EMRFD Message Archive 14207

Message Date From Subject
14207 2017-08-10 18:08:20 jwolczanski LO drive
So, I'm scratch building the "Binaural Receiver".  I made a 3.5 MHz LO and used a doubler and a 2N3904 amplifier.  Ended up with 20dBm output into a 50 ohm load.  Nice clean waveform at 7MHz.

Mixers are home-brew on FT50-43 cores (15 trifilar turns) and 1N5711 Schottky diodes.

Even recognizing at least 3dB splitting loss - is 17dBm per mixer too much LO drive?

thanks in advance!

Warrenton, VA

14208 2017-08-10 18:28:13 Chris Trask Re: LO drive
Yeah, that's a bit too much. You might want to take advantage of that extra power by using two diodes in series for each leg, which would make it a Class II mixer. Better IMD performance.

>Mixers are home-brew on FT50-43 cores (15 trifilar turns) and 1N5711
>Schottky diodes.
>Even recognizing at least 3dB splitting loss - is 17dBm per mixer too
>much LO drive?


When the going gets weird, the weird turn pro
- Hunter S. Thompson
14209 2017-08-10 19:02:09 jwolczanski Re: LO drive
Perfect!  Thanks Chris, I was hoping for a silver lining!

Warrenton, VA
14210 2017-08-13 15:47:48 kb1gmx Re: LO drive
How did you measure that?  Both ports must be properly loaded and its not 
peak voltage but RMS (peak/1.414).

20 DBM is 100mW.  The output of the doubler is low enough that is unlikely
unless your running straight through (shorted diode?).

If you built as originally published your likely just getting enough.

14211 2017-08-13 17:58:17 jwolczanski Re: LO drive
Hi Alison

I did not use the oscillator shown in the KK7B article.  I opted for a oscillator running at 3.5MHz into a doubler. 

I used a doubler that was promoted by W7EL, using a pair of 2N3904's.  The output was too low (around 3mw if I recall correctly), so I used a tuned  amplifier from:
I used the one shown on page 5.

used a 50 ohm resistor as the load and hooked up the output to a scope.  Peak-to-peak divided by 2, times .707 - squared and divided by 50.  99 milliwatts.  I think the peak-to-peak voltage was about 6.3 volts.

Nice looking waveform too.

When listening to the 3.5MHz fundamental coupled lightly to the output, I got a nice dip in the doubler balance pot.  It was not at the mid-point.

I'm fine with using a series pair of diodes instead of one.....unless I get talked out of it.

Jerry W
Warrenton, VA
14213 2017-08-19 15:10:08 kb1gmx Re: LO drive
The publish design in QST just use a pair of fets at the desired frequency and put them in a tight can
for shielding.  

My miniR2 on 20M used the UVFO design at half frequency with diode multiplier and a J310 as 
post amp to a extended hybrid (hybrid with pi-networks on output.) its worked a chap for over 
a decade.  The only complaint I have is getting the VFO to settle down took time as I wanted 
under 50hz/hour at room temp.  Some N750 caps really helped.

There are a lot of ways to do this.