I was looking for a good portable shortwave radio. I had been using a cheap
Sharper Image one made by Kchibo and a Grundig Travel Radio III. Both
didn't seem to perform too well but I also live in Southern California. I
bought myself on ebay a used ATS 404 and was wondering how well it
performs in comparison to other shortwave radios out there in the same
price range. The Paasport to World Band Radio liked the ATS-505 and
ATS-606 but thought the 404 wasn't as good.

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Klingonmastr schrieb:

I was looking for a good portable shortwave radio. I had been using a cheap
Sharper Image one made by Kchibo and a Grundig Travel Radio III. Both
didn't seem to perform too well but I also live in Southern California. I
bought myself on ebay a used ATS 404 and was wondering how well it
performs in comparison to other shortwave radios out there in the same
price range. The Paasport to World Band Radio liked the ATS-505 and
ATS-606 but thought the 404 wasn't as good.

Indeed, the ATS-404 does not tend to rank all that highly, even in
Amazon user reviews. This is not without reason, as it is a single
conversion set that is not in the same league, technically, as a '505 or
'606 (or a similarly-priced KA1101 or 1102). It should still be a decent
performer, if nothing too exciting - but then I guess you probably
didn't pay a fortune for it either.

The concept is quite interesting anyway, and since I found a service
manual on the web, I'll drop a few words on the inner workings for the
technically minded:

Relevant semiconductors
=======================

TA7358AP (FM preamp, LO & mixer)
2SK193 (FM IF amp, AM RF amp, common source in both cases)
TA8132AN (FM IF/discri/stereo demod, AM RF/mix/IF/demod)
TA7376P (stereo audio amp)
TC9318BF (microprocessor, LCD drive & PLL)

FM section
==========
Nothing overly exciting here. Frontend pretty much as per TA7358
datasheet, FM IF amp, a single wide ceramic filter (MA8, that's 280 kHz
selected for less ripple and flatter group delay - a 180 kHz MS3(G)
would give some selectivity to speak of at least), then the TA8132AN
with ceramic discriminators for IF, demodulation and stereo decoding
work.

The audio section with some audio filtering and the power amp follows.

AM section
==========

There is some (electronic) switching going on in the frontend, as the RF
amp is used for MW and the two (internal) shortwave ranges. Finding a
tuned ferrite rod for MW is not unusual, but there are some differences
between the shortwave ranges. On the first one (2.3 to 7.35 MHz), there
is a resonant (tank) circuit between antenna and RF preamp, while on the
second one (7.355 to 26.1 MHz), the respective tracking filter circuit
goes *after* the RF preamp, presumably to achieve better sensitivity. In
any case, these tracking filters must be aligned well for optimum
sensitivity.

Then comes the TA8132's mixer, not exactly a miracle in terms of strong
signal handling in my experience.

IF filtering is performed by an LT455H ceramic filter (a nominal 6 kHz,
6-element job) plus tuned IFT. That should give pretty decent
selectivity.

Then it goes back into the TA8132, AM detector and all, followed by the
audio stage again.

That's it, as far as the direct signal path is concerned.

Stephan
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