I think Carl answered the why of not keeping the bandwidth center frequency
fixed as you change SSB widths. Another way of saying what Carl did is, you
would go below zero frequency under some conditions and see the aliasing
frequency folded down from the upper frequency ranges.
Now as to floating a speaker. That is an excellent way to REDUCE RFI.
Another reason, is they may be using a bridged audio amplifier, saving the
cost of a transformer, and distributing the power load to more than one
active device, thus reducing localized heat sources. It is not too hard to
run a zip cord to an external speaker, or even a shielded cable, the main
thing is to avoid grounding to the case of the radio, transmatch, etc.
If you have too many things external to the radio also grounded to station
ground or AC ground, (case ground), you can pick up computer hash thru
ground loops, and pick up RFI, etc.
Ten Tec rigs traditionally have been able to operate into SWR greater than
1:1, without folding back power until you get above 3:1. Mine do well
without use of a transmatch over the whole of the phone bands. Any
transmatch only introduces losses. I like to use resonant antennas, and
have fewer losses. There are good design ideas for either approach, to
always have a transmatch, or not. It all depends on how the individual uses
their radio, their antenna farm, etc.
It would be useful to describe to the list where you put the choke core to
eliminate your RFI from the keypad.
Was it close to the pad itself, or close to the rig, or somewhere along the
cable, and how many turns?
Few Yaecomwood noise "limiters" really work on the noises I have wanted to
fix; that is a "ham holy grail" that may never be possible to overcome
without a lot of extra hardware. Each of us has our own hearing, and thus
audio is best shaped by equalizers for our own transmit and receive
perception of what sounds "good". Often hams use way too high a fidelity
earphone for receivers, and hear the on board rig computer. The best radio
headphones I have are NOS 1955 vintage double magnetic phones of 15,000 ohms
impedance. They are so sensitive, you do not need to turn audio up, and
amplify the low level computer stuff. Also, their fidelity is limited to
the voice bands, for more intelligibility. For cushions, since the original
rubber snap on covers are not made, one can go to a drugstore cosmetics
dept. and find disks of sponge material. cut a hole in the middle of two,
and apply double sided scotch tape to the ear piece of the mil phones.
Stick the flat sponge pad onto the hard rubber of the earphone, and they
will be very comfortable once you adjust the head band to your liking. The
cosmetic powder cushion pads come two or four to a package, thus you can
replace them at low cost when they wear over time. Keep the spares out of
sunlight, and tube light range to preserve the sponge spares until use.
GL and 73,
Stuart K5KVH
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