Business License Repeater Frequency Help

[Mattguy]

I just got an email from my coordinator for my vhf business license to monitor 5 frequencies that he has given me. 151.8650, 151.9550, 153.0200, 158.3850 and 159.7200. All clear on the 5 frequencies he has given me but I wanted to get some input on spacing. Would it be better to go 151.8650 and 159.7200? Or is closer better. This is for my repeater setup. Will be using duplexer. Thanks for any help.

 

[Thunderknight]

In a duplexer, further is better. Smaller, cheaper, less loss.
If you are going at a shared site, other users and intermod study results can dictate the best choice.

 

[Mattguy]

The site is at my own shop with tower about 50ft in the air. Running a GR1225, with CDM1250 mobiles, and CP200 hand helds. I just would assume the further apart the better for frequencies but wanted to get some opinions. I know uhf has uniform spacing. Thank you!

 

[sfd119]

One of the freqs should have an FB2 with the FCC. That should be your repeater output. Then you can decide the input...

 

[kayn1n32008]

If you want to run 5/8wave antemmas, you may want to use a pair that is closer together... also, on VHF you will be be ok with a 2 or 3MHz split. Going to 8MHz is pretty pointless.

 

[Mattguy]

I have a tram 1491 antenna. Andrews cable.

 

[Mattguy]

Which pair would you use?

 

[kayn1n32008]

I have a tram 1491 antenna. Andrews cable.

I mean for your mobiles... 1.5:1 VSWR bandwidth is pretty narrow.

 

[kayn1n32008]

Which pair would you use?

I would use 153.020/158.365, if you do not have a lot of cash to spend on a duplexer. If you can sink the cash into a duplexer good duplexer, I would go with 158.385/159.720

If you go with 151.865/159.720 you will have issues with antenna tuning for the mobiles, unless you use either 1/2wave or 1/4wave antennas.

For the mobiles, tune your antenna to the repeater input frequency.


Sent from my iPad using Tapatalk

 

[Mattguy]

I am monitoring 153.0200 and something is using this frequency. Nothing is being said, but it's sounds keyed up. No one has this frequency for my area, I wonder if it's an illegal use.

 

[sfd119]

Could just be interference.

 

[Mattguy]

Wouldn't that affect my repeater. I will be running a pl.

 

[rapidcharger]

Wouldn't that affect my repeater. I will be running a pl.

PL tones don't remove the interference. It just mutes anything from coming through the speaker. What are you hearing that on? A scanner or a radio? Voices or noises?

 

[Mattguy]

Its just like a radio keyed up with nothing being said.

 

[Mattguy]

I'm listening on my cdm1250. I programmed the 5 frequencies and have been driving around doing a zone scan on those.

 

[zz0468]

Its just like a radio keyed up with nothing being said.

Does it go away when you disconnect the antenna? If you're listening with a scanner, it could be a 'birdie', an internally generated signal. It could also be something very local, like a computer or cable modem or some such thing.

 

[Mattguy]

The only time I hear it is when I open squelch. I have a nmo mount on my truck with a browning pre tuned 152 antenna. I will unhook antenna tomorrow and see what happens.

 

[Mattguy]

I should clarify, a cdm1250 is a motorola 50 watt mobile.

 

[zz0468]

T...I just would assume the further apart the better for frequencies but wanted to get some opinions...

In general, that's true. But there are other factors to consider. Duplexers capable of close frequency spacing are more expensive than one designed for wide spacing, but if you can get a quieter pair that's close spaced, vs. several co-channel users on a wide spaced channel, the extra expense might be worth it.

I once maintained a public safety system on VHF that had 240 KHz spacing. It was, at the time, the closest spaced VHF repeater in the country, at least in the public safety world. It worked quite well, with quarter kilowatt transmitters, but the filtering on both transmitters and receivers cost a fortune and took up a lot of space.

So, it's a trade between economics, co-channel interference, and physical space available.

 

[zz0468]

The only time I hear it is when I open squelch. I have a nmo mount on my truck with a browning pre tuned 152 antenna. I will unhook antenna tomorrow and see what happens.

I wasn't paying close enough attention when you said you were listening on a CDM1250. Probably not a birdie. But there are plenty of other local sources of interference that it could be that won't be a factor. Tracking it down to see what it really is could end up getting quite involved.