Very interesting ideas.

On the subject of VFO's, one addition I am going to make at some point on my
rig is a Huff Puff stabiliser. You can see my version, and read much of what
has been written about the Huff Puff stabiliser technique since it was
developed by PA0SDB in 1973, visit my page
. A year or two ago I
spent a day in the Science Museum / Imperial College library in London (I am
an ex-IC student in fact!). I had all the RSGB RadCom's bought up from the
archives on a trolley, and went through and photocopied all the original
articles and follow up. RSGB have given me permission to reproduce them on
my website. All that remains is to find the time to scan them etc. In any
case, these early articles are of historical interest but in practice you
will want to read the more recent articles if you are intending to build a
stabiliser. Again, the components are simple logic IC's and should be
reasonably easy to source.

On the BITX20@..., you will see that
Hans Summers (www.hanssummers.com) has a binary counter made
of two 74HC4040s. This seems ideal to me. I have avoided it
from the basic design to keep the construction challenge low.
I personally use my lab frequency counter along with my
transceiver for frequency spotting. I keep the counter
separate because i found that unless they are well sheilded,
the counter tend to generate a lot of noise that back
couples from the VFO into the receiver front-end.

My counter uses one 74HC4060 and one 74HC4040, not two 74HC4040. The
74HC4060 is used for the timebase because of its onboard crystal oscillator.
The URL is: . All these
components should be easily obtainable anywhere. Here in the UK the
component cost is about ?2. The old CMOS 4060 and 4040 should work just as
well, but the maximum count frequency will be lower. At the BITX20's VFO
frequency, old CMOS implementation would be fine.

I am in frequent correspondence with Onno PA2OHH who designed the original
3-chip version of the counter , which
inspired my modified and even simpler version. We have been sharing ideas on
the counters, a nice collaboration. He is currently performing some very
interesting experiments with a 74HC390 dual decade counter instead of the
74HC4040. With the 74HC4040 the LED's indicate 64, 32, 16, 8, 4, 2, 1,
0.5KHz. You get good practice at reading binary. With a 74HC390 it is easy
to obtain a different sequence: 80, 40, 20, 10 and 8, 4, 2, 1. The LED's can
be arranged in two columns of 4, one to indicate 10's of KHz and one to
indicate KHz. The mental arithmetic is faster and easier, but the resolution
of the counter worsens from 0.5KHz to 1KHz.

Note though that the intensity of the least significant LED acts as a kind
of analogue frequency indication, which makes it possible to estimate the
frequency to better the resolution by a factor of 2. For example in my
design if the LED is half brightness, it is possible to estimate that the
frequency being measured is xx,xxx,250 Hz.

Another advantage of the 74HC390 version is that it does not require the
100-count detect gate (3 diodes + resistor), nor OR'ing this 100-reset
signal onto the reset pin (2 diodes + resistor). Thereby eliminating a
further 7 components from the design (5 diodes, 2 resistors).

I have installed my Mk1 simple 2-chip frequency counter in the front panel
of my BITX20 and marked the tuning dial 14.0, 14.1, 14.2, 14.3 and 14.35. My
readout is now accurate using the dial for 100KHz accuracy and the counter
to read 0 to 99.5KHz. I have not yet debugged my rig so I can't yet be sure
how much effect it has on the rig. There is an on/off switch for the counter
so that it could be used to read the frequency then disabled. At the present
time I hear hiss in my headphones and a faint tone at about 1KHz (the
frequency of the pulse-width-modulated LED's) when the volume is at full.
But the counter has no shielding yet. I will report further results as and
when I have time to progress the project.

Another interesting observation: In my 80/40m polyphase receiver
I have installed my
8-digit frequency counter

as well as a 24-hour clock
. The counter
and clock are both built in screened boxes made from PCB stock, and they
each have an inductor in series with their power supply. Both of them
pulse-width modulate the LED displays to eliminate LED series resistor. Duty
cycle is 1 in 6 if I remember correctly. Both the clock and the counter have
their own on/off switches because I was worried about digital noise getting
into the receiver. But during extensive use I have never found it necessary
to switch off the counter or the clock, since they appear to contribute
nothing at all to the receiver noise floor apart from possibly the
occasional and very faint birdie. But even this I have been unable to
conclusively prove to myself.

Use of low current LED's in the 2-chip simple frequency counter and lower
duty cycle (I use 1 : 64) helps noise, because it means the power supply
smoothing is much more effective (all other things being equal). I am
currently trying (with only limited success) to source a 16 or 32KHz crystal
(yes KHz not MHz) to replace the 4.096MHz crystal in the counter, which I
hope will reduce the power consumption even more. For the fun of it I am
going to build a miniature version using one of the tiny 6mm long
cylindrical 32KHz crystals and surface-mount 74HC4060 and 74HC390.
Surface-mount, but "ugly" not on a PCB. I hope it will be about the size of
a postage stamp, and a few mm thick, with current consumption < 1.5mA.
Rather an extreme project and not recommended. But I do definitely recommend
the counter design, use more real-world size components!

73 Hans G0UPL

---------- Forwarded message ----------
Date: Thu, 24 Jun 2004 10:22:26 +0530
From: Ashhar Farhan <computercorp@...>
To: arvevans@...
Cc: farhan@...
Subject: RE: BITX20, 40 or 75 M versions?

dear arv,

you have spent a great deal thinking about the design and the possiblities.
it is wonderful to see that amongst us the natural need to push the envelope
is well and alive.

when i had declared to W7ZOI that the design is frozen, he was skeptical and
hopeful at once. he said, wait until someone decides to do things with it
that you hadn't even thought of. i guess the idea of an 'open source' design
like BITX20 is that you have a simple basic design that invites adaptation
and evolution.

very interesting points, you raised. let me give you my side of the story on
these:

(1) One could just change the frequency of the VFO and front-end
coils as you mentioned, but also the actual IF frequency could be changed
to minimize the possibility of 'birdies' from unwanted frequency mixing,
and to take advantage of whatever crystals were available cheaply for the
individual builder.

I didn't want to stray away from 10MHz crystals as they seem to be the
cheapest and most universally available of the lot. An interesting variation
is that you can use a 10.7MHz standard filter and the same VFO will cover 20
and 40 meter bands. Only the RF preselectors need to be switched.

(2) Use of an FET for the VFO as you mentioned in the web page is
also interesting, but the sometimes inexpensive availability of DDS chips
might make a digitally tunable unit possible for some hams (see SM0VPO's
simple frequency synthesizer for another cost effective approach).

this design was made primarily for Indian hams (although i dont know of any
who have started to build this in india yet). DDS chips are hard to come by.
The entire transceiver costs about 10 dollars to build in india. the DDS
chip costs much more.

this brings me to the issue of DDS. My personal taste is for purely analog
designs. It is a very personal choice. I spend most of my time writing voice
over IP software which is wholly digitally. For me radio is a way of getting
away from it all. I would rather spend the evening tempurature compensating
a low noise FET VFO rather than fight a noisy DDS. But again, it is a purely
personal choice. I have seen some pretty good cleaning PPL loops around a
basic DDS. If any, I am inclined to implement a Huff and Puff stabilizer for
the VFO as a add-on.

(3) A cheap microprocessor employed as a frequency counter (with
binary LEDs or 7-segment displays) would add digital readout capability.

On the BITX20@..., you will see that Hans Summers
(www.hanssummers.com) has a binary counter made of two 74HC4040s. This seems
ideal to me. I have avoided it from the basic design to keep the
construction challenge low. I personally use my lab frequency counter along
with my transceiver for frequency spotting. I keep the counter separate
because i found that unless they are well sheilded, the counter tend to
generate a lot of noise that back couples from the VFO into the receiver
front-end.

(4) Adding a dual op-amp to the transmit audio section could provide
some speech compression and/or audio filtering. I wonder if the same
compression and/or filtering could be applied to the receive audio with a
positive result? If obtaining a dual op-amp was problematic for some
builders, a couple of transistors could also be employed as a compression
circuit, and two more could be used for the speech filter.

the primary filtering is provided by the 10 MHz filter. that is why, the
modulator is so sparse. i think two back to back diodes could clip the RF to
provide better throughput. The trouble with this approach is that you will
have to switch this off for CW and PSK31 to preserve the gaussian shaping of
these keyed modes.

(5a) Conversion of the unit to include CW capability looks fairly
simple at first glance. Three options come to mind from just looking at
the schematic: (one) upset the balanced modulator via a keyed transistor
to load one side of it, or (two) use the key to drive a transistor switch
that bypassed some RF around the balanced modulator, or (three) key a
sinewave tone generator into the microphone input circuit. The latter
method seems more in keeping with the simplicity of the original design.

just upsetting the modulator balance might not give you a full carrier as
the carrier oscillator is set to the edge of the filter. a better idea might
be to add a sidetone audio oscillator and inject it into the audio amplifier
as well as the modulator. probably you can get the mic amplifier oscillating
with an RC feedback circuit.

(5b) Adding CW sidetone might involve leaving the receive audio
circuit powered up when transmitting CW and injecting sidetone audio to
that section. CW sidetone could be switched by the keying circuit, or by
detecting a small sample of the RF output and using that to "key" the
sidetone oscillator.

let me confess, most of my personal operating of BITX20 has been on CW and
PSK31. not ssb. I use a morse generating program running on my thinkpad feed
into the mic input of the BITX20. i do this because it allows to be leave
the BITX20 running at the other end of the table and continue my mng qth
work (i telecommute to work. my 'office' is a server in an underground
dungeon of rackspace in boston). if i hear an interesting station on CW, i
just have to switch windows and start a ragchew.

(6) Adding VOX capability could be accomplished by sending some of
the transmit audio to an amplifier, rectifier, and relay driver that
operated a small relay to replace the manual DPDT you used in the original
design. Anti-VOX circuitry would not be necessary if the ham were using
headphones instead of speaker for reception, or it could be added in the
form of a properly phased audio cross-over from received signal to the VOX
circuit.

i now have a two relays working in my own build. i control it through the
serial port of the my thinkpad. the thinkpad is programmed to do a lot of
things including run an AGC, generate morse, VOX and a bit of voice
compression. the code is messy and patchy. i will post this as soon as i get
some time from my mng qth.

(7) If one added CW capability and wanted QSK there are several
options for adding this function: (one) a CW sidetone could be injected
into an abreviated VOX circuit to operate a change-over relay, (two) The
key could simply operate a relay driver so that a small DPDT relay
performed the keying (use a hold-over timer to keep relay chatter to a
minimum), and (three) a more complex transistorized RX/TX switching scheme
could be devised to replace the manual DPDT PTT switch.

(8) If obtaining the LM386 audio amp were a problem for some BITX
builders, a comparable audio amplifier can be fabricated using a NPN & PNP
pair, driven by another NPN. About 1/4 watt of audio is available this
way...plenty for headphones or a small speaker.

quite true. and i should have done this. too lazy to solder an audio amp
together. there is one in the first chapter of EMRFD. i think i will post
that circuit on the site.

A BITX for 75 M also seems logical for US hams because a significant amount
of ragchewing contacts take place on that band. This could provide a
daytime local coverage method that augments today's use of 2 Meters for
local coverage.

Yes, 75M is too noisy in the tropics. In europe and usa, it seems to be the
preferred local band. plus, the indian cities are too congested for a 75M
antenna. 75M would mean using VFO at 13.5MHz or at 6.5MHz. If is always
preferable to have your VFO running on the higher side of the IF to reduce
the birdies but stability threatens. At 13.5MHz, you could use a VCO with a
10 turn pot to for tuning.

Since I also play around on the US LF band (the Lowfers group) the thought
occurred regarding a possible BITX for 160 KHz through 190 KHz. After I
get some experience with converting your design to 40 Meters I may try a
Lowfer version.

<Each band will require a different set of coils. If you have worked out
a
set, do send us the details. this information needs to be deciminated.

Thanks again for your reply and assistance. Your contribution of the BITX
design to Ham Radio is much appreciated. The layout represents an elegant
approach to a sometimes complex set of problems in the design and
construction of inexpensive but fully functional ham radio equipment. Have
you considrered starting your own company in India to construct and market
your designs? I suspect there might be a worldwide market for either kit
form or fully assembled single-band SSB transceivers if one could keep the
cost at a reasonable level. Your design also seems like a logical radio
component for interfacing with PSK-31, packet radio, or other computer
supported communication modes.

thanks for the kind words. i think far lesser credit should really be
attributed to me. most of these circuit blocks came off standard works like
Solid State Design and Experimental Methods in RF Design. W7ZOI gave me a
huge lot of encouragment and advice on making the rig better. For instance,
having a triple tuned circuit on the input was a small but very important
change (two capacitors and a coil) that remarkably improved the overall
receiver performance and transmission purity.

om hans summers has been an exceptional organiser who is marshalling us all
to gather together and get on with soldering. he is organising for
components, people and places. i am trying to source him with some key
components that are very cheaply available in india. thanks for dropping in
the email and do stay in touch.

73s,
- farhan

Thanks again & 73's

Arv
_._

-----Original Message-----
From: Ashhar Farhan <computercorp@...>
Sent: Jun 23, 2004 1:39 AM
To: arvevans@...
Subject: RE: BITX20, 40 or 75 M versions?

dear arv,

join up BITX20 group at . it is a forum of the
BITX20
builders.

No, as of now, i dont know anyone who has attempted to build it for 40
meters. but i dont see any reason why it should not work at 40Ms. i am
personally interested in a 40 meter version as most of the local ragchew is
on 40 in india.

it is a simple matter of substituting the RF filter and changing the VFO
coil to get it going to 40 meters.

- farhan




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

From: arvevans@...
Reply-To: arvevans@...
To: computercorp@...
Subject: BITX20, 40 or 75 M versions?
Date: Tue, 22 Jun 2004 22:58:50 -0600 (GMT-06:00)

Mr. Ashhar Farhan

Has your BITX20 design ever been built as a 40 Meter or 75 Meter version?
I am considering attempting a 40 M model, and if that goes well maybe one
for 75 M. If anybody else has already done this I would be interested in
contacting them to see what results they had.

Thanks,

Arv - K7HKL
-<arvevans@...>-

_________________________________________________________________
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The two extra sets are already accounted for! Seems I should have bought
more spares, but I didn't really want to be stuck with components and be
unable to do anything with them.

I can get more sets, but without the savings from getting 10+, 25+ and 100+
prices on some items, the price would be ?11.64 + postage (compared to ?8.19
for this bulk-purchased set). Alternatively, tell me you're interested and
we'll wait say until next Wednesday same time (13:00 UK time) and see how
many orders arrive. Perhaps get some quantity discounts again, if there are
enough more people interested. What do people think?

And if anyone needs any particular component and can't source it locally
(e.g. IRF510 being sent to Baino in Singapore) then I can sort that out for
you too, just email me.

72/3 de Hans G0UPL

I did a little bit of poking around, and found that Mouser offers these at USD$1.50 each, or
$1.24 in 100-pc quantities. For stateside users, it might be possible to set up a volume
buy and then distribute them -- US mail is $0.60. A 2 oz. Airmail Letter is $1.55 to India,
$1.60 to many places in Western Europe.

Mouser has no minimum order, but they ship UPS or Fedex, and it'll probably be around
$5.00 for the smallest size pkg.

I found some on ebay, but the seller's asking nearly twice the Mouser 100-pc price and he
also charges rapacious shipping.

For what it's worth ...

Jim N6OTQ

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Reminder everyone: deadline for orders for all the semiconductors + crystals
+ tuning capacitor + trimmers is tomorrow at 12:00 GMT (13:00 UK Time).

73 Hans G0UPL

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?

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?

Generally tap washers are used to fix leaky
taps/faucets. They are made of teflon or nylon and
vary from 1/2 inch dia to 3/4 inch dia, with a hole
in the centre which varies frfom 3mm to 4mm in dia.
The thickness varies from 2mm to 3.5mm in dia.
The size of the tap washers may vary from country to
country.

The best source for getting the tap washer would be
the local hardware store or your plumber.
Consult your plumber, he would direct you to the
right place to get the tap washers.

The BITX20 is a also a plumber's delight HI!

73,s
paddy vu2pep





__________________________________
Do you Yahoo!?
Yahoo! Mail - 50x more storage than other providers!

Thanks to Mark and Paolo for their replies. I am clear on "tap
washers" now and learned about "jubilee clips" too. I would have
called them "hose clamps".

73 Heinz, OE5EEP

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Hi ashhar, sorry to bother you but, I was wanting to know if 3uH
for T5 in the linear amp is across the total winding or from one
end to the centre tap. thanks kind regards. mark.

i calculated 3uH on each winding.

Don't forget Mark, it's a bifilar transformer with two windings, not just a
single winding with a centre tap.

73 Hans G0UPL

the 2N2218 is a fatter type of 2N2222. you can use
the 2N3866 instead. they are expensive in india.
but they might be easier to find elsewhere.

I can't get 2N3866 at any of my usual suppliers either! For now I'll keep
the 2N2219A in the list.

73 Hans G0UPL

The VFO and stabilizer are as large as the mainboard.

Pete, what VFO stabilizer are you using? Is it Huff Puff? I love Huff Puff,
and definitely intend to build a simple stabiliser for the BITX20 when I
have the rest of it working. See my Huff Puff page for details:


73 Hans G0UPL

Finally here's a full list of what I can order for you from Rapid
Electronics . Prices are the Rapid prices,
i.e. no profit for G0UPL :-( Postage is the price of a UK 1st class stamp
for UK orders (?0.28). Other countries will be extra at cost.

You must tell me your orders by this Wednesday at 13:00 UK time (12:00 GMT).
I will order on Wednesday from Rapid, receive the components on Thursday,
and send them out to you on Thursday. UK orders should receive them on
Friday, ready for the weekend's homebrewing! Don't send any money yet, just
tell me what you want and then wait until Wednesday when I have placed the
order at Rapid: it might become slightly cheaper still if we go over other
quantity pricing thresholds.

You can pay me by any of the following methods:

1. Paypal (preferred) to my email address. Anyone can use a credit card to
pay me this way, without needing to be a PayPal member, see
.

2. UK cheque or postal order

3. Cash: British Pounds, or if you like approximate equivalent amounts in US
Dollar or Euro. Not other currencies please, I am a homebrewer not a bank, I
can't handle Mauritanian Ouguiya or Azerbaijanian Manat.

If you are going to pay by 2 or 3 above, then I will send you my postal
address via email.

Rapid do not stock 2N2218 driver transistors, nor are they at Farnell
. However I have managed to find a different source
for supply of 2N2219A which is like the 2N2218 but has better gain
specification. I'm sure it will be suitable.

So here's the prices and description: feel free to take all items or only
those you think you need. To keep it simple, transistors will be in a set of
25 BC547B, and diodes in a set of 15 1N4148. This leaves a couple of
transistors and diodes left over for later modifications! If there's
anything else you need particularly then let me know. Varying the quantity
is fine too, e.g. take two IRF510's so you have a spare if you are worried
about frying them, or if you want to play with push-pull for higher output
power.

Prices are in UK pounds inclusive of VAT (sales tax).

?3.58 Qty 10 of 10.000 MHz crystals, HC49 style
?0.59 Qty 25 of BC547B transistors
?0.70 2N2219A driver transistor
?1.53 IRF510 MOSFET
?0.19 Qty 15 of 1N4148 diodes
?0.07 36V Zener diode
?0.05 9.1V Zener diode
?0.05 5.6V Zener diode
?0.29 LM386N-1 Audio Amp IC (correct variety)
?1.88 Qty 5 of 2-22pF trimmer capacitor
?0.71 Miniature tuning capacitor*

?9.92 total, if you wanted everything and including ?0.28 UK postage.

* NOTE: The tuning capacitor is one of the miniature kind as used in
portable radios. Size is 20.2 x 20.2 x 10.8mm. Control shaft is 6.6mm
diameter tapped with 2.6mm thread. Panel mounting is via twwo 2.6mm tapped
screws next to the control shaft. Capacitance: AM section 3.0 - 141.6pF,
Oscillator section 4.0 - 59.2pF. So in parallel you'd have 200pF which is
less than Farhan's design for 350pF. It might therefore be necessary to
alter the VFO coil to get the required tuning range.

73 Hans G0UPL

--- In BITX20@..., "Mark Jones" <Mark@H...> wrote:

Hi,
just joined the group. Hope I will have some time to build this great
RIG soon.

Hmm, good question. An American asked me recently what a "jubilee

clip" was

- that was a struggle.

A tap washer is a thin shim of rubber/nylon/fibre that fits inside a

water

tap (faucet?) - like in the bathroom - so that when the water valve is
closed there are no leaks.

Until 10 minutes ago I never knew about "jubilee clips". Then I
remembered our good friend Google has a good engine for searching
images:

Jubilee clip:


Tap washer:


Google images might help for other visual searches as well.
Thanks for the explaination Mark, and sorry for the off-topic,
Paolo

On Mon, 21 Jun 2004, david.g3ryp wrote:

I've taken the measurements you suggested and indeed it was the driver whose output was low - only about 1 volt peak. I was using BC549s throughout and although they tested ok when I changed them in the pre-driver and driver stages for 2n2369s the output from the driver went up to 4.5volts peak.

I've tried a variety of core types and none appears to be critical. I'm using a t-50-6 in the IRF510 drain - 14 bifiliar turns to get the 3uh you suggest. Know what you mean about winding these things!

The output without the lpf in circuit is 6.25watts but I need to adjust the bias for a standing current of rather more than 80ma to achieve this - although it may be that the balanced mod is not that well balanced (I haven't put in any caps yet).
I'll test this and let you know. Even without the lpf the output is quite a pretty sine-wave.

Now where does this 6.3 volt resistor fit in? Am I looking at the wrong schematic? Perhaps in the driver emitters? I'll try changing the 10 ohms to 5.6 or thereabouts and see if the output goes up.

The driver and prediver's emitter resistors are 6.2ohms (i used 5 ohms).

due to the feedback design, individual transistor types are non-critical.
the driver did require a heavier than BC147/2N3904 type of transistor.
The plastic package prevents one from being able to gauge their heating by
just touching them. until they are properly cooked.

the 2N3866 will do fine. the latest 'build' of the circuit is on
www.phonestack.com/farhan.

- farhan

Lastly thanks for putting a unit on the rf voltages. All too often schematics either don't contain rf voltages at all or they don't specify whether they're Peak to Peak or Peak or RMS - and there's quite a difference!

I think I'll change the other 549s for 2n2369s if I have enough just to see what happens.

Good luck to everyone.

David

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On Mon, 21 Jun 2004, jillian swannack wrote:

Hi ashhar, sorry to bother you but, I was wanting to know if 3uH for T5 in the linear amp is across the total winding or from one end to the centre tap. thanks kind regards. mark.

i calculated 3uH on each winding.
- farhan