EMRFD Message Archive 4197
Message Date From Subject 4197 2010-02-04 17:57:35 bcdlr LO for DC RCVR & DSB XMTR My first big question: can you use the same LO for a DC receiver and a DSB transmitter?
I have completed a K5CBQ Si570 frequency synthesizer and wanted to use it as the VFO for a 17m/15m DC receiver - DSB transmitter combo.
If that is practical or possible.
I'm not an RF engineer - so please have patience with me. I've done a very early version BITX20 with outboard VFO and Manhattan PA/final board. I'm learning and Soldersmoke (book & podcast) has gotten hyped about doing something like this.
Dan Reynolds KB9JLO
4199 2010-02-04 23:15:15 Dave - WB6DHW Re: LO for DC RCVR & DSB XMTR bcdlr wrote:
> My first big question: can you use the same LO for a DC receiver and a DSB transmitter?Dan:
> I have completed a K5CBQ Si570 frequency synthesizer and wanted to use it as the VFO for a 17m/15m DC receiver - DSB transmitter combo.
> If that is practical or possible.
> I'm not an RF engineer - so please have patience with me. I've done a very early version BITX20 with outboard VFO and Manhattan PA/final board. I'm learning and Soldersmoke (book & podcast) has gotten hyped about doing something like this.
> Dan Reynolds KB9JLO
Answer is yes. You can also use the same mixer.
I designed and sell my UHFSDR transceiver which uses the Si570 and 2
dBM's (it can decode SSB as well as DSB) from 1.75MHz to 700 MHz. It
requires a computer with a sound card, but you could use a single mixer
and audio amps for DSB and CW with no computer.
Dave - WB6DHW
4201 2010-02-05 02:49:07 Johan H. Bodin Re: LO for DC RCVR & DSB XMTR Dan Reynolds KB9JLO wrote:
> My first big question: can you use the same LO for a DC receiver and a DSB transmitter?Hi Dan,
yes you can! I did that in my Optimist-80 DSB transceiver many years
ago. A single NE612 serves as VFO and mixer for both TX and RX. The
schematic is here:
Click "Preview the Optimist 80 schematics".
This is an old design with much room for improvement but it works quite
well. If I had to build another one today, I would replace the
power-hungry class A PA with a simple push-pull circuit using a couple
of small transistors (2N3904 style) on each side. Something like
SM0VPO's design http://www.vk2zay.net/article/4 but with 2x4 transistors
(or so). I have found this kind of amplifier to behave surprisingly
well, probably because of the 10 ohms (or so) emitter degeneration
resistors. Another advantage of the large emitter resistors is that
transistor Vbe matching is not very critical, biasing is easy and the
idle current does not change much with temperature. Need more power?
Just add more transistors and change the turns ratio of the output
transformer (the input impedance will decrease too).
Oops! I got carried away, far away from topic... :-)
4203 2010-02-05 09:03:19 bcdlr Re: LO for DC RCVR & DSB XMTR Dave & John, both of your designs are interesting. Really interesting kit there Dave.
Both of you though shared the mixer - can you just send the LO/VFO signal to both mixers? Do I need some sort of isolation - pardon me here, I'm struggling. New territory but exciting nonetheless.
My present plan is to use the DSSC generator from W1FB's QRP Notebook, pg. 138- for the DSB transmitter - might swap out the speech amp or modify to use an electret mic. For the Receiver I like the 8.5 modular DC receiver, pg. 8.13 from EMRFD and then finally for the amp I was going to use Farhan's JBOT amp. I have an old, old Kanga T/R switch to use for that part - been looking for a place to use it! :-)
That's my plan anyway. I want it to work, of course, but I have no grand dreams other then doing it!