Thursday, May 19, 2011

More thoughts about KPAC noises

I posted my experiment on KPAC to the Yahoo Group FMTuners, and there has been a lively discussion.

Here's some bits of followup posts I made:

I had trouble finding the Kenwood manual too and was going from lousy memory. If reading at friends house was about 64dB, that means 69.2dB according to the table, not 70 as I reported previously FWIW. I think 85dBf is a bit low for the meter markings to top out, but IIRC you can also extrapolate about 20db higher than the last marking and it's still mostly OK. I think I was pushing 110dBf into it and it was still moving higher though beginning to compress somewhat. This was many years ago and I can't remember exactly. I know at some level I could produce with my ST-1000A the meter started to compress (or maybe the ST-1000A).

Yeah I should probably call the station pretty soon now. Prior to doing this test (which took ten years of procrastination to get around to and still might not have happened) I didn't think I had a very good case. I figured I was much farther from the transmitter (>30 miles not 21) and it was quite likely I had a reception problem.

And furthermore I never noticed the buzz before getting my Kenwood KT-6040 in March 2011, and I think the buzz is not caused by a legal subcarrier, more likely equipment fault like ground loop. The 6040 is said to have adequate subcarrier rejection for modern subcarriers, whereas many of my older tuners do not.

The swishing sound could be a subcarrier thing, I think, perhaps even the result of a fully legal subcarrier (though KPAC does not have HD, and there are no nearby stations with HD either). The KT-6040 (and also Pioneer F-26) eliminate it almost, but not quite, entirely at my home (65dBf), you have to put your ear right to the speaker to hear it with those tuners. I'm just now testing a Pioneer TX-9500II that may have serious problems, and you can't miss the swishing sound, and that is how it has been with many older tuners in the past. Only when you get to the modern era tuners* like Yamaha TX-1000 (or F-26 !) do you get performance not unlike the KT-6040 for which the swishing sound is only a problem for perfectionists like me and takes serious concentration to hear. Perhaps they have some subcarrier which is just slightly beyond specs, or maybe this is "spec" performance.

But with the quiet background of the Pioneer F-26, the buzz which I just started noticing recently is a huge annoyance, though probably average person with average tuner wouldn't notice. Plus, lacking high blend I can't eliminate it as easily as I could with KT-6040. That's what got me moving on this issue. Except for the buzz, I get the most beautiful sound.

Tube tuners like KM-60 also don't project much of the swishing sound. I think that is because they have lousy HF separation, or at least mine does. It's mainly a problem for early transistor tuners where they started pushing the HF separation up, but without having sophisticated MPX circuits or antibirdie filtering.


I don't think KPAC has RDS, though maybe I don't understand RDS. It does not
show any content or category information on my car stereo (2006 Prius with JBL
stereo upgrade) like other stations do. Just 88.3, last I checked.

I've always been suspicious, however, that they stick some non-standard
subcarrier to run or help manage their repeater station KTXI. And classical
radio stations in my experience have often done plain old SCA to make a few
extra bucks.

The funny swishing noises have been there as long as I've been in San Antonio,
1992, but most of these subcarriers existed then anyway if under different

Aren't the rules now for subcarriers pretty wide open? I though they can now
put out whatever they want within the 200kHz station bandwidth, as long as it
doesn't overlap the baseband and stereo modulations at 23-53kHz.

No comments:

Post a Comment