[ARC5] Netting Switch

[Dennis Monticelli]

I thought of using the switched load technique, but opted for something
simpler.  I addjust ed a small toggle switch on the T-22 front panel (this
unit was hacked before I got it so don't beat me up for drilling an extra
hole) that engages an internal 50 ohm dummy load resistor for spotting
purposes only.  It's only husky enough to survive a few seconds of tuning
up or spotting.  This  scheme gets me within 100Hz of the target unless the
SWR has crept up and the antenna is not 50 ohms anymore.   BTW, 2.7KHz is
the pull with a strong 1626 and 1625 pair.  It is greater if the tubes are
marginal.  As for the pulling of the osc when the PA turns on, that is
going to happen anyway whether or not the osc is left running.  That's just
life with a MOPA at 7MHz.  The chirp and drift will be worse if the osc is
keyed simultaneously with the PA.  It will be better if the osc comes on
with T/R engagement and stays on until the antenna switches back.  It will
be best if the osc stays on all the time and allow the inherent FSK to take
place.  On 80M, the inherent FSK may be too little and some extra
capacitance may need to be switched in during key down.

Dennis AE6C


On Mon, May 27, 2013 at 9:54 AM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 27 May 2013 at 9:12, Robert  Eleazer wrote:
>
> > It sounds like the best thing that could have been done with the WWII
> > Command Sets would have been to have a switching system where receiver
> > B+ was applied to the transmitter oscillators when they were not
> > transmitting, enabling them to run all the time and provide a weak but
> > readable signal so to allow zero beating the receivers with the
> > transmitters.
>
> Well, as a CW operator, I would have found that method to be very, very
> annoying. Leaving the transmitter oscillator running constantly makes
> effective communications on CW very difficult.
>
> Even at the weakest it possibly could be set, it would still mask weak
> signals.
>
> On AM, it would still be bothersome, although of course, not as badly. One
> would only hear the "weak" carrier when another station was "in there".
> However, it would still mask weak AM signals too.
>
> No thanks.
>
> That is not a good method for netting.
>
> Effective netting requires the transmitter oscillator to be able to be
> turned on
> and off for netting, AND to be stable enough to not be off that frequency
> when controlling the transmitter.
>
> Or one could use an FSK method to move it so far off frequency at key up
> that it couldn't be heard. But then for netting, one would have to arrange
> the
> circuit to shift the oscillator to the transmit frequency during netting.
>
> I am quite surprised that Dennis' T-22 pulls 2.7 KHz off frequency when
> driving the final amp. That would not be acceptable to me, although he is
> essentially using the FSK method mentioned above, so it works for him.
>
> One method to deal with this sort of thing "back in the day" was to switch
> a
> load onto the oscillator when it was keyed alone that would exactly mimic
> the
> load that the transmitter provided when driven by the oscillator.
>
> In fact, when power supplies had very poor dynamic regulation which caused
> frequency shift when keying the rig, some operators would use a double-pole
> relay to connect a load to the power supply at key up that drew the same
> current as the transmitter did at key down. This also minimized chirp
> caused
> by that poor dynamic regulation. Keying speeds were usually pretty slow,
> though.
>
> Ken W7EKB
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