Quantar or Tait TB9100 for P25C?

[Cameron314]

IP link? We used to have some point to point radios that used a pair of RG-6 like that. Would sometimes find the same thing. I offered to make custom cables for them, but they weren't interested. Their attitude was "if it works, it works".

The old Cisco Aironet (or whatever) used two coax cables but those have been gone for years. Likely just two shielded outdoor Cat5/6 cables. No real loss with some extra.

 

[BMDaug]

Are you seeing a trucked site with combiner and receiver multicoupler antennas by chance?

They are trunked sites mostly. I know they use two folded dipole arrays, one for RX and one for TX. One of the administrators that helped build the network has breakfast with the ham club every week. It’s just the distance between antennas on the tower I’m not positive about. It’s hard to judge distance and scale on a tower for me sometimes. I’ll ask him about the antenna setup next meeting.

-B

 

[Cameron314]

They are trunked sites mostly. I know they use two folded dipole arrays, one for RX and one for TX. One of the administrators that helped build the network has breakfast with the ham club every week. It’s just the distance between antennas on the tower I’m not positive about. It’s hard to judge distance and scale on a tower for me sometimes. I’ll ask him about the antenna setup next meeting.

-B

So those aren't just two antennas with one going directly into the RX port and one going to the TX port of a repeater like it sounds like you are wanting to do. You just need to get a duplexer if you only have a single repeater.

 

[mmckenna]

The old Cisco Aironet (or whatever) used two coax cables but those have been gone for years. Likely just two shielded outdoor Cat5/6 cables. No real loss with some extra.

No, these were RG-6. I grabbed the reel of cable when they were going to throw it out. I used it to move a satellite internet dish at one of our remote sites. It was many years ago, however. I -do- know the difference between twisted pair and coaxial cable at this point in my career.

 

[BMDaug]

So those aren't just two antennas with one going directly into the RX port and one going to the TX port of a repeater like it sounds like you are wanting to do. You just need to get a duplexer if you only have a single repeater.

Thanks! Ya I realize there are multicouplers and combiners involved. They have usually around six stations sharing an antenna and they use tower top amps on all the receive antennas. I’m sure it gives them better control of the entire system to separate RX and TX antennas like that.

I’m looking at a Telewave ANT150D for the antenna along with a duplexer. Then an intermod panel… so still a couple of grand from a completed system…

-B

 

[mmckenna]

Thanks! Ya I realize there are multicouplers and combiners involved. They have usually around six stations sharing an antenna and they use tower top amps on all the receive antennas. I’m sure it gives them better control of the entire system to separate RX and TX antennas like that.

Is this an 700 or 800MHz trunked system?

 

[BMDaug]

Is this an 700 or 800MHz trunked system?

Yes, seems to be both. I think that’s part of why it works so well. You’ve got 30MHz or 45MHz between RX and TX and they still filter. There’s usually 60dB or better separation.

Edit: The band plan is around 82X.XXXX -45 and 77X.XXXX +30

-B

 

[mmckenna]

There's your answer. The transmit combiners/receive multicouplers have some filtering, plus, as you noted, the 45MHz offset.

Won't work on VHF, just not enough separation. A duplexer and use the full antenna is the way to go.

 

[BMDaug]

There's your answer. The transmit combiners/receive multicouplers have some filtering, plus, as you noted, the 45MHz offset.

Won't work on VHF, just not enough separation. A duplexer and use the full antenna is the way to go.

Thanks again for your help! That’s what I’m gonna do… Please just to help me understand though… the state uses 30MHz and 45MHz offsets in the ~800MHz band. Isn’t this pretty close to the same actual spacing (using a unit of measure like centimeters) as 7MHz in the VHF band? My frequencies are ~152MHz and ~159MHz. I’m not sure what words to use to properly convey what I mean. Ya, you’re talking about 30-45MHz, but that’s with little tiny 800MHz wavelengths… I’m at 7MHz offset with much like longer wavelengths. Does RF not work this way?

I’m not trying to argue with you, here. I’m going to take your build advice for sure, I’m just trying to learn.

Thanks,
Brian

 

[mmckenna]

Thanks again for your help! That’s what I’m gonna do… Please just to help me understand though… the state uses 30MHz and 45MHz offsets in the ~800MHz band. Isn’t this pretty close to the same actual spacing (using a unit of measure like centimeters) as 7MHz in the VHF band? My frequencies are ~152MHz and ~159MHz. I’m not sure what words to use to properly convey what I mean. Ya, you’re talking about 30-45MHz, but that’s with little tiny 800MHz wavelengths… I’m at 7MHz offset with much like longer wavelengths. Does RF not work this way?

I’m not trying to argue with you, here. I’m going to take your build advice for sure, I’m just trying to learn.

Thanks,
Brian

700MHz LMR band is 30MHz spacing
800MHz LMR band is 45MHz spacing.

You could run separate antennas on VHF, but you would need the filtering to keep the TX out of the RX. Since you are not using a trunked system with TX combiners with filtering and RX multicouplers with filtering, you still need to have some filtering. That's where you either need a lot of vertical separation or the duplexer.
The duplexer works much better than vertical separation since it keeps the TX and RX antenna in the same place so the coverage is the same. It also means you don't have to pay for two antennas and two feedlines on the tower. Some tower sites might charge you per antenna linear foot and for each run of coax up the tower. Usually duplexers are cheaper.

With 7MHz of separation, you shouldn't need super expensive duplexers.

 

[prcguy]

Your looking at a single dipole for a VHF repeater? That's 0dBd gain and would only be a good idea if the repeater is on a 6,000ft mountain and you need some coverage at the base. Most of the performance and range comes from the antenna not the repeater or other hardware.

Thanks! Ya I realize there are multicouplers and combiners involved. They have usually around six stations sharing an antenna and they use tower top amps on all the receive antennas. I’m sure it gives them better control of the entire system to separate RX and TX antennas like that.

I’m looking at a Telewave ANT150D for the antenna along with a duplexer. Then an intermod panel… so still a couple of grand from a completed system…

-B

 

[Cameron314]

No, these were RG-6. I grabbed the reel of cable when they were going to throw it out. I used it to move a satellite internet dish at one of our remote sites. It was many years ago, however. I -do- know the difference between twisted pair and coaxial cable at this point in my career.

Well I was talking about Speedway's picture, didn't see notice yours I guess. If you had a pair of RG-6 it was likely the old Cisco's.

 

[BMDaug]

Your looking at a single dipole for a VHF repeater? That's 0dBd gain and would only be a good idea if the repeater is on a 6,000ft mountain and you need some coverage at the base. Most of the performance and range comes from the antenna not the repeater or other hardware.

Thabks… so, one of these is what I am looking at. All of the available sites are at around 9-10,000 feet and I do need coverage from the tower to the valley floor and up the other side of the valley. One of the sites is kinda at the ‘end’ of the valley where he river turns so in that case, I’d be shooting for a narrower and longer pattern. I’m definitely open to suggestions!!

-B

 

[speedway_navigator]

because someone moved in and used rg58 for two 60’ runs in opposite directions to a couple of yagis that they just laid in some trees… Something about repeating a TV station?

Sounds like a passive repeater, use one on a UHF system to get coverage down a hall off the main floor of the Superdome.