---------- Forwarded message ----------
Date: Sat, 19 Jun 2004 22:08:39 -0700
From: Pete Juliano <jessystems@...>
To: Ashhar Farhan <farhan@...>
Subject: Re: Fw: First QSO with the BITX20 Transceiver


Hi Ashhar,

For the crystal filter I am using 9.0 MHz computer crystals. I built a test oscillator and measured them with a frequency counter. Out of a group of 20, I found 4 that were within 50 hertz of each other. Those are the four in the radio. When I jumpered in a Commercial Filter to make a comparison, I didn't even have to touch up the carrier oscillator crystal so the HB filter has a very close center frequency to the commercial unit. The HB Filter does a nice job and is cheap --20 crystals cost me about $7 USD and within that remainder is another batch that could be used for a second filter.

Attached are several photos of my version of the BITX20 including the Linear Amp, an overall view of the boards with digital display and a close up of the main circuit board. Hopefully next week I will have it all in a box. The VFO and stabilizer are as large as the mainboard. I used sockets for all of the semiconductors so I could do a little testing of various transistors and IC's

The linear amp output filter has the following constants. 220PF, L1 which is 12 Turns of # 26SWG on an FT37-2 powdered iron core form (red core ~ 0.55 uhy). Then followed by a 220PF in parallel with a 330 PF (= 550 PF) followed by L2 same as L1 and then a 220 PF. The caps are ceramic on glass and rated at 100 volts. Really small caps. I used a 78L05 regulator and the bias adjust --I used what I had --a 25K ohm pot in parallel with a22K ohm resistor. Works fine. The linear amp board is 2inches X 2 inches (5CM X 5CM).

You will note two relays --one at the linear amp just like the schematic --but I also had to resort to a relay at the main board as there was a RF feedback problem. The second relay solved that problem.

The microphone is a low impedance --A D104 (lollipop) fitted with a Heil HC4 cartridge. I have a 25K ohm pot soldered right at mic connector and use that to set the mic gain.


The last two evenings 20 meters has been hot and the RX is doing a FB job. Despite my initial comments about receiver sensitivity it is more than adequate.

If I get a chance I may try my hand at an analog agc circuit.

Again a very nice radio and despite its subtle simplicity --it packs a lot of peformance.

I will keep you posted on my progress.

73's
Pete W6JFR

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:
http://www.hanssummers.com/radio/huffpuff/contents.htm

73 Hans G0UPL
http://www.HansSummers.com