Diamond D130NJ question

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picscan

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Okay, so I got a new antenna after my old beat up Radio Shack discone had only two radials left from about 25 years of use, I got the Diamond D130NJ and put it up today, very disappointed in the 800 P25 bands compared to the old antenna, every other frequency is awesome and a huge improvement, it is so noisy in the 800s even with Attenuation on the TRX-1, crackling and popping. What can I do to fix this, any pointers?
 

Ubbe

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Could it be that those troublesome channels are from simulcast systems and now the antenna are much better and receives several towers using the same frequency that now will interfere with each other? The old antenna was so bad that it only received one simulcast tower?

I assume you only have one digital scanner? What happens if you try and receive with the rubber antenna on the scanner? Is there no change at all when you engage the global attenuator when you monitor the 800MHz channels? Then you might need even more attenuation. What does the signal strengh says, does it change to a lower value when you use the attenuator? A variable 20dB attenuator should always be part of an external antenna installation to check for overload interferencies and simulcast problems as it will be a great help trying to figure out how to improve reception. If it is simulcast problem one solution could be to split out the 800Mhz range using a diplexer and then attenuate that signal and then combine it again with the rest of the frequency band before it goes to the scanner. You could use a 1/4 wave stub that are a short lenght of coax connected to a T connector that would attenuate the 800MHz band. It depends on what the reason are to the crackling and popping but it sounds as if the signal now are too strong.

/Ubbe
 

TailGator911

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Could it be that those troublesome channels are from simulcast systems and now the antenna are much better and receives several towers using the same frequency that now will interfere with each other?

Ubbe, this was my exact situation here with my simulcast system (Ohio MARCS P251) I put up the Diamond D130NJ discone and reception was remarkable except for my local P25. LSM was an even worse issue, just sounded like bad intermod and ducks quacking. I had it before, minimally, but the D130NJ made it worse. It seemed to be over-receiving. So, I invested in a directional yagi and pointed it directly at my desired site and the problem disappeared. Don't get me wrong, I still had lsm, but I followed my local system with 3 digital scanners off of the yagi thru a Stridsberg 4-port and had 2 scanners (BC536HP & WS-1065) scanning in opposite directions (one ascending, one descending) and a TRX-1 thrown in there for good measure. It worked well, and I had minimal lsm issues and was hearing almost everything. Now I have both the SDS100, and the SDS200 and lsm is not an issue at all. The Diamond D130NJ was definitely the culprit. Just too much. Great antenna!

JD
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picscan

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Thanks, it's weird because when I had the rubber ducky they seemed to come in with less noise. When I turn attenuate on it gets quieter with the discone but when using the rubber ducky with attenuate on it has more noise.
 

prcguy

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If you turn on attenuation and reception gets quieter (or better), that usually means the receiver is overloading and creating internal IMD, which can raise the receiver noise floor and interfere with or cover up some signals. The IMD is not necessarily a product of the signals you want to receive and could be very strong signals and usually more than one within the same band or in another band. The attenuation is globally reducing signal levels at all frequencies into the receiver and reducing them to a level where IMD is less likely.

Thanks, it's weird because when I had the rubber ducky they seemed to come in with less noise. When I turn attenuate on it gets quieter with the discone but when using the rubber ducky with attenuate on it has more noise.
 

BC_Scan

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I would be looking at the 25 year old coax, if you had to change antenna, you should also change coax, (unless done so allready) minimum RG-6 is acceptable, other coaxes are better. I have numerous discones in use all with good quality coax and end connectors. I have no issue with any 700 or 800 mhz freqs.
I am assuming you have the old coax still in place?
 

picscan

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I'm using newer RG-8 that is probably less than 6-7 years old. While I was waiting for my new antenna to arrive I was using a rubber ducky on my coax up on the mast and it worked way better than this. As a I said before, the other frequencies are great!
 
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Ubbe

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Judging from your description you have overload or simulcast problems in the 800MHz range and need to attenuate only that frequency range.

If you could find a frequency that you are sure isn't part of a simulcast system and still have problems with that frequency, then the whole 800Mhz needs attenuation, or if you can find the offending frequency/frequencies that are the source for overload you could possible filter them out.

But if it is only a simulcast problem and other frequencies in the 800MHz range works fine then you probably need to filter out the 800MHz range from the discone and use a directional antenna for that range, or get a scanner that handles simulcast problems like SDS100/200 and TRX100/200. Put a filter in the coax to the discone and connect another coax in parallell to the scanner with a suitable 800MHz directional antenna.
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/Ubbe
 

picscan

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Yes, it's the simulcast system, I'm using the TRX-1 and have found that a properly tuned paper clip works better than the discone.:cool:
 
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