I'm planning on building a DC receiver for use with the WSPR system. I will probably follow W3PM's lead and put a crystal filter between the antenna and the mixer. This will be a fixed frequency receiver aimed at one 200 hz slice of the 30 meter band.Of course, the big question is what mixer circuit I should use. I'll probably go with an SBL diode ring, but while perusing the literature, I again came across "The Russian Mixer" of Vladimir Polyakov, RA3AAE. Michael, AA1TJ, is a big fan of this circuit, and has been talking about it on Radio Havana Cuba. What a cool circuit it is! Just two diodes in parallel, cathode to anode. RF from the antenna goes in one side, and the local oscillator signal is placed at the other end. The LO signal causes the diodes to turn on and off on voltage peaks, effectively chopping up the incoming signal, producing sum and difference frequencies. LA8AK's drawing of one version of this circuit appears above. (Obviously OM AK didn't like this configuration, but it gives you the idea.)
The really cool part is that because you have two diodes, the "chopping" takes place at TWICE the LO frequency. This happens because on a positive LO peak one of the diodes conducts, and then, on the negative peak, the other conducts. So it is as if the mixer gate is opening twice each LO cycle. This allows you to run the oscillator at half the operating frequency, with advantages for stability and for the effort to eliminate common mode hum.
A while back I saw (somewhere!) a clever use of this circuit. LO was running at around 3.5 Mhz. With the two diodes in the circuit, it was a 40 meter receiver. They had a switch that could remove the second diode from the circuit. By throwing this switch, the RX went to 80 meters.
Does anyone remember this circuit? Where did it appear? SPRAT? QQ? Tech Topics? I can't find it.
I had the impression that OM Polyakov was active in the early days of radio. But some Googling shows that he is of much more recent vintage, still active and listed on QRZ.com. Here he is:
Hello Bill
ReplyDeleteIt was in Tech Topics, I have it the book "Amateur Radio Techniques" edited by Pat Hawker
My local friend PA1GSJ uses one in his 30 Grabber design
http://www.qsl.net/dl1gsj/html/qrssrx30.html
All the best,
73 de Jan , OZ9QV/PA9QV,
Wow, Jan’s link to PA1GSJ’s site is a treasure grove of information and links to other very interesting sites!
ReplyDeleteThanks Jan!
Thanks Rogier!
ReplyDelete73, Joachim pa1gsj
This subharmonic mixer is really great seimpple receiver. Som for more first hand informations let's look to original soruce: http://www.cqham.ru/prostoy_ppp.htm
ReplyDeletehttp://www.cqham.ru/rx_pobeda80.htm
And how does it sound? Yeap very good:
http://youtu.be/sbOqN_4Zrns
73 de YT1ZW
There is few more original variation of Polyakov 2 diode subharmonic mixer:
ReplyDeletehttp://us3iat.qrz.ru/shems/rx/rx.htm Look for RA3AAE (Vladimir Temofievich Polyakov)
http://www.chipinfo.ru/literature/radio/200301/p58-60.html
http://cadzone.ru/content/view/556/25/
http://pa2ohh.com/07swrx1.htm Holland version
Extensive search results can be achievede on www.yandex.ru by typing key words приемник полякова (receiver of polyakov)
73 de YT1ZW
ra3aae sub-harmonics mixers are very wonderful. on the first try it worked beautifully. i wrote experience on blog. vu3inj.blogspot.in.
ReplyDeleteDid you ever find the dirt on switching out one of the diodes on the Polyakov mixer ? Tnx
ReplyDeleteI don't know what you mean. What "dirt"? One diode gets you one band (serves an ordinary diode detector). With two diodes you get twice the LO frequency. There are lots of other blog posts about this. Good luck. 73 Bill
ReplyDelete