G8MNY  > TECH     28.11.21 08:30l 77 Lines 3610 Bytes #192 (0) @ WW
BID : 54297_GB7CIP
Read: GUEST
Subj: SSB Demo circuit
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 211128/0927Z @:GB7CIP.#32.GBR.EURO #:54297 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                          (Updated Dec 04)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Being involved with ham training, I have been doing all the techical demos
including AM & FM (Sigen), but I was ask to do a SIMPLE demo of SSB generation
which my siggen can't do. As I only have a wide 50kHz bandwidth filters in my
spectrum analyser scope adapter & wanted to show the sidebands etc, normal
comms SSB is out, so I came with this set up....

               旼컴>SCOPE AF컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴
                                          旼>SCOPE DSB & AM컴컴컴컴커Y1  쿧2
                               D1                   旼컴컴컴커    旼컴컴컴
                         旼캑<쳐컫컴컴>o컨68鴛o<컴캑SPECTRUM쳐>X  SCOPE 
旼컴컴커 u1                    |)      o     o    쿌NALYSER쳐>Y 쿏ISPLAY
쿌F OSC쳐늘컫컴좔4k7컴쩡캑   T1 |)컴   __   __     ADAPTOR    읕컴컴컴
0 - 2V   4k7        ===       |)    ---------    1-90MHz
100kHz            1n  읕캑>쳐켸    ---------   읕컴컴컴켸
읕컴컴켸   0-5V  旼컴컴좔컴커   D2            
           DC    쿝F SIG GEN        쳐컴컨컴컴컨컴
                  21.4MHz         __   21.4 MHz
                  100kHz         ///  XTAL FILTER
                 읕컴컴컴컴켸

I cheated with 100kHz for the Audio to solve the analyser display problem. I
initially built from junk on just 2 BNCs, but I soon boxed it up. Diodes D1 & 2
are any small silicon type, I did find proper mixer types better (more linear)
but could only handle low level, but my scope was happier with larger signals.

T1 is a medium sized ferrite bead 6mm dia with 2x 8 turns (bifil) wound on it
with the centre tap (opposite end of each wire) earthed.

The filter I had is a 7.5kHz wide one (narrower than the spectrum analyser
resolution) & it is totally unmatched, but works well with only a 68 to
equalise the loss for filter bypass (DSB) mode.


SPECTRUM DISPLAYS

CARRIER              AM                 DSB                 SSB   
Y                                                     (upper or)
                                                        (lower) 
  컴컴컴좔컴컴     컨컨컨컨컨컨컨      컨컨컨컨컨컨컨      컴컴컴컴좔컴컴 X
                     | |             Mixer|/     \ Carrier
                  Over Mod         Distortion      Nul
                  Products

SCOPE DISPLAYS
                    /'\     /'\          /'\     /'\          /'\     /'\
AF-------------   AF   |   |   |       AF   |   |   |       AF   |   |   |
Y1                      \./     \./          \./     \./          \./     \./

                      _       _           _   _   _   _
RF같같같같같같   RF/' `\._./' `\._    RF/ \./ \./ \./ \    RF같같같같같같같
Y2같같같같같같     \._./' '\._./'       \_/'\_/'\_/'\_/      같같같같같같같
                                                |
                                            Crossover
                                             Nuls

AM can be displayed by off setting the balance of the mixer with DC.

I found the Scope display worked best with 1-10kHz AF & the Spectrum display
with 100kHz AF as this gave clear sideband signals (& distortion products in
course) & it was easy to select either upper of low sideband with 100kHz off
set of the RF signal generator.


See also my tech buls on "Spectrum Harmonic Demo circuit", "Scope RF Trick",
"Tuned Circuit Scope Demo" & "Oscilloscopes".


Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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