Another idea.
Why not some sort of RF-probe circuit? It would look just like the RF probe
in the book, but with different component values to get the time constant
down. The RF probe in the book gives about a 100 Hz bandwidth which isn't
enough (I'd want at least 5K for SSB audio testing).
It seems different values might make this work (For SSB only, no BFO for
CW). However, I can't seem to get a decent audio signal off the top of my
dummy load. I've tried a bunch of different RC combinations, but I believe I
also need a blocking capacitor on the output.
I'll continue to fart around with the junk-box parts, but someone with a bit
more depth of knowledge might grap a calculator and drop in the values of
the parts I'd want.
Ant --- Cap (0.01) ----------- Cap (2) --- headset
| | |
diode R (5M) |
| | |
Ground ----------------------------------------
Of course, maybe my audio IS that bad, and this detector is working fine!
Dan / WG4S / K2 #2456
-----Original Message-----
From: John Magliacane [mailto:[EMAIL PROTECTED]
Sent: Thursday, November 11, 2004 4:58 PM
To: Dan Barker
Subject: RE: [Elecraft] How to set up SSB
Hi Dan.
> The simple reciever sounds fun. Any ideas what besides a 9v battery and a
> crystal I might need?
I made one once (for the actual purpose you are describing) using 2
MPF-102 FETs and a low-noise OP-AMP (LF351). I built the thing on
a protoboard.
The oscillator (I used a crystal inside the 160 meter band) was a Colpitts
design (common drain). The source of the oscillator fed the source of
the second MPF-102 that served as the mixer. The gate of the mixer was
fed by a parallel resonant circuit (tuned to the 160 meter band). The
drain had a resistive termination -- something like 1500 ohms to the
+ end of the power supply (a 9 volt battery). This was capacitively
coupled to the op-amp.
I don't recall what voltage gain I had the op-amp set for, but I had
no trouble driving a pair of hi-fi headphones.
Someday I'll toss something like this together again. I used this
receiver to run transmitter frequency response plots on my K2 last
year, and after making some changes to my KSB2 board, I'd like to
do it again to compare the results.
There's a way to monitor your TX audio through the K2 itself, (go to
CAL -> SSB BAL, and talk into the mic), but I think it bypasses the
crystal filter in the KSB2, but GOES THROUGH the post IF amplifier
filter (which plays no role in your TX audio response).
I sometimes monitor my signal using a Grundig YB-400 portable
shortwave receiver, but the DC receiver is by far the best way
to get an honest on-air sample.
73, de John, KD2BD
=====
Visit John on the Web at:
http://www.qsl.net/kd2bd/
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