This particular transmitter is a 1980s synthesized radio using the
filter method to generate SSB. I will look up the manual and see how it
is rated for spurious emissions. Since it was built for government and
commercial use, I am sure it had to exceed any applicable FCC
requirements. My guess is that it was used for SSB communications
almost entirely. It is definitely in the boat anchor category as far as
weight is concerned, about 50 pounds. The front panel has 6 knobs that
are set to frequency, if you need something other than a 100 Hz channel
you pull out another knob and it allows altering the frequency by a few
hundred Hz.
The 1958 vintage 32S-1 is the only other rig that I have owned that
definitely used SSB mode and inserted an audio signal to produce CW.
That one did have some spurious signals, Collins produced a bulletin
about converting it from a dual diode mixer to a ring mixer to correct
some of the problem, then the 32S-3 went back to keying the RF directly.
Seems to me that the only real difference is just how low is the minimum
frequency signal. As someone mentioned, if you are generating CW by
having the DSP generate a 16 kHz signal and mixing it up to the output
frequency, the filtering to remove the harmonics and opposite sideband
are the same as if you used a 16 kHz audio signal to a rig operating in
SSB mode (with the filter offset to pass the audio signal). It seems
Collins used 800 Hz for the 32S-1, so the carrier was not far down on
the filter curve, in addition isolation on the balanced mixer was not
good. The opposite sideband did not seem to be the problem, you didn't
notice the 1600 Hz signal caused by mixing the two sidebands as it was
covered by the 800 Hz audio caused by the CW/SSB signal mixing with the
carrier.
I think I remember seeing a design from the early days of SSB which used
a tuned filter to remove the remaining carrier from the SSB signal. The
filter was like the old 455 kHz crystal filters in receivers from the
early 30s up into the 50s.
Further off subject, an old friend was working a CW contest when someone
nicely told him that he had a spur about 20 kHz down, he thanked the
fellow and told him that he would put a receiver down there and work
calls on both frequencies.
Thanks,
Barry
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com] On Behalf Of Ken Brown
Sent: Tuesday, April 26, 2005 12:18 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] cw creation
Sounds like an interesting rig.
If the 1 kHz sine wave has some harmonic content (it is not perfectly
sinusoidal), this rig could generate as many as five signals:
1) the desired signal 1 kHz above the indicated frequency
2) the second harmonic of the tone generator would still be inside the
SSB filter and would be a signal 2 kHz above the indicated frequency
3) the "carrier" which should be well suppressed, but often is not
4) the opposite sideband of the desired signal, 1 kHz below the
indicated frequency
5) the opposite sideband of the second harmonic of the tone generator,
2kHz below the indicated frequency
3, 4, and 5 are supposed to be greatly suppressed if the rig is aligned
properly. Number two depends on the purity of the tone generator.
If it is a phasing type SSB rig that doesn't use a sideband selecting
filter, there could be more harmonics from the tone generator, each
another 1 kHz further from the indicated frequency, and more on the
opposite sideband too. Phasing type SSB rigs do get out of alignment and
the opposite sideband rejection gets poorer, as well as the carrier
rejection.
In many cases I think it would be easier to use another BFO crystal and
unbalance the balanced mixer. There are fewer things to go wrong.
Yes, using the tone modulated SSB transmitter method can be done and has
been done. This is not exactly "a great many rigs", but there are no
doubt more. Do you know of some more?
>I have an ex-embassy commercial transmitter, the Sunair GSE-924 that
>injects a 1 kHz sine wave while in USB mode to produce CW. This is a
>pretty impressive rig, no cooling fan 30 w AM, 100 SSB and 100 CW. I
>have an idea that it was not much used in the CW mode. They do warn
you
>that the transmit frequency is 1 kHz above the indicated frequency
while
>in the CW mode.
>
DE N6KB
>
>
>
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