message dated "Mon, 10 Aug 2015 13:30:46 -0500."
Here's how I still tune up at least for now. I have a
Halicrafter HT37. My receiver is a modern Icom R75 receiver but I
do enjoy using split transmit and receive for a couple of
reasons. On a practical level, if the transmitter blows up, one
still has a receiver.
Technically, one is supposed to be able to monitor one's
own transmissions and this can be done best by actually listening
to them if possible.
When you run separate TX and RX, you must use a TR or
Transmit/Receive switch or relay. Most transmitters either supply
a voltage to the TR relay or close a set of relay contacts that
have the relay voltage on one side of the contacts and the relay
coil on the other side. TR relays come in all kinds of designs
with many of them using a 120-volt coil and running on AC which
means you always need to handle the relay coil voltage with care
but it gets even more interesting.
I have, for example a Dow Key TR relay which is meant to
run on 120 volts but that's not how I actually do it.
A 120-volt AC coil has quite a bit of inductive reactance
which looks like series resistance when run on AC but if you run
it on DC, you can get the coil to pull that relay closed very
nicely on 30 volts AC. The relay doesn't buzz and it runs a lot
cooler plus there is no 120 volt power out there to accidently
contact.
The relay removes the receiver from the antenna during
transmit and instead puts the antenna across the output of the
transmitter. There is also a set of contacts on the relay that
corresponds to a mute or standby input on the receiver. Many
communications receivers have standby inputs on them for just
this situation.
The idea is that you don't want to hear your receiver's
audio while transmitting as it may cause feedback. Sometimes, you
do want to hear it if you want to monitor your own output.
I added a couple of special features to my TR relay
hookup.
First, there is a toggle switch that breaks the mute
circuit so that you can still hear the receiver audio during transmit
if the switch is open.
Another feature is a second toggle switch that causes the
relay to always be energized even if the transmitter hasn't
closed it's relay contacts.
Now, here's why these two switches were necessary.
The HT37 has something called Calibrate Mode. When you
are in that position, the transmitter sends out a carrier that
can be varied from no output at all up to a few watts. Most
people use that to zero their VFO to their receiver's frequency.
When in that mode, the transmitter does not close the TR relay so
my extra switch closes it and puts the weak carrier on to the
antenna.
Next, I disable the mute and then I can hear the VFO
output in the receiver. I may have to de-tune the receiver for a
beat note but one can easily hear it even though the receiver's
antenna is technically only a few inches of coax between the
receiver and the switching relay.
At this point, one can adjust the grid drive and plate
tank until the tone is loudest.
As I said, a test with someone actually watching the
output signal strength verified that this works.
Another thing one can do is adjust the phasing. The HT37
is a phasing sideband rig which means that the carrier must be
nulled out. I turn the microphone gain down to 0 and listen to
the receiver's audio for carrier. There's lots of stray noise so
you have to get used to what you are listening to.
If the two phasing pots are way out of adjustment, you
hear the noise I was talking about plus the tone of the carrier.
As you adjust the two pots, the tone nulls out and you're just
left with the noise. When you transmit, you can hear your audio
and get a pretty good idea whether or not there is a problem.
After that, I can flip both toggle switches to a normal
mode where the receiver mutes during transmit and the relay is
controlled by the transmitter.
In the seventies, I was a student at Oklahoma State
University and belonged to W5YJ which is OSU's amateur radio
club. Our HF rig was a Central Electronics 100V which was quite a
beast in it's day. It was also a phasing rig but like today's
rigs did not need to be tuned. You did, however, have to
sometimes null out the phasing circuit and I also did that by
listening to the transmitted audio.
That's one way to do things and I am sure many more
people have come up with such things as listening to their power
transformer's hum and, of course, the audio tuning gimics which
were quite useful.
As for how to stay on frequency. One feature that used to
be common on older receivers was the crystal calibrator. This was
a 100-KHZ crystal oscillator that was deliberately designed to
have a very dirty output full of harmonics.
If you cause the output to be a pulse wave form, one gets
harmonics well up in to VHF. So, you would hear a strong carrier
at every 100 kilohertz throughout your receiver's tuning range. I
remember a few rigs that had 25-KHZ crystal calibrators also so
you could use the 100-KHZ calibrator to count from some known
spot up to near where you needed to be and then switch to 25-KHZ
and count those birdies to as close as possible.
I never went outside an amateur band that I know of but I
sure got mixed up, one day, and got out of the General part of 15
meters. I called CQ and didn't get a contact and then realized
what I had done but never got a ticket. I think my signal was
probably too lousy for the FCC to mess with.
Martin WB5agz
> Attention all hams here on our list who have been hams going back into the
> 40's, 50's, and early 60's!!
>
>
>
> Post back to me and share with me how you tuned your transmitters and
> receivers back in those days. What kinds of creative methods did you use
> for, say, tuning up your transmitters with the PI output networks, dipping
> and loading, to make sure you were not only in resonance, but resonance on
> the right band? What kinds of techniques did you use to make sure you were
> within the frequency boundaries permitted by your license class and
> didn't
> get over into the Advanced or Extra Class frequencies, or outside the
> American band allocations entirely? What kinds of advancements or features
> were eventually added or available over time that made these kinds of
> tasks
> easier?
> Be as detailed and descriptive as you can. I am incorporating this
> information in a research project I am working on.
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