Re: Question about ultralight and loops for MW


pianoplayer88key
 

He also asked about the issue of living near high powered MW stations. I'll share a little of my experience. In rural areas (or other areas that don't have a strong signal nearby), I've found that the noise floor, as indicated on the radio, is 15dBu RSSI. I've seen stations that had a listenable signal at 15dBu RSSI, 18dB SNR or so. Yesterday I saw a 17dBu RSSI, 22dB SNR signal while my radio was inside a car (which attenuated the strong signals).
However.... when there are strong signals, it seems to desensitize the radio some. This is manifested by elevated RSSI readings across much of the band. For example, I live about 9 miles from a 50kW daytimer (2.9kW night) on 1170, 6 miles from a 10kW on 1130, and 7 miles from a 50kW nighttimer (5kW daytime) on 760. Except for the extreme edges of the band, the RSSI reading across most of the band on my Tecsun PL-380 is about 30dBu on otherwise "empty" channels. Within about 20-30kHz or so of the strong stations I mentioned, the RSSI will hit 39dBu or 41dBu, sometimes 43dBu between channels.
Also, my grandparents in San Gabriel, CA, live about 0.3 mi from a 23kW on 1300 and a 50kW on 1430, and about 5 mi from a 50kW IBOC on 1110. When I last visited them a few months ago, the RSSI throughout most of the band above about 1000 kHz or so was 49 to 50dBu on the "blank" channels.
Also, I experimented (and posted the results in an earlier post) with taking an older radio I have, generating the local oscillator carrier, and putting my PL-380 near it. When the other radio was on, the PL-380 would be showing 50dBu about +/- 150kHz from the frequency the other radio's LO was on. So, with the other radio turned off, and being in a car to partially shield the strong signals (so I wouldn't get the aforementioned 41dBu RSSI on a few frequencies, or 30dBu across the band; it was 15dBu across most of the band, maybe 20dBu near the strong stations), I would find a few stations to compare. Basically, with the other interference/carrier turned off, I might be able to hear a station that was about 35 to 40 dBu or so quite well. However, when turning that other radio (and its local oscillator) on, the target station went to fairly clear (with a little static) to virtually undetectable, if I remember correctly.
Also, I went near the transmitter site of a semi-local on 1450, and compared my PL-380 with a radio I have, the Panasonic RQ-SW20, which has selectivity comparable to the Sony SRF-M37 series radios. I also posted links to mp3 recordings of some of those comparisons, which I will not repeat here, except that there were several stations that, in spite of the horrible selectivity on the RQ-SW20 (1450 was being heard across several hundred kHz on frequencies where there weren't other stations on the dial), could be heard fairly well on the SW20, but were either extremely faint or just not there at all on the PL-380. Normally, the PL-380 is at least several dB more sensitive than the SW20, at least when it's not swamped by strong signals.

Now... Gary... what's your experience? I understand you can get perfectly clean audio from a distant station on 1460 (for which you're almost on radio-locator's fringe contour if I remember correctly), while you're about 3 miles from a local on 1450. I don't think my PL-380 would have a chance at that... not to mention that even in the 1kHz bandwidth mode, I often get somewhat noticeable splatter 10kHz away from 10kW stations about 30 miles away or so. (Also I think you've mentioned that my own PL-380 is probably defective. Any ideas on how to get it replaced? I would prefer not to spend the money on buying another one, unless I can get a vertically-oriented radio with multiple bandwidths and a good built-in Amidon-61 loopstick that doesn't protrude above the cabinet. The PL-360 won't cut it for me - single bandwidth, I'm afraid that the antenna will break off when I put the radio in my pants pocket where it will be primarily used (and where I was originally hoping to use the PL-380 but it won't fit there so by my definition it's not a ULR (although it still is by the committee's definition))... and I would prefer one a little wider (max of 4 inches IF the cabinet is no more than an inch thick, preferably 3.5" wide or less) so it can have a better loopstick in it, but shorter to keep its size under control.

So... Gary... when do you think you'll have the opportunity to check the RSSI near your strong signals? I would think your PL-380 shows 63dBu at 1450kHz (mine is capped at 63dBu, and it shows that on 5kW stations 8-10 miles away)... and based on how good the selectivity is on your specific PL-380, it would show 15dBu on 1440 and maybe 1460, right? Or what does it read? (Mine would probably read upwards of 30-45dBu where you are, not 15dBu. :( )

--- In ultralightdx@..., D1028Gary@... wrote:

Hello Sarmento,

Many air core and ferrite core external loops give excellent performance
with the Tecsun PL-380 and PL-310 models, and make DXing a lot more fun.

Depending upon your DXing preferences, you can choose a transplanted
ferrite loop (like the 7.5" loopstick PL-380), an inductively coupled ferrite
loop (like the Q-stick) or a direct or inductively-coupled air core loop. All
of these antenna designs have performance tradeoffs, and no one design is
perfect for every situation.

Most DXers who wish to avoid "surgery" on the radio use air or ferrite core
loops with the inductive coupling system, which gives an excellent
performance boost (depending on the size of the loop) with an extra tuned circuit
to aid in selectivity. The directly-connected ferrite and air core loops
always require modification to the radio (and possibly the addition of other
external hard-wired components), but avoid the need for a separate tuning
step.

My own favorite for convenient DXpedition usage is the 3' portable PVC air
core loop, which is described in the photo article at
_http://www.mediafire.com/?hqyzzu1mvyt_ (http://www.mediafire.com/?hqyzzu1mvyt) . This tuned
passive loop provides a powerful inductive coupling boost for the barefoot
PL-380, can be assembled in 2 minutes, and will fit inside a packed compact
car trunk.

73 and Good DX,
Gary DeBock (in Puyallup, WA, USA)




In a message dated 7/6/2010 4:12:29 A.M. Pacific Daylight Time,
sarmento.campos@... writes:




Hi

After have seen info about these new DSP receivers (like PL310/380) :

_http://bbs.tecsun.com.cn/0002.asp?open=186695_
(http://bbs.tecsun.com.cn/0002.asp?open=186695)

I wonder if it would support loop antennas, like square air coil or even
ferrite loops.

If one issue to add : living near big power MW stations.

Have anyone tried MW dx in this conditions ?

Regards
Sarmento - Rio de Janeiro - Brazil

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