LOOKING FOR FM RCVR FOR EAS

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RGORJANCE
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LOOKING FOR FM RCVR FOR EAS

Post by RGORJANCE »

Got an issue with severe front end overload of modern rcvrs due to being about 100 feet from our class A FM tower. Anyone got a brand name/model number for a rcvr that actually will not overload. Or perhaps an inexpensive tuneable notch filter that will help. Our old one just died and the new one we bought won't hear anything else but us. It is pretty lame. The other FM rcvr, which is real old still works fine for the LP-1 we monitor.

I am also not overlooking the possibility of RF slamming right thru the new rcvr box itself. Any thoughts/ideas will be appreciated.

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Re: LOOKING FOR FM RCVR FOR EAS

Post by Deep Thought »

You could try the old-school quarter-wave stub trap cut to your class-A frequency if it is not too close to the desired receive frequency. I've had quite good luck getting a 15-20 dB notch which should be enough. If it is a shielding problem that's easy enough to test by wrapping the thing with foil. You don't even need to ground it.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com
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Re: LOOKING FOR FM RCVR FOR EAS

Post by RGORJANCE »

Oh Poo!!! I never thought about that trick. I will definitely give that a shot. Musta been a senior moment. I was overthinking it.
Thanks Deep!
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Re: LOOKING FOR FM RCVR FOR EAS

Post by DaveSt »

In this situation it would good to have a spectrum analyser available so that you can see the unwanted level and hopefully the wanted signal too. That way you can work out how much filtering you need and whether you can add a pad (attenuator) at the receiver input. If you do not have a spectrum analyser, try a 10dB or 20db pad.

If you have a reasonable receiver you should aim to get the sum of the unwanteds to be below -10dBm at the receiver input and the wanted to be significantly better than -60dBm.
Last edited by DaveSt on Mon Oct 04, 2021 12:25 pm, edited 2 times in total.
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Re: LOOKING FOR FM RCVR FOR EAS

Post by TPT »

Maybe just lucky, or monitoring assignments work out--but I've had good luck using old "name brand" hi-fi tuners off e-bay. My one site has 17 kw ERP 160' above the studio. Granted, the building was built with chicken wire (grounded) behind the sheet rock but I still need outside antennas.

Have a Carver tuner on my monitor feed for the class A run out of the same location--that station is 25 miles away. One EAS monitored station is only 15 miles away, a Class B--I just use a radio shack tuner for that one. But another is a class B 45 miles away, I use a 70's vintage Kenwood for that one. A third station I monitor is 50 miles away, another class B, using a Harman-Kardon tuner.

My B-1 is on 93.9; our Class A is on 92.3 picked up on the Carver. Radio Shack Auvio tuner: 95.1; Kenwood: 98.7, Harman-Kardon: 91.3.

If you can find tuners with "slide rule" dials, then you don't need to put them on battery back-up. Also, the older ones are easy to work on--I usually replace the filter caps.
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Re: LOOKING FOR FM RCVR FOR EAS

Post by grich »

DaveSt wrote: Mon Oct 04, 2021 10:34 am In this situation it would good to have a spectrum analyser available so that you can see the unwanted level and hopefully the wanted signal too. That way you can work out how much filtering you need and whether you can add a pad (attenuator) at the receiver input. If you do not have a spectrum analyser, try a 10dB or 20db pad.

If you have a reasonable receiver you should aim to the sum of the unwanteds to be below -10dBm at the receiver input sand the wanted to be significantly better than -60dBm.
We just replaced a failed DASDEC with another, and the internal tuner was having issues with AM 1700 kHz bleeding into anything we tuned it to. We are using a shielded loop for an antenna, but the 1700 tower is in the same azimuth as the desired tower. The desired tower just happens to be 50 kW blowtorch WHO at 1040 kHz, so signal strength is no issue. A 10db pad was enough to cure the problem.

BTW, the old DASDEC failed because the power connector on the SSD burned, hot enough to melt two nearby audio cables routing audio from the receiver board to the motherboard sound chip.
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Re: LOOKING FOR FM RCVR FOR EAS

Post by RGORJANCE »

Thanks, guys! Got a couple avenues to explore on this now. Hoping that this turns out to be easy.
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