Dear All,

I'm sorry I have confused the BITx20 with an earlier transceivers of Farhans which does use 2N3866.

I'll have to lay low for a while.

Dave M1DGS

Dear All

I looked at Farhans site and found

In that he says:-


Substitutions

The BF195 transistors can be substituted with any other HF transistor like 2N2222 etc. The 2N3866s are best not subsituted. The circuit works with slight increase in the noise figure if BF195 or equivalents are used in place of 2N3866s in the IF stages. The output power on the transmitter absolutely needs the 2N3866s. Subsituting them with other switching transistors didnt give good performance.

The IRF510 should not be subsituted with any other transistor. The other IRFs, though rated higher, have higher input capacitance which makes them a bad choice for 14MHz operation.

The LM380/LM386 can be subsituted with almost any other audio amplifier. Our first amplifier were Cambridge SoundWorks Sound System. If you turn down the bass, they are an excellent system for the shack. We have tried a TBA180, an LM386, an LM380 and even a glow-bug guitar amp. Feel free to experiment.



However thanks for the component supplier.

Dave M1DGS

Keytronics has 10MHz xtals at ?1.00 each (ten required)
and the 2N3866 seems to be obsolete. Do others see any
difficulties in sourcing parts.

I'm confused about the 2N3866 - what's it for? I see no mention on the
circuit diagram; the nice thing is that a variety of transistors will do in
this design.

Rapid Electronics () sell 10MHz crystals at
?0.38 each (?0.45 incl sales tax). That drops to ?0.305 (?0.36 incl VAT) for
QTY 25+. If enough people want them I'd be happy to order a batch and parcel
them out. People who are interested in 10, let me know within the next few
days and maybe we'll sort it out sometime next week. Assuming 25+, the price
would be ?3.86 for 10 including a 1st class UK postage stamp (overseas
postage stamp, extra).

Ok look, I'm not going into the kit business but while we're at it, if you
want them (also from Rapid):

25 BC547B's suitable for the rig: ?0.82 incl VAT
1 IRF510: ?1.53 incl VAT

Presumably the total weight will be under 60g so these will all fit under
the same single ?0.28 postage stamp.

So, for a LIMITED TIME ONLY... Crystals, transistors and the MOSFET, ?6.21
incl UK postage (overseas is fine, we just add the extra postage).

72/3 Hans G0UPL

What are members doing about component sources?

Keytronics has 10MHz xtals at ?1.00 each (ten required) and the
2N3866 seems to be obsolete. Do others see any difficulties in
sourcing parts.

Nevertheless it's a brilliant idea. Thanks Farhan

Dave M1DGS

What a good idea Hans to set up this group!

Much as I would like to be able to take credit Duncan, unfortunately it
wasn't my idea: I first heard it from Andrew VK3BFA on the
rec.radio.amateur.homebrew newsgroup, and think even he was referring to
Farhan thinking about it. My only part in it was to tell Farhan it's easy to
set up a mailing list on Yahoo, and offer to do the dirty work (all of 5
minutes!).

But welcome all (already we are 27 members) and introduce yourselves!

72/3 de Hans G0UPL

guys,

pete joins us on the group. he has details about substituting the tv
baluns cores with FT-37 cores. he has also pointed out that the receiver
gain is low. anybody else too who has experienced this problem?

i did encounter it on two sets that i assembled (out of three). in one set
it turned out o be a cold solder on an emitter bypass capacitor, in the
other case, it turned out that i had swapped the collecot load and the
base bias resistors on the audio pre-amp.

- farhan

---------- Forwarded message ----------
Date: Fri, 18 Jun 2004 08:14:12 +0530
From: Ashhar Farhan <computercorp@...>
To: jessystems@...
Cc: farhan@...
Subject: RE: BITX20 Transceiver

pete,

my hotmail box is choked. my other email address is farhan@....
and the mirror is on www.phonestack.com/farhan. i work at phonestack.

i will cross post this mail of yours back to the group. if you are getting
dx, then the receiver is probably sensitive enough. it is an unusually quite
receiver design. as a result, it does give the impression that it is not
sensitive enough. the acid test is to listen to the receiver without the
antenna and with the antenna attached. if the noise goes up substantially,
then it is sensitive enough.

- farhan

______________________________________
Ashhar Farhan
71, Huda Heights, MLA Colony,
Banjara Hills, Hyderabad.
INDIA 500034.
Phone - +91-40-23314077
______________________________________

From: "Pete Juliano" <jessystems@...>
To: "Ashhar Farhan" <computercorp@...>
Subject: BITX20 Transceiver
Date: Thu, 17 Jun 2004 12:08:13 -0700

Hi Ashhar,

Thank you for your trouble shooting hints. I will go through those.
Actually I have been copying signals from all over the world at the QTH
here near Seattle Washington. Last evening I heard IK2's, UA5's, LU7, KP2
and the usual mix of stateside stations. So it is not like it is deaf.

Thanks for the link to the user's group.

Oh. I tried sending you some photos of the rig but I guess hotmail does not
like jpg files. Is there some way to get some photos to you?

I don't know that there is a problem --but as compared to my other homebrew
gear it seems to be slightly less senstive. I am using a 2 element beam and
a fixed wire beam so it is not a case of a poor antenna. But I will follow
your trouble shooting hints. However as you say it is easy to get parts in
the wrong place and if you see my 2X6 inch board it is chock full --so it
would be easy to put the wrong part in the circuit. Must admit I have to
use a magnifying glass to read some of those really small parts.

I must open the audio full gain to get to the pain level in the headpohnes
--usually with the LM386 -1 it is about 1/2 gain so that is the basis of my
comments about gain.

Yes the bandpass filter peaks up quite nicely and I tested the transmit
function. I get about 150 mv pk to pk with just the pre-driver and the
audio sounds about right. I had to put a series inductor between the
crystal and the small 22 Pf variable to get USB. I used a about 10 turns on
a FT37-61 core. The balanced modulator works quite nicely for only two
diodes --I am used to using either a DBM like an SBL-1 or TUF-1 or an
active device like a MC1496. Two diodes and a coil are pretty cheap and
just as good. Today I will build the final amp and then give it a smoke
test.

Here is some coil data for you. I used FT37-43 toroids with a 13 turn
trifilar winding for the coils into the product detector/balanced modulator
and for the VFO mixer. I used a 13 turn bifilar winding for the pre-driver
and for the coils in the bandpass filter I used 22 turns on a T-50-6 iron
powder toroid. For the IRF510 final amp I will use 8 bifilar turns on a
FT-37-61 ferrite (~3 uhy). For the parallel driver stage I will use 13
turns bifilar on a FT37-43.

There are some very strong local stations here and that is where an AGC
circuit would be nice. Have you been thinking about an AGC modificaton.
Something simple where the voltage to the collectors on the receive vfo
mixer and post filter amp could be reduced based on received signal
strength. That might also enable an S meter.

Thanks again for a very nice project. I will let you know what I find in
the trouble shooting and when I get the final amp working.

73's
Pete W6JFR

_________________________________________________________________
Expressions unlimited! The all new MSN Messenger!
Change the way you communicate!

Hello fellow constructors!
What a good idea Hans to set up this group!
Just to say I am logging in and I am keen and excited to
start building this brilliant bit of kit!
All the best.

Duncan G4DFV

Hi all

My BITX20 is at an advanced stage of construction, but due to family
commitments I won't have very much time to finish it off over the next few
weeks.

I used a modular construction style, each stage of the transceiver is
constructed on a 2 x 1 inch (approx 50 x 25mm) of PCB stock in the "ugly"
style with no PCB etching. The modules are mounted at right angles to the
"chassis" which is also made from single-sided PCB. I have used tap washers
like the original, except for the transformers which are 15 turns
bifilar/trifilar on FT37-43.

The VFO works fine, I'm using an old variable capacitor and I removed 20
turns from the 150 turn coil to get the frequency range right. I noticed the
fine tune is rather non linear with voltage, and also much more effective at
the low end of the frequency range than the top. Something to investigate
further later.

I'm using one of my simple 2-chip frequency counters with 8 LED binary
readout of the frequency offset in 0 - 100KHz, 0.5KHz resolution. The cost
of this module is just UK ?2. See my counter page
for details (the Mk1 is in
my BITX20).

I have some photographs for you but it'll take me a while to sort them out
as I'm rather busy right now. Hopefully sometime next week I'll have them
ready.

72/3 de Hans G0UPL

Just a quick introduction - I'm David G3RYP and am currently building
the BITX20.

My usual breadboard construction method : a sheet of wood onto which
scraps of pcb are held by drawing pins - these also link the
groundplane between boards. Altogether very scruffy - but good for
making quick changes.

I've not made that many changes but am using an fet in the vfo and
toko coils rewound or t-50-6 toroids.

So far rx is working and only problems I've found is that the 50uf
cap in the collector of Q3 is definitely needed in my version -
otherwise lots of noise and not much signal. With the xtals I'm using
in the filter a 100p cap results in a nicer sound than when using a
220p.

I'm already thinking about a bit more gain and some agc but better
get on with the tx first!

Good luck to all.

Hi people,
havent been this excited about homebrew since I was a kid and built my
first (totally illegal) valve CW TX - thank you Ashar, do you realise
what you have started?
Have done the VFO and audio amp - perhaps others can post theirs as
well - if anybody wants info from mine, no problems, just ask.
I am using this project as a learning experience - the audio amp is
built "Manhattan" style using the NJQRP pad cutter, Used "Protel
Autotrax" (public domain) to do the layout for both - made up library
components with pad cutter clearance and then centre punched the pads
to a blank piece of board. The VFO - did the same method, but "joined
the dots and filled in the earth plane with a marker pen " method -
crude, but works - put the components on the copper side of the board
to make it easier to troubleshoot. The VFO works, but need to figure
out the correct no of turns. Being an amateur, I used the tuning cap
available, the section used is approx 20-200pf.
Looking forward to seeing others efforts and "borrowing" ideas.
73 de VK3BFA

the previous site has had too much traffic. now i
have setup a new site with unlimited bandwidth at
.

the new writeup has an updated circuit and also the pcb layouts. i am
pretty bad with the typos. so please send me the corrections.

- farhan

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