18 November 2006

mediumwave images on the sw7600gr

I love my Sony ICF SW7600GR. I haven't used it much recently, because it is one of the older radios in my collection and there are newer radios that I am trying to get to know. But it is a really great product.

Another Sony radio that I own, the $10 ICF S10MK2, is exceptional. Early this year, I put alkaline batteries in it, and they are still going after more than 300 hours of use. It has surprising audio quality given its low price.

My experience has been that Sony portable radios are built well, sound great, and perform exceptionally.

My SW7600GR frustrates me in one area: mediumwave images within the longwave frequencies. Tuning to a particular frequency in the 150-500 khz range, I may hear a mediumwave station that is actually 910 khz above the tuned frequency. 190 khz and 350 khz are used up by local mediumwave broadcasters, while several other frequencies have fainter mediumwave images.

This radio uses dual conversion for AM reception, so I am not sure why this image problem exists within this frequency range. Is it possible that the longwave frequency range uses single conversion?

The only signal I have picked up near the longwave range is the airport beacon in Montague, California on 404 khz. But the mediumwave images I am hearing dissuade me from investigating longwave further.


Anonymous said...

Besides battery life, what do you like about the ICF S10MK2? I like my 7600GR too, but on FM it lacks enough selectivity for me. The E5 is much better in this regard. Is FM any better on the ICF S10MK2?

Dean W. Armstrong said...

910 is 2 x 455kHz, which does sound like a single conversion. Could the AM broadcasters be getting into the final mixer directly, without going through the other stages? I have this problem as well with the Degen 1103.

My experience with longwave is that it is location specific--my apartment (in Chicago) is the best place for it I've tried; on a campus roof it's a mess; and in Las Vegas there is nothing on LW save LORAN-C at 100kHz. Whereas in Chicago I pick up at least 4 or 5 beacons (see here for those).

weatherall said...

To Anonymous:
I haven't spent much time evaluating the FM selectivity on my S10 MK2 yet. A quick scan through the FM dial suggested to me that it was better than the WRX911. I'll try to find the time to do some more in-depth comparison. This is an interesting area for FM reception; some of the stations above 100 mhz have images on cheaper FM radios that I own.

weatherall said...

That's an interesting thought. I want to investigate that further when I have the time.

Thanks for the link to your longwave findings!

Anonymous said...

People always tend to expect perfect image rejection from dual conversion sets - in fact, it's limited by the filter on the first IF and leakage around it. The Sonys are a particularly good example with less than 40 dB of image rejection. Something employing frontend tracking (rather than a wideband frontend) on MW/LW would have no problem improving this by 20+ dB, all the more the lower the received frequency is. Try an analog set with MW/LW coverage and decently large antenna next to the 7600GR as a "booster".