Exact time nonclearchannel stations power down?

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beamin

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I have an AM station up the street from me and sunset gives the best results for me on SW.

Whats the exact time they power down? Is it based of one of the sun setting times? Like civil twilight?

The 30 minutes after sun down is the sweet spot and I dont want to miss it! :)
 

toastycookies

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ka3jjz

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You would be better off buying a filter for the AM band that would your obvious issues with overloading. What is the frequency your station up the street operates on?

There are many such filters, but the ones by Par Electronics are perhaps the best known...Mike
 

Boombox

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Depending on how close "up the street" means, you might try shortening the whip antenna a little, or backing off on the RF gain, and see if that helps.

If nothing like that works, bandstop / bandpass filters like the ones suggested would do the trick, especially if your radio has an external antenna jack.
 

WA8ZTZ

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This can get a little bit complicated considering factors such as average monthly local sunset, critical hours, post sunset authorization (PSSA). (There is also a similar set of circumstances at sunrise).

These factors are different for every station so without knowing the call letters of the station you are referring to there is no way to say for sure what time they sign off, power down, or change pattern.

Your best option would be to call the station.
 

ka3jjz

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While a filter would help (especially if you have a desktop or SDR), if you're that close to the station, you might have RF blasting right through the (usually plastic) case, being coupled via your power connection, and a host of many other possibilities. Filters generally won't work well with portables for just these reasons.

Good Luck...Mike
 

beamin

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I have an SDRPlay and a bitx40 7Mhz Ham radio.
Antenna is a 68' foot long wire: horizontaly 20 feet off the ground from a 2nd story window then tied to a tree. On the house end it ties into a lead from a 3' foot copper pipe ground rod directly below the window. The two wires tie into a torroidial matching transformer then 20' long coax into the house where the radio is. The bitx picks up the station regardless of what ever frequency its tuned to with consistent signal strength no matter what frequency.
I primarily use the SDR for 1-30mhz.

Its a 50,000 watt AM broadcast station 2 miles from me.

On the SDR the station seems to come in on harmonic frequencies as well as other stations/sources of signal. Its like it modulates their carrier frequency. So everywhere there is a carrier I hear the am station on top of the actual source I'm listening to. Not as bad at night, because I think its 2500 watts at night.
 
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WA8ZTZ

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Sounds like a case of cross modulation. However, being that close to a 50kw flamethrower, some passive intermod and even audio rectification is possible.

You need to do some research on these. Unfortunately, you may never fully solve the problem.

My hunch is that torroid is part of the problem.
 

ka3jjz

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Here's a simple experiment that you can do that requires absolutely no special equipment. Take the antennas and grounds off the radios, and see if you can still hear that flamethrower, especially away from its nominal frequency. If you can (and I suspect that you will - I had a similar issue years ago), then you must find and resolve (if you can) the source of the RF coming in. This is the tough part - there are so many possible sources of reradiation that it will no doubt be a lot of work to nail them all. I've even heard of rust between joints or nails on aluminum gutters becoming crude diodes and rectifying a MW signal. If you should get this nailed down, then- and only then- should you consider a filter on your antenna.

I ended up putting toroids and wrap around transformers on every lead to and from my receivers (including speakers), a power line filter on every cable, and even then I didn't get rid of it all (I was living in an apartment, and had no way to address outdoor issues). This was a good 15-20 years ago. What a mess! I even had to put a transformer on my phone line because it was coming through that, too (Barbara Streisand and Mel Torme 24X7 surely a nightmare on Elm street, hi)

Mike
 

WA8ZTZ

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Here are some other experiments you can try:


Eliminate the toroid.

If possible, route the antenna such that the end is pointed directly at the broadcast station.

Get a passive preselector.

Take notes as you go about this so that you can compare results.
 

ka3jjz

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While there are a few schematics out there for a passive preselector, construction is technically challenging in an environment such as the OP's- the slightest sloppy solder joint or poor bonding could potentially cause trouble down the line.

There's only 1 commercially made one that I know of - (actually there's 2 - one with a T/R relay, and one without)...

MFJ Enterprises Inc.

The 1046 doesn't have the T/R relay

This assumes you have 'cleaned up' your environment as much as possible, the reasons for which I mentioned earlier.

Mike
 

ka3jjz

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Keep in mind that any unshielded wiring can and probably will active as an unintended antenna for that station. If it's unshielded, assume it can conduct and act accordingly. Coax cables may need to look at any potential common mode issues. You may need a 1:1 unun to isolate it. There are numerous schematics on the web for these, and there are a few commercial units, too.

Mike
 

WA8ZTZ

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This assumes you have 'cleaned up' your environment as much as possible, the reasons for which I mentioned earlier.

Mike
Right, don't spend money on a preselector until you have tried to clean things up as much as possible and have experimented with the antenna.

Maybe a loop antenna would be helpful.

Another thing to consider would be a phasing box such as a MFJ 1026, but again try some of the other things first before throwing money at this problem.

Given that you are only 2 mi from the station, you could easily be seeing several hundred mV/m signal.
Therefore, there may not be an easy totally satisfactory fix.
 

mbott

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beamin

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Keep in mind that any unshielded wiring can and probably will active as an unintended antenna for that station. If it's unshielded, assume it can conduct and act accordingly. Coax cables may need to look at any potential common mode issues. You may need a 1:1 unun to isolate it. There are numerous schematics on the web for these, and there are a few commercial units, too.

Mike
Would it be beneficial to run coax to the ground rod? The ground wire from the copper pipe is about 20 feet long. Do I just leave the shield disconnected of the coax or do I ground that too?
 

ka3jjz

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At 20 foot long, I'd say it's time to rethink how that ground is set up. I can see that actually acting as its own part of the antenna on the higher HF frequencies in certain cases (like say using an inverted L or random wire as an antenna.). In addition you might be setting yourself up to be more prone to lightning strikes. Proper bonding at all points will help reduce the chances, although with lightning, you should assume that's nothing absolute..

Putting in a good RF ground is not the same as a good electrical ground to prevent shocks. While they can be related, it's a fairly difficult topic to master. I would definitely think about getting an electrician before going any further...Mike
 
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