[Boatanchors] SSB Generation - Phasing VS Filter Opinion Sought

Sat Jul 20 23:44:41 EDT 2019

To ad a little to this: My first SSB transmitter was a phasing rig that I
built when I was in high school way back when in the early 60's. I used part
of the circuits from the W2EWL and the SSB package and others. It wasn't
pretty but it worked.

To set up the sideband suppression I found the easiest way was to listen to
the opposite sideband signal in a receiver with headphones and talk into the
mike using the same phrase over and over. This lets you adjust for the best
of the average voice frequencies. And of course you need to switch back and
forth between sidebands to find the average between upper and lower
suppression as there is a slight phase difference between the two.
The problem with using a tone is that the phase shift is different for
different audio frequencies. If you set it up for 1000 Hz the suppression
will not be the same at some other audio frequency.
This also requires no scope or other test equipment.

Carrier suppression is also best accomplished by listening for the carrier
beat in the receiver. The problem with using an indicator, scope etc. is
that there is usually considerable hum in the audio especially with the
older equipment. It is often hard to distinguish hum from actual carrier
with a scope or meter. This is also true when adjusting sideband suppression
trying to watch a scope.

I still have a couple of Central electronics 20A exciters. I have also had
some 10B's and even an SSB JR at one time.

The interesting thing about the phasing rigs is that if you unbalance one of
the balanced modulators to insert carrier and switch to the DSB (AM) mode
where there is no sideband cancelation you have AM. If you unbalance the
other balanced modulator you have PM (phase modulation).

I think that the main problem with the HT32 filter rig back then was more
from the way the audio was tailored than from the filter as both the highs
and lows sounded bad.

For building a first rig I think the easiest way to go would be with a 9 MHz
filter. It can then be easily put on 80 and 20 meters with a single
conversion and a 5 MHz VFO (command transmitter as use with the 20A),

A phasing rig could also be built that would be satisfactory with modern
parts where you could maintain the audio phase shift much better than the
old stuff.

If you use a low frequency filter such as 455 KHz you will have to do double
conversion for bands much above 80 meters. If you use a low frequency VFO
such as the Collins then you run into the issue of needing a balanced mixer
and tuned/tracking IF and also a second mixer and heterodyne crystals.

The Heath Kit SB10 sideband adaptor was a direct (on frequency) sideband
adaptor. The main problem with it was very poor sideband suppression. If you
set up the suppression on one frequency it could be ok until you changed
frequency then the phase of the RF circuits would change and the suppression
would be compromised. Switching multiple bands mad things worse. Also
carrier suppression needed to be readjusted every time you changed
frequency.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of Robert Nickels
> Sent: Saturday, July 20, 2019 1:05 PM
> To: D C _Mac_ Macdonald; W9RAN at oneradio.net
> Cc: BOATANCHORS2 LIST
> Subject: Re: [Boatanchors] SSB Generation - Phasing VS Filter Opinion
> Sought
> 
> On 7/19/2019 5:19 PM, D C _Mac_ Macdonald wrote:
> > My 1st SSB rig was the W2EWL rig but I never knew how to align it to
> get rid of unwanted sideband.  Only had a cheap VOM!
> 
> Equipment manuals and handbooks were filled with complex oscilloscope
> screens and discussion of ripple and as a result proper alignment of a
> phasing rig eluded most hams.    But a clever New Zealand ham, Fred
> Johnson ZL2AMJ was able to see what everyone else had missed, and
> published a short note in the NZ ham magazine in 1972 that makes the
> process simple and requires only a sine wave audio generator and a
> simple output detector:
> 
> The principle is simple.  We all know that feeding a single audio tone
> into a properly aligned SSB transmitter will produce an unmodulated
> carrier output (this is how most filter rigs produce CW).   This is the
> desired outcome.
> 
> An improperly aligned phasing rig will have both carrier and opposite
> sideband imbalance.   If we inject a 1 kHz audio tone and the carrier is
> not balanced, the result will be AM - a carrier with a sideband
> separated by 1 kHz on either side.   The output detector that is
> attached to the transmitter is nothing more than a crystal radio or
> field strength meter that will demodulate this signal to allow a 1 kHz
> tone to be heard in the headphones (or amplified speaker as I prefer),
> no different than an AM transmitter will do.    Step one is to adjust
> the carrier null controls to elminate the 1 kHz tone.    This takes less
> time than it does to type this sentence!
> 
> With the carrier nulled there will now only be a  2kHz tone audible.
> This is the result of the desired sideband beating against the undesired
> sideband, which are 2 Khz apart with a 1 kHz tone.    Now the Audio and
> RF phasing controls can be adjusted to null the 2 kHz tone.   Switching
> between USB and LSB is necessary to reach the best compromise.
> 
> Thats's  it!   Two simple nulling adjustments, no oscilloscope or even a
> VOM needed.      And if you don't trust your hearing or wish to have a
> visual indication, just download one of the free audio spectrum analyzer
> apps for your smartphone or PC and it will display the  1 and 2 kHz
> signal peaks in real time.
> 
> ZL2AMJ is  known by many as the inventor of the "Tucker Tin Two",  a
> minimalist SSB transmitter using just two tubes, and was a leader in NZ
> amateur licensing for many years.   He became a Silent Key in 2015 but
> in a previous email exchange I asked him how he came up with this clever
> method that no one else ever had suggested.  His reply was "it just
> seemed obvious to me".   And so it is!
> 
> Fred's original description can be found here:
> http://tinyurl.com/y2qjgehr
> 
> 73, Bob W9RAN
> 
> PS:   A simple $50 rtl-sdr will also serve as a "poor man's spectrum
> analyzer" to allow direct viewing of HF signals and is a must for any
> workbench.
> 
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