> Phil put forward the idea of making a very simple 1.8MHz-only
> transceiver, with a tuned Cohen filter in the front end (see Peter
> Martinez G3PLX's famous 'Plagiarise and Hybridise' articles in the
> RSGB bulletin in the 1970s), virtually no RF amplification, a high
> level mixer, a single 455 kHz IF with 500Hz crystal filters at each
> end, and, finally a 'hi-fi quality' audio amplifier (a 20W-plus chip
> run at a low level. The VFO could be a direct digital synthesiser, or
> even an analog VFO (i.e. no phase noise whatsoever).
With no RF amp, it is possible to get into the -130dB or better
range on sensitivity. But the biggest problems are actually poor
filtering, poor gain distribution, and simple design errors.
Narrow filtering is too far back, after far too many semiconductors
are passed. Transmitters are not good either.
While I have saved a reasonable amount of money to spend on a
new radio, I certainly can not find one I would consider purchasing.
The current wave of transceivers are no better than most older ones
when receiving, and making matters worse the CW transmitting
characteristics remain poor and are difficult to correct. I care less
about 100 selectable filter shapes when the earlier stages block or
overload, I just want a good clean reliable basic radio with a few
useful filter bandwidths.
I'm especially disappointed the newer radios that will slowly replace
the current radios have the same or even worse key-click issues as
older radios. It is a shame little pressure is being applied to have
manufacturers correct design or performance issues like key
clicks. With properly filtered CW, there is NO reason to hear a
click more than a few hundred Hz away.
I hope the major manufacturers wake up soon. It might be a good
idea to remind them at every opportunity we actually want
transmitters without clicks that have good close-spaced
performance.
73, Tom W8JI
W8JI@contesting.com
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