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Just to add to the information here, it is
good to keep in mind that designing a radio is an exercise in making tradeoffs
and compromises. Any one who is an engineer has had to deal with it every day.
There is no perfect solution, only a compromise between competing and sometimes
contradictory requirements. There is even a Wikipedia page about how engineers
talk about the subject. It is the phrase Fast, Good, Cheap: pick any two:
From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of D1028Gary@...
Sent: Wednesday, August 04, 2010
Subject: Re: [ultralightdx] Re:
July 2010 Oregon Beach Ultralight DXpedition Report
Tony, that was a very profound and
thorough discussion of a DXer's options in dealing with RF overload issues
(certainly worthy of re-posting in our Ultralightdx file section in article
form, if you are so inclined).
Stephen, like Tony says, if you are
already having severe RF overload issues with your local pests, the last thing
you should be doing is trying to boost the sensitivity of your
ULR by going for larger loopsticks. Plastic-cabinet Ultralight radios
lack the extensive RF shielding used in expensive communications
receivers, which typically use coaxial antenna connectors and grounding
posts to minimize the household RF hash coming from computers, plasma
TV's, etc. Since we choose to use Ultralight radios anyway (despite this
limitation), it is up to us to find solutions to RF overload problems.
There is a very good reason why
DXpeditioners try to set up in isolated locations, far away from urban RF
pests, and household RF hash. The 9 kHz-split DX signals from overseas
are usually very weak in comparison to domestic pest stations, and serious
domestic splatter or spurious products would be a deal-breaker. For Ultralight
radio users, it is especially important to get away from these type of
problems, since our radios lack the internal shielding and overload
protection common in communications receivers. Frankly, Stephen, if you want
better DXing results from overseas, your best option would be to "get out
of Dodge," and head for an isolated ocean beach DXing location as far away
as possible from urban RF blowtorches. Then you can reasonably consider
mega-loopsticks, monster loops and/or beverages to boost up your
weak-signal AM sensitivity.
Keep in mind that there is no perfect
DXing location in California,
or in any other state. I lived in San Diego from
1974-1975 while in the Navy, and even with many of the stations signing
off at midnight, my impression was that the entire Southern
California area was an RF hash zoo. We all need to do the best we
can with the resources we have available, and my advice would be to just get
started, and do the best you can on the AM frequencies that you have open.
As long as you have reasonable expectations, you can still have plenty of DXing
fun in the fall season as conditions improve.
Gary DeBock (in Puyallup,
In a message dated 8/4/2010 8:08:30 A.M.
Pacific Daylight Time, email@example.com writes:
Stephen, you keep asking the same question
in different ways, but the answer can't change. If you are in an area where
your portable radio is being overwhelmed by RF splatter from other stations,
it's pretty much impossible to hear the, by definition, faint signals from DX
stations. It's like trying to DX under the noise of a bad fluorescent bulb. I
have one in a back room that just wipes out the entire band when I forget to
turn it off.
Can you build a preselector? Sure. What
will it do. Well, there are types that peak up just one narrow band of
frequencies. That helps sometimes, and others that block out either everything
above its designed frequency or everything below. And those can help sometimes
and some that just notch out one slice of the bandwidth. Again, it can help in
But if your area is buried by
off-frequency splatter, which seems to be the case from your various postings,
then none of those will help at all because the offending frequency will be on
the same frequency you are trying to DX. If you filter it out, your DX is also
blocked from the receiver. The FCC in recent years has become pretty lax on
keeping AM stations to their specs, I have discovered. There just aren't that
many folks like us out there who get offended by the local talk station bleeds
over 10KHz, since there is usually no other local station on the air there. And
the days of clear channel stations designed to cover wide sections of the
country are over. Those frequencies are now shared by several stations with national
coverage now something ceded to the internet, satellite radios or just not
deemed a national priority anymore.
You keep searching for more sensitivity
when your problem is probably too much signal already.
Changing out the internal ferrite won't
help if it makes the radio more sensitive in an area already over washed by RF.
What you might want to do is cut sensitivity some. That's easy on radio's with
a DX/Local switch that puts an attenuator between the antenna and the front
end. You can do that yourself on shortwave or FM with your radio, but the AM
circuit doesn't have that kind of outside input unless you go to the little one
with the external antenna jack. On that one, you could put a variable resistor,
or Pot, in line and use that to cut signal. There are better ways to do it,
with resistance boxes, if you find the rough method works. With your radio, the
antenna is always in line. So you can try reducing signal by putting the radio
in a grounded metal can, for instance, with just a small opening for RF to get
through. That might reduce the RF to below the point where it is overwhelming
the chip and causing it to do weird things by going what they call non-linear.
Before you do that, though, try to borrow a radio with an attenuator on
board and see if it does anything for you. Again, if the locals are
broadcasting over adjacent frequencies rather than your radio just being
overwhelmed and reproducing them on those frequencies, attenuation won't help.
It will just reduce both the DX and the local pest equally and the DX is going
to be the loser, since it is much, much weaker. If the attenuation helps, then
you know it's overload causing the majority of your problems. And you can build
your attenuating can.
Of course, you won't be able to fit that
in your pants pocket. Then again, DXing isn't something you do while taking a
walk. Moving a couple feet inside a house can make a ton of difference in DX
sometimes because of the way the radio waves are being reflected and blocked by
stuff in your walls an attic. That said, sometimes heading to the far
reaches of the back yard can improve things by getting away from near field RF
noise. Then again, you may just be moving closer to the neighbor with the bad
bulb, aquarium heater or touch lamp that causes all sorts of problems. The
first thing I would do is look for noise sources. Find a spot on the radio that
just crackles with noise and try to track down the source.
My plasma TV is a real nuisance when I
try to DX. Some computers are just noise generators. The solution, shut off the
problems when you start a session. One method that works is to turn off all the
circuit breakers in your house and then flick them on, individually, and listen
for the noise. When you find one or more that has problems, then you DF in the
areas those breakers serve. You will be surprised what kinds of things can
cause problems. The wall wart charger on a portable phone or cordless razor,
for instance. Light dimming switches are notorious. Microwave ovens or the digital
displays on appliances have been known to radiate noise if you're too close.
And remember, all of this can vary from
frequency to frequency. On some, the radio may just be overloaded. On others,
the local may be operating out of its assigned bandwidth. I'd do that kind of
work first before trying to gut the 380 and replace anything. You have to
identify the problem before you can engineer the solution, I've always found.
Good luck. And don't just give up the
radio. You might find a lot of fun taking it on summer vacation trips or
discover a world of DX if you and your family go camping. And it's still a
great SW and FM receiver and there's lots of DX fun available on those bands as
On Aug 4, 2010, at 12:57 AM, Stephen
there any tips, short of going to an alternate location, to try for
international DX with my PL-380 and Select-A-Tenna? I live in a fairly
RF-saturated environment, which doesn't help, and it's difficult, if not
impossible, for me to travel to other locations at this time. (If I had the
opportunity, I might want to try going to somewhere west of Santa Barbara, CA
(on the California coast) to try for some DX, but that doesn't look like it
will happen anytime in the near future.) For now, though, the maximum extent of
my "DXpedition trek" would extend to my back yard on the 1/2-acre
And, for "international", for purposes of this post, I'm not
- I can get several AM and FM stations 24/7, some of which peg the SNR meter,
and one AM pegs the RSSI meter in the daytime as well.
Or, should I resign myself to never doing any meaningful DX from here, and sell
my PL-380? I do remember Scott Willingham in a post last week or so mentioning
something about 3 ways to improve selectivity, one of which was to install
passive filtering in front of the DSP chip. Is doing something like that that
even remotely a possibility? And, while I'm at it (if I was to attempt
something like that), what about pulling the guts out of the PL-380 cabinet,
substituting a separate loopstick (would have to be no longer than 3 to 4
inches long and 1/2 inch thick, assuming it takes the entire width and almost
the entire thickness of the radio, as it will have to fit in my pants pocket
and 4" is the absolute maximum width that would reasonably go in there -
my PL-380 will go in there but it's awkward), and basically crafting my own
vertically-oriented ultralight based on the PL-380's guts, or would it not even
be considered in the "unlimited" category? :(
--- In firstname.lastname@example.org,
> Hi Richard,
> Yes, I also wish you could have been in Oregon
to enjoy the wild DXing
> fun-- chasing AM stations in Australia,
and the Pacific (from the
> west coast) is about the only way to have much AM-DXing fun in the middle
> summer. It's kind of like a head start on the Fall Season!
> The 7.5" loopstick PL-360 would have received all the South Pacific
> the same signal levels as the 7.5" loopstick PL-380, but with more
> splatter in some cases (because of the fixed 3 kHz DSP selectivity in the
> PL-360). This wouldn't have happened in all cases, though, like in
> receiving 891-5AN, which had no domestic splatter anywhere nearby. The
> loopstick PL-360 should be a fun radio for domestic DXing, where the
> requirements aren't as great as in 9 kHz-split DXing.
> 73, Gary
> In a message dated 8/3/2010 4:41:46 P.M. Pacific Daylight Time,
> richarda@... writes:
> Thanks for the report. I wish I could have been there to enjoy the DXing
> fun. It would have been nice to see how the PL-360/7.5" combo might
> Richard Allen
> 3622'51N / 9726'35"W