Re: July 2010 Oregon Beach Ultralight DXpedition Report


Mike Mayer <mwmayer@...>
 

All,

 

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:

 

http://en.wikipedia.org/wiki/Project_triangle

 

 

==========================================================
Mike Mayer
mwmayer@...


From: ultralightdx@... [mailto:ultralightdx@...] On Behalf Of D1028Gary@...
Sent: Wednesday, August 04, 2010 2:24 PM
To: ultralightdx@...
Subject: Re: [ultralightdx] Re: July 2010 Oregon Beach Ultralight DXpedition Report

 

 

Hello Tony and Stephen,

 

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.

 

73 and Good Luck,

Gary DeBock (in Puyallup, WA)                

 

 

 

In a message dated 8/4/2010 8:08:30 A.M. Pacific Daylight Time, germanotta.tony@gmail.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 some conditions. 

 

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 well.

 

 

 

On Aug 4, 2010, at 12:57 AM, Stephen wrote:



 

So are 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 lot.
And, for "international", for purposes of this post, I'm not including Mexico - 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 ultralightdx@yahoogroups.com, D1028Gary@... wrote:
>
> Hi Richard,
>
> Yes, I also wish you could have been in Oregon to enjoy the wild DXing
> fun-- chasing AM stations in Australia, New Zealand and the Pacific (from the
> west coast) is about the only way to have much AM-DXing fun in the middle of
> 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 DX at
> the same signal levels as the 7.5" loopstick PL-380, but with more domestic
> 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 7.5"
> loopstick PL-360 should be a fun radio for domestic DXing, where the selectivity
> 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:
>
>
>
>
> Gary:
>
> 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 have
> performed.
>
> Richard.
>
> Richard Allen
> 3622'51N / 9726'35"W
>

 

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