KitsAndParts.Com Forum

I see you are converted over to the I/O pins also. They sure make it easy to connect and disconnect from the board. I use them on all of my builds.

One great thing about the smd parts, they are really cheap.
Leonard

I finished the BitX20 style transceiver. I made a short recording of the receiver portion. The TX part works but I haven't had a QSO yet.
You will notice in short order that there is no agc. So, the recording starts out fairly quiet and builds to a crescendo at about 1 minute and 3 seconds into it. Don't say I didn't warn you!
http://tomnyc.no-ip.org/audio/birx1.mp3

Tom, ak2b

I use the hex spacers also.

I mad a video last weekend testing a bitx20 version 3 lowpass filter, a wa2eby amplifier lowpass filter, and a 20 meter bandpass filter using my network amalyzer. The camera was goofing up and the focus came out bad so I won't put it up. I'll redo it in the next 2 weeks. The wa2eby amplifier filter, http://golddredgervideo.com/kc0wox/wa2ebyamp/index.htm  had less than .1 db insertion loss. I was really impressed.
Leonard

http://www.hellocq.net/forum/attachment … tid=152219
I used this amp from Dave Benson's rig which is mounted in the back of the previous picture. It puts out 4 watts and is built on Diz's project board. The LPF is to the right for 20 meters.
Ta Da. I also made my first contact with this rig just a few minutes ago, 19:45:00Z with a station working a QSO party. I had been calling CQ all morning without any results but just happened to hear Larry call QRZ. It is a lousy recording because I wasn't expecting to work anyone - but did have the recorder going just in case.
The clunking in the background is the foot switch used to key the radio.
http://tomnyc.no-ip.org/audio/1stBitXQso1.mp3

Tom, ak2b

What type of coax are you using between the boards?  From the photo it looks like RG59U (looks like fat snakes in the picture!).
Except for the coax from the power amp to the antenna, RG174U should be good enough, and is a LOT easier to tie into
a wiring harness.

I made another video called Bit-O-Bitx
The video url is http://www.youtube.com/watch?v=V_uBqbEV0-w

Tom, ak2b

wa2mze wrote:

The bi-directional topology seems natural for a transceiver at first, but there are two problems.  First, no receiver agc (or transmitter alc).  Not even a place to apply manual gain control.  Second, the required gain is NOT the same in both directions.

You are right on the first point - not quite right on the second. If you look at page 5 of Wes's article,
http://w7zoi.net/Bidirectional%20Matche … lifier.pdf you will see a chart for resistor value changes per gain. I my case, I dispensed with such logic, threw caution to the wind, and just built it. I was shocked that I heard anything from the receiver at alll Transmit RF was just about right at 0DBm for my version of Dave Benson's amplifier. I would go back and change the amp ahead of the receive mixer if I were to do anything. I think 7db of gain is plenty for 20 or 15 meters. Yes, you will be rudely reminded very quickly that this receiver has no agc. However, if I had built this transceiver for top performance, I would have dismissed this design all together.  Originally I built the ssb transmitter and was quite pleased that it worked. Naturally, I wanted to make it into a transceiver. I figured I would just complete the Dave Benson design (which is really quite a good one) using my Hycas agc/if amp and have done with it. But then I thought, well, I know it will be good, but the BitX with bidirectional amplifiers seemed more interesting. Here was a guy (Ashhar Fahran) who designed a rig with minimal parts so hams in other countries could easily duplicate it. Well, us yanks could easily duplicate it because parts are readily available everywhere. As a result, the BitX20 underwent a major overhaul and became a project that some of ham radios best engineers made refinements to. In any case the original idea has stayed in tact. I just wanted to give it the Diz spin. I knew from the beginning it wasn't the best performer in the world but then, neither is a direct conversion receiver. They still sound good. My version of the BitX sounds better and better every time I brag to someone that I built it myself .

Tom, ak2b

Hi Lee,

Well, bragging is over-rated. My Bit-o-bitx isn't long for the world. I don't really like ssb but I wanted to see if I could do it. I learned a lot in the process. I want to get back to a cw rig maybe using another type of frequency control like a VXO. The nice thing about using modules is that it makes experimenting easy. I also really like building on the empty boards like the Dave Benson PA and the bi-amplifiers. The board is just about the right size for a VXO .
I have taken a lot of good info from the K1 and K2. The schematics and circuit descriptions are a great source of information. Yesterday I just finished an SW20 from Small Wonder Labs. That is a clever little rig. I am now a big Dave Benson fan.
Lee, please keep us informed of your progress.
Tom, ak2b

Hi Lee,
When you say that your GDO will drive it to full power, are you talking at the normal input of the amplifier or at the base of Q4. T3 is a step down transformer most likely designed to match the output Z of Q5 to the input of Q4. Diz is far more capable of answering your question than I. But, I am curious where you are getting 1 watt from and why you no longer want to use D2?
Tom, ak2b

The HYCAS board works perfectly well, it’s just a little too big. I wanted something a little smaller in keeping with the Erector RX so I copied the K2 AGC stone for stone. Elecraft uses an NE602 to mix their 4.9 MHz IF with a 5.068 MHz crystal to 150 KHz, amplify it with an audio op-amp, rectify it and use it on the AGC pin of the MC1350. It is an interesting way to do agc.  I swapped the 5.068 MHz crystal with a 4.9 MHz one. The board works fine and pretty close to the original. I’ve always like the agc in the K2 in that it is a nice gentle curve rather than reaching a threshold and keeping everything the same level. Jack Smith did an excellent analysis of the K2 agc.
The only thing that doesn’t seem to work is the IF gain control. It doesn’t make much of a difference in gain regardless of where it is set (unlike like the K2). I don’t know how to fix this yet.


Tom, ak2b

Hi Gary,

Yes, I like the generic boards more and more. They actually are nicely spaced for size 802 smd's. You can buy smd's by the pound on the internet for very cheap. Here is another board I built up using a TriQuent AG302-86. They are $1.95 at Mouser. It is a handy dandy 16db gain block with a 50 ohm input/output impedance. It also comes in a slightly higher gain but the number escapes me at the moment. Pete, N6QW introduced me to these gain blocks. He uses two of them for a bi-directional amplifier that he has designed.




Tom, ak2b