help with unID on 760? and a couple other things.


Hi all...

I was listening to one of my local blowtorch stations, 760 KFMB, a 50kW directional station about 7 miles north/northwest of me. (My PL-380 caps at 63dBu RSSI on 760, and on the TP frequencies 747 and 774 (I've never heard anything on those yet), the "noise floor" / elevated RSSI, due to desensitization, is around 41-43dBu.)

Anyway, I was tuned slightly off channel, 756kHz, to coax out a bit more wideband audio, and I heard something else under the local, while holding my radio so that KFMB's signal wasn't quite as strong. I recorded about 25 minutes of me trying to receive the other signal, which consisted of periodically changing the bandwidth, occasionally tuning to 750 to check to see if it was that (I originally was in 6kHz mode), etc. I even briefly thought I was getting a TP or TA on 756, but I wanted to be sure. Eventually, though, I was able to narrow it down to it definitely being on 760, as if I remember correctly I had my BW down to 1 or 2 kHz, tuned to 760, and was still hearing the station periodically. Even so, I had extreme difficulty hanging onto the signal, partially because I had trouble keeping KFMB properly nulled, and because it was so weak under KFMB that most of the time I basically could only hear it during the split second moments when KFMB wasn't modulating, either between words, syllables, different speakers, etc.

BTW, the selective distorted fading (and other fading) isn't necessarily KFMB's signal fading, it's me trying to find and hold that sweet spot to get the best null of KFMB. If I just move the radio a couple degrees, tilt, rotate, etc in any direction, it makes the difference between a 15-18dBu signal on 760, and a 63dBu signal. (I basically had to hold the radio so the antenna was about 10-15° or so off from vertical, with the "top" of the internal antenna leaning toward the transmitter site.) Due to KFMB's strong signal, and the fact that there was an extremely small "sweet spot" to null KFMB, I was unable to "direction find" the other station. KFMB's 50kW transmitter is about 7.3 miles away at 321°, and according to the FCC their groundwave F/S @ 1km toward me is about 1813.92mV/m theoretical, or 1995.00mV/m augmented. According to ZipSignal, their F/S near my location is 301.12mV/m for 91941, and 219.74mV/m for 92020.

Anyway... one big hint came about 19 or 20 minutes into the recording, when I heard the Mexican National Anthem. This was at about 11:00pm, so I suspect (if my assumption is correct that they play the song at midnight on their stations) it's a Mexican XE- station in the central time zone.

This was done with my barefoot PL-380. Would anyone have any idea what station that is? Also, considering KFMB's strong signal, anyone have any tips on barefoot reception of TPs and TAs on 738, 747, 756, 765, 774, 783 from this location?

I am still keeping my eyes open for a pocket-size radio with the front-end selectivity I'm looking for. If possible, I'd like to be able to hear a 15,00 station (assuming the noise floor was low enough so that a 15,25 reading would be possible) that's 10khz away from a non-IBOC blowtorch that's strong enough to drive speakers to fill an average living room with about 60-70dB level, when hooked up to a crystal set WITHOUT an antenna. It seems that my PL-380 can't quite do that, though, unfortunately, not to mention it won't go in my pocket very well, which was the original purpose of getting it (I was trying to replace my Panasonic RQ-SW20 radio / tape player, which was a bit too bulky to go in there.)

Also, earlier this month, I thought I was hearing something on 1116kHz sometime between 3 and 5 one morning. Unfortunately, although I recorded it, in my brief searching the last couple minutes I can't remember which recording it is, and I can't find the notes I typed at the time referencing it. If I can find it, though, I may upload and post it, and see about getting help figuring out what it probably was.
I have, though, been doing various observations and comparisons with my PL-380, Panasonic RQ-SW20 (which has horrible back-end selectivity, but just about wipes the floor with the PL-380 in front-end selectivity), and a 1960s-vintage Zenith portable AM radio, which has a separate tuned front end circuit or two in front of the first IF mixer stage. I've done some experiments near transmitter sites, as well as at some distance away from town. I hope to be able to figure out a way to write up some kind of report on my findings sometime, complete with links to example recordings I made, but I don't know when that will happen, yet.

Also, I've noticed differing reports of sensitivity (compared to other radios) from some PL-380 owners. I've gotten to wondering... how close to local blowtorch stations are you all, and what is the RSSI reading on-channel, or in some cases, off-channel? The lowest noise floor possible, according to my observations, is such that you can have a signal with a 25dB SNR, with a RSSI of 15dBu. At the other extreme, near a very strong station, the RSSI may be 50dBu, with every signal below that registering 0dB SNR, across several channels or more. For example, at my grandparents' house in San Gabriel, CA, several stations in the 1200 to 1500kHz range or so are almost unreadable on my PL-380, due to a 23kW station on 1300 and a 50kW station on 1430 about 1/3 mile away, even though I was within radio-locator's predicted 2mV/m contour. On the other hand, when I did my Campo experiment somewhat recently, I was able to hear XEPRS-1090 with a better (although still weak) signal than the aforementioned almost-unreadables. (The strongest barefoot signal there was XEKT-1390, reading about 41,25 on the barefoot PL-380, and was the only signal that gave me a 63,25 reading with the Select-A-Tenna. The next weaker one was XESDD-1030, indicating 34,25 barefoot or 56,25 with the SAT.) This was even though I was something like 3 times farther than the predicted 0.5mV/m contour, or 2 times farther than where I would guess the 0.15mV/m contour would be. (XEPRS uses the nighttime pattern 24/7.) So, in a nutshell, it seems that the PL-380 seems more sensitive in rural areas, or areas without much of a strong signal, than in urban areas with lots of RF flying around.

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