[ARC5] Measuring sideband suppression. (Was BC-458 based SSB rig)

[Leslie Smith]

Hello Robert,
I'll give a complete (and short) answer to your question tomorrow
morning.
The longer answer is found (I hope) in the original article:
http://www.karinya.net/g3txq/temp/tucker_tin/

Suppose your SSB rig has 20dB sideband suppression.
Let us suppose the carrier is 60 dB suppression, and the carrier
frequency is 2000kHz (2.000MHz)
First you transmit with no modulation.  You adjust the RF phase shift
network for minimum carrier.
It should be possible to get 45 or 50dB suppression for the carrier.

Then feed a audio tones into the phase shift network.
With some help from your CRO (and Mr. Lissajous) you check the phase
shift network give 90 degree shift between the two audio lines.
You do this from (say) 250 Hz to 3000Hz, watching the trace on the CRO.
(I'm sure you've done this yourself, already)  90 degree shift?  Great!

Then you pick a tone, say 2000Hz
The sidebands will appear on 1998.0 kHz (LSB) and 2002.0 kHz.
If the LSB is desired the USB will be 1 watt, but still easily heard as
a 4000 Hz tone.
You tune the set to minimize the unwanted sideband.

The method is based on a clever understanding of SSB, and what happens
in the non-ideal world.
That's the general idea, but I'll get ZL2AMJ's description soon, in his
own words.
The tucker-tin is a great little rig - and you don't have to build it
in a cake tin,
 - you can build it on a proper aluminium chassis.

New Zealander's are nice fellows, and good at climbing Mt Everest or
sailing boats in yacht races or playing rugby - but really!
Who would build a radio in a cake tin?  Hardly proper, is it?


73 de Les Smith
[1]vk2bcu at operamail.com


On Sun, Nov 17, 2013, at 14:35, [2]WA5CAB at cs.com wrote:

  Les,
  Are you sure that it wasn't 500 Hz and 1500 Hz?  That's what you
  would get if you ran 1000 Hz audio into a DSBSC transmitter (or an
  SSB one with poor sideband suppression) if you tuned a receiver with
  adequate bandwidth to the suppressed carrier (center) frequency and
  offset the BFO by 500 Hz.  To get 1000 and 2000, you would need a
  1500 Hz modulating signal with the BFO offset 500 Hz.
  In a message dated 11/16/2013 20:47:47 PM Central Standard Time,
  vk2bcu at operamail.com writes:

  Hello Mac,
    Fred Johnson (ZL amateur operator) published the design of a
  phasing
    rig known as 'the tucker-tin'.
    I built one, and the SA amateur society sold 1000 of this 80m
    transmitter (as a kit).
    Now to the point of your "Q".  Fred described an arrangement to
    suppress the unwanted sideband using a diode detector, 'phones and
  a
    1000Hz tone (sin) generator.
    I've seen others describe the same method.
    In effect you listened for two tones (1000Hz and 2000Hz).  You set
  the
    RF phasing components to minimize one tone.
    By measuring the relative level of the 1000Hz tone and the 2000Hz
  tone
    you can know the sideband suppression.
    It's easy to get 30dB unwanted sideband suppression.
    I got 35 dB suppression.
    You'll work hard to get 40dB sideband suppression.  If your PEP is
    100W, a suppression of 40dB is 10,000 down, so 100,000(mW)/10,000
    equals 10mW of unsuppressed sideband.
    If you have an interest, I'll find the article.
    73 de Les Smith
    vk2bcu at operamail.com

  Robert Downs - Houston
  wa5cab dot com (Web Store)
  MVPA 9480

References

1. mailto:vk2bcu at operamail.com
2. mailto:WA5CAB at cs.com

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