHz Hartley circuit - filter uses 4 crystals with 33pF caps, series in and out, and to deck between each crystal. Crystals were removed from old TV PCBs.
His almost identical TCF80 project uses VFO on 9.5-9.9MHz and 6MHz crystals, I guess for potential sproggie reasons outlined earlier.
I believe Drew's book 'Radio Projects for the Radio Amateur' is now published by MFJ but I have not seen a copy to be sure. It used to be available through G-QRP Club. Good value if you can find a copy!
73, Steve, G0FUW

----- Original Message -----
From: Ashhar Farhan
To: BITX20@...
Sent: Saturday, June 17, 2006 7:26 AM
Subject: RE: {Spam?} {Disarmed} [BITX20] BITX80


dear van helsing,

i wouldn't go with such low frequency crystals. the reason is that the
crystal bandwidht is a percentage of the actual crystal frequency.
hence, at 10mhz it is easy to realize an ssb filter. at 4.333mhz, a cw
filter is more realizable.

if you did design (in theory at least) for a 4.33mhz filter, it would
have a bad skirt (band rejection) and group delays. It will appear
'ringing' and muffled. there is a way around it though:

1. create a small circuit to measure the crystal parameters.
2. do a theoretical design with buttersworth response. the design will
appear like the existing ladder filter with inductors in parallel with
the crystals. you will have to dig into the design theory. i would
recommend wes hayward's 'Introduction to RF Design' or the ARRL's
'Experimental Method's in RF Design'.

Ok, all that said ... go ahead and play around. try different capacitors
around it. there is a small program in the group folder that measure the
crystal response easily in conjuction with a PC. if you have time, you
can experiment with it. You will, in all probability have a good design.

At the design time, i did toy with the idea of a 3.57MHz IF. it would
have been so easy to do a 10mhz vco and just flip the RF filters between
7MHz and 14MHz bands. I let it go because didn't have the competency to
do a reproducible ssb filter at lower frequencies. I would love to have
someone do that. maybe it is you.

- farhan

-----Original Message-----
From: BITX20@... [mailto:BITX20@...] On Behalf
Of van helsing
Sent: Friday, June 16, 2006 3:09 PM
To: BITX20@...
Subject: {Spam?} {Disarmed} [BITX20] BITX80

Dear all hams here,

i wanna mods BITX20 to BITX80 and change x'tal with 4.43 mhz coz its
very easily to find in my town. i need help to build BPF, VFO/VXO and
maybe other variable must be change. thanks for your help.

__________________________________________________
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Tired of spam? Yahoo! Mail has the best spam protection around
http://mail. <http://mail.yahoo.com> yahoo.com

Re: {Spam?} {Disarmed} BITX80

Ashhar Farhan <farhan@...>
 

dear van helsing,

i wouldn't go with such low frequency crystals. the reason is that the
crystal bandwidht is a percentage of the actual crystal frequency.
hence, at 10mhz it is easy to realize an ssb filter. at 4.333mhz, a cw
filter is more realizable.

if you did design (in theory at least) for a 4.33mhz filter, it would
have a bad skirt (band rejection) and group delays. It will appear
'ringing' and muffled. there is a way around it though:

1. create a small circuit to measure the crystal parameters.
2. do a theoretical design with buttersworth response. the design will
appear like the existing ladder filter with inductors in parallel with
the crystals. you will have to dig into the design theory. i would
recommend wes hayward's 'Introduction to RF Design' or the ARRL's
'Experimental Method's in RF Design'.

Ok, all that said ... go ahead and play around. try different capacitors
around it. there is a small program in the group folder that measure the
crystal response easily in conjuction with a PC. if you have time, you
can experiment with it. You will, in all probability have a good design.

At the design time, i did toy with the idea of a 3.57MHz IF. it would
have been so easy to do a 10mhz vco and just flip the RF filters between
7MHz and 14MHz bands. I let it go because didn't have the competency to
do a reproducible ssb filter at lower frequencies. I would love to have
someone do that. maybe it is you.

- farhan

-----Original Message-----
From: BITX20@... [mailto:BITX20@...] On Behalf
Of van helsing
Sent: Friday, June 16, 2006 3:09 PM
To: BITX20@...
Subject: {Spam?} {Disarmed} [BITX20] BITX80



Dear all hams here,

i wanna mods BITX20 to BITX80 and change x'tal with 4.43 mhz coz its
very easily to find in my town. i need help to build BPF, VFO/VXO and
maybe other variable must be change. thanks for your help.

__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail. <http://mail.yahoo.com> yahoo.com