On Dec 3, 4:58*am, Ian Jackson
wrote:
In message
, writes

In the 1980s and 90s, I was intimately involved in many types of CATV
set-top boxes from one manufacturer. I would have thought that, even
after 10 years, I would remember to the nearest Hz what the oscillator
and IF frequencies were - but I'm afraid I can't!

However, the general plan was essentially that entire input spectrum was
bandpass filtered (via a cascaded highpass and lowpass filter), and
presented to a 4-diode ring double-balanced mixer. I'm pretty certain
that one model (50 to 550MHz) had a first IF at around 650MHz, with the
LO running from 700 to 1200MHz. This was then down-converted to a second
IF - the usual 45.75MHz (for NTSC).

All I know about the little tin-can tuners made by the billions in the
80's and 90's, is that antenna comes in one end, circa 45MHz IF came
out the other end :-). Maybe the ones I saw were not the DC-to-
daylight ones used for CATV. The generation I'm most familiar with
took a tuning voltage that went up to 30V or 40VDC for the varactors,
maybe that high voltage gave them a wider range with simpler
circuitry. Of course the line-operated ones had that high voltage
around for easy use in the chassis.

For most 'amateur' purposes, there is no need to have any ALC applied to
the output signal.

Look at the Elecraft K2's LO system. It uses a single VCO to cover all
bands, and one relevant factor that lets them use the same oscillator
for all bands is the ALC. It's a very very clever design, one that
minimizes not only parts count but the low parts count also means low
power consumption (less than 200mA for the whole rig in receive.)

Contrast that with, say, modern Japanese HF transceivers which draw
ten times as much power in receive and have these ginormously
complicated multi-loop synthesizers that in the end have worse phase
noise than the K2's simple scheme.

My gut feeling is that the Japanese rig philosophy of making sure
their receivers do DC to daylight drives up their parts count
enormously with no benefit (perhaps a negative effect) on ham band
performance. Maybe that's what the Japanese hams want. Heck, it's
probably what most US hams think they want, if for no other reason
than because the YaeKenCom ads have been pushing it as a feature (not
a bug) for decades, at least as long as they've been doing
upconversion ham receivers.

Of course the K2 does so well in comparison because it applies the ham-
band performance simplicity philosophy not just to the LO chain but
throughout.

Tim N3QE