[IRCA] Digital Superadio Plus

["kevin - Gilbert, AZ" <amfmdx@xxxxxxxxx>]

On 5/15/06 10:45 AM, "Patrick Griffith, N0NNK / WPE9HVW" <AM-DXer@xxxxxxxxx>
wrote:

> I've never seen a digital readout version of the SR. That seems like it
> would have been a good idea unless the circuit was noisy.

There really was a digital readout version of the SR.

http://mysite.verizon.net/vze20h45/radio/superadio/gesr_plus.html

The Superadio Plus: A Report
T. David Zimmerman

I have been a long time fan of long-distance performance radio receivers. As
a matter of fact, I collect many such radios which were made by American and
German companies in the 50's and the 60's. My favorites have been the Zenith
"Long Distance" AM/FM models of the period. Since the demise of the tube
receivers however, the emphasis in the market place has shifted away from RF
performance in favor of such things as stereo, portability, cassette
recorders and especially CHEAPNESS.

This has made enthusiasts like myself and others look for what the market
had to offer using solid state components. The closest thing one could find
in the 70's was a Panasonic. They were offering surprisingly good small
radios at a reasonable price. I do enjoy those but even the Tech Series
Panasonics emphasized other than straight AM/FM performance. Sony and Sharp
also had some fairly impressive small radios. The best of these radios did
utilize state of the art technology in their IF filters and such but still
did not employ basic receiver techniques such as separate oscillator and
mixer and an RF stage.

Finally, in 1979, GE of all companies, announced the first Superadio (model
7-2880). The idea of such a radio which boasted tuned RF stages on AM and
FM, a ceramic FM IF filter, 4 stages of AM IF tuned circuits, 6" speaker and
a 200 mm ferrite loopstick antenna was very intriguing. Knowing what GE had
offered previously and how they could not hold a candle to Panasonic did
make me skeptical. Nonetheless, when I tried one in a department store I was
able to receive numerous FM stations with the antenna down. Maybe it really
is good, I thought. Needless to say I acquired one. My wife surprised me
with it on my birthday in 1981. We were living in Easton, Pennsylvania at
the time were there are FM's at 95.1 and 96.1 MHz--a selectivity problem for
anything in between and an intermodulation problem for 94.1 and 97.1 MHz.
The radio pulled in WFLN-FM from Philadelphia @ 95.7 MHz with the antenna
down and WPLJ, 95.5 MHz from New York with the antenna properly positioned.

Yeah, OK, but can it do AM. Yes it can; its sensitivity handly blew away the
Norelco portable I had been using as a benchmark. The DAYTIME dial had few
gaps. The lowest dead frequency was 640 KHz.

I knew things were different now! I joined the small army of Superadio
enthusiasts to spread the word that there was finally a decent new radio for
AM/FM reception. It listed for $79.95. No, it doesn't play tapes and it
isn't stereo but no other portable you could find could even touch it for RF
performance.

In 1982 GE introduced a new model, the Superadio+ (model 7-2882_). This one
boasted many of the same performance features (RF stages, IF filters, 6"
speaker, 200 mm ferrite antenna). The difference was it was digital. Yes, A
PLL synthesized Superadio! This one was pricey. $139.95 retail. At first, I
passed. Apparently the Superadio+ didn't sell as well as the analog model
because after a mere year it was already available for the closeout price of
54.55. At this price my wife and I bought one at a Murphey Mart in West
Virginia.

Compared to the analog model, the performance is close but with some
sacrifices. There is a noticable increase of noise on AM when DXing requires
maximum sensitivity, most likely directly related to the synthesizer. FM
capture is good but sharply loses lock below a certain signal strength below
which the analog radio can still receive. There are eight presets on each
band, scanning features and a lighted display, but no direct frequency
access. There is a switch on the back to allow the radio to tune in 9 KHz
spacing for European use. The station memory requires 3 AAA batteries.

The all-time best seller among Superadios was the Superadio II (model
7-2885). This was an upgraded version of the first analog model. Obvious
changes included the addition of a piezo tweeter, more chrome and a flatter
speaker grille. Also depending on which revision letter follows the model
number on your particular radio, later earphone outputs accepted stereo
headphone plugs. Less obvious were the change in IF amplifier coupling and
some device changes inside. Also, later revisions used a different variable
capacitor but still 6-gang. I have tested many of these radios and compared
them against my own and another original Superadio.

Compared to the original, the AM IF gain on the SRII is increased, the FM
sensitivity is improved and selectivity is somewhat better on both bands. FM
capture on the original is somewhat more friendly however. The actual
tracking of sensitivity across the AM band seems to depend as much on the
individual unit as it does the model. For AM sensitivity measurements I
always use daytime signals because night skywave DXing brings questions of
masking, AVC variation, antenna polarization and selectivity into the
equation. My measurements use the built in ferrite for AM and the whip for
FM. No external antennas. As for the sound, the frequency response is quite
wide but the bandwidth available in the audio amplifier is in excess of what
should be expected from a 700 mW amplifier and much of the low frequency
information is wasted on a speaker that is inefficient at the low frequency
extreme of the amplifier. Using the bass and treble controls to contour the
sound helps a little.

Finally when Thomson bought GE and after about 10 years of Superadio IIs, a
new model was introduced, The Superadio III(model 7-2887_). This model is
more plastic-intensive than any other SR and is the most hollow, too. The
first production of this model, roughly through March of 1993, had serious
sensitivity problems. At that point I had only tested someone else's radio
but was so disappointed that I wrote to GE to tell them they had made a
mistake with the varactor tuning. The varactor tuning in the front end of
the receiver represents the most significant change in the model compared to
the SRII. Later I started to hear that the problems had been fixed and the
Superadio III really was good. So, my wife bought me a Superadio III for
Christmas in 1994. I made sure the date code was of the period that was not
affected by the earlier problems. Sure enough, this SRIII was much better
than the first one I tried. Compared to the SRII this one has a better
amplifier to speaker match and therefore gets better sound out of the same
700 mW amplifier chip. The AM (MW) now extends to 1700 KHz in hopes that the
congestion will someday be relieved in the rest of the band by reassigning
some stations up there. SRIII also has a wide bandwidth setting for extended
audio response. This does make local stations sound good but, of course,
fidelity sacrifices selectivity and sensitivity suffers quite a lot as well.
The narrowband setting has good selectivity, especially at the low frequency
end of the band. Based on several units tested, there is quite a bit more
internal noise on the AM with the SRIII than with either of the other two
analog models. There are a few new birdies too. This means that the most
demanding DXing needs will favor the older variable capacitor-tuned
Superadios for sensitivity. This sacrifice is undoubtedy the result of the
increased noise figure of the varactor-tuned front end as well as the
inability of all the varactors to track well over the required two and a
half octave tuning range of the AM band. The tracking error also contributes
to the absolutely abysmal dial calibration of the SRIII.

The FM on my SRIII is very nice. It can be hard to tune at the upper end
because the mechanism is sloshy but the selectivity is good and the intermod
and image rejection characteristics are better than with the SRII.

How do Superadios stack up to other high performance models? Compared to
older multiband models like the aforementioned Norelco and the
ultra-state-of the-art models like the Sony ICF-2010 (and even supposedly
the Bose Wave radio), it is clear that the emphasis on AM/FM radio
receptions makes the Superadios the best at what they do. Multiband radios
optimize the IF bandwidth for shortwave reception and can sacrifice BC
sideband information with selectivity merits that do nothing to improve AM
BC reception. Boom boxes usually have trashy radios because the emphasis is
on stereo, tapes, CD's etc. The one thing the Superadios still can't do
quite as well is the good old fashioned brute force sensitivity of a well
designed tube radio. The wide dynamic range and quiet, high impedance
amplifier stages in good tube radios has still not been matched even in the
world of shortwave reception. Solid state receivers require a higher degree
of complexity to accommodate dynamic characteristics that are inherent to
tubes. Of course, tubes are less reliable, power hungry and more expensive.

I like all good radios. Superadios provide the best reception available in
today's market and at a price that anyone can afford. I own all four of the
Superadio models and I know others who have even more.

T.David Zimmermann

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