P25 reception problem

[keithbias1]

Can anyone help with this? I have a home patrol 2 that I connected to a diskcone antenna. I live in a rural area and am wanting to monitor 3 different P25 counties. Each has their own tower. This is why i picked the diskcone. It seemed to be working pretty well until today. I noticed that i was not getting any of the trunking traffic but was able to pick up VHF with no problems at all. Some from quite a distance away. We have been having a lot of rain and wind in my area. I turned on my little portable with a rubber ducky anteana and was able to pick up some of the p25 traffic. Could the weather just shut down my reception that quickly or is there a problem with the antena. LIke i said i can recive VHF with no problems.

Thanks!!

 

[tvengr]

Did you seal the connectors? You can wrap them with electrical tape. Water in the connectors or coax can cause receive problems.

 

[keithbias1]

ya it is taped i guess water could be getting in. I just don't know if that is the best antenna. i thought about a directional but with having sites that are South, West, and North. kind of hard to do.

 

[bob550]

The discone is best for your monitoring situation. For every exterior connection, consider the use of coax seal. It's a thin rolled layer of putty-like weatherproof material that you wrap around each connection and press into place. I'm sure there's lots of weatherproofing suggestions in the Antenna forum. Does your coax lead have factory installed connectors, or are they DIY?

 

[keithbias1]

Factory on both ends. Then the diskcone sets on top of a pipe and the coax feeds down in the pipe and down the side of the house.

 

[doctordialtone]

IT'S Discone - D-I-S-C-O-N-E

Discone antenna - Wikipedia

en.wikipedia.org

 

[keithbias1]

IT'S Discone - D-I-S-C-O-N-E

Discone antenna - Wikipedia

en.wikipedia.org

sorry I didn’t spell that correctly

 

[radio3353]

IT'S Discone - D-I-S-C-O-N-E

Discone antenna - Wikipedia

en.wikipedia.org

Be careful...I have been warned by moderators more than once that being a grammar cop is frowned upon here. No room for education.

 

[bob550]

So you have the coax connected to the antenna on one end and the scanner on the other? Well, if the connection at the antenna is the only external one, that should be fairly well protected being inside the antenna mount.

 

[keithbias1]

That’s why I was thinking some kind of a nick in cable. I don’t know what else

 

[tvengr]

What type of coax are you using and how long is the run?

 

[keithbias1]

What type of coax are you using and how long is the run?

I have 100 foot of rg8 50 Ohm

 

[tvengr]

You can have a pretty significant signal loss with a run that long at 800 MHz compared to 150 MHz. The higher the frequency, the more the loss. Depending on the type of RG8, at 800 MHz with a 100' run and a 100 watt transmitter, you may have only about 25 watts reach the antenna. With the attenuation due to moisture in the air, you could completely lose a marginal 800 MHz signal while VHF and UHF will not be affected as much. You can use a preamp at the antenna to overcome the loss in the coax. If the antenna isn't very high, with a run that long you could be losing more that you gain with the discone.

 

[devicelab]

Or more simply that the trunking control channel changed to an alternate and your programming is off.

 

[keithbias1]

Would it be better if I cut it down to 50 foot?

 

[devicelab]

Would it be better if I cut it down to 50 foot?

If it was working before then this isn't your problem. Looking at the RR database I see a lot of SAFE-T sites w/o any alternate control channels. If a site switches to an alternate then no more trunk traffic for you.

 

[N8IAA]

This is why you put all frequencies in per site. It used to be that the older scanners needed space for TGID's and conventional frequencies.. Now, it's better because there is more space.

What devicelab posted is true. Modern systems change their control channels. Some are set up to roll them automatically. I stopped using just CC's a long time ago. Try it and see if it works.

 

[tvengr]

Would it be better if I cut it down to 50 foot?

If you have an extra 50' that is not needed, by all means shorten the cable or replace it with a 50' cable. Always use the shortest cable length possible to minimize loss. Raising the antenna height will almost always result in more signal than you lose in the additional cable length. Replacing the RG8 with LMR400 cable would reduce loss even more. If you have a long horizontal cable run to reach the antenna, consider moving the scanner closer to the antenna or moving the antenna closer to the scanner to shorten the cable length.