Duplexer for commercial radio monitoring

[Prospect62]

Hey guys, I'm sorry if this is a duplicate question. I've done some reading here and I just want to get opinions on my particular needs, if you guys have time.

I have two GE Orion radios. One VHF 150-174 and one 800 MHz EDACS. I live and work about two miles from the EDACS tower site and my county's VHF system is very strong. I will be using these for monitoring purposes 99% of the time. I also have a low band radio that I will be using. This will be a vehicle installation and I will be installing two 1/4 wave NMO antennas on the roof of my vehicle. I'd like to tie the VHF and 800 together into one antenna and use the other NMO for the low bander.

Could I combine the VHF and 800 radios into one antenna using this:

TNC Male Plug to Y 2X TNC Jack Female Splitter Combiner Pigtail RG316 1M2F | eBay

OBVIOUSLY with the male and female ends reversed. Or could I use this:

RF Connector Combiner Splitter 2 BNC M to BNC F | eBay

OBVIOUSLY with some TNC to BNC adapters.

Or, should I pony up and get a more expensive combiner/splitter? If so, suggestions on that? Most of the ones that have been recommended on here before are no longer available as the threads and links are like 5 years old.

Thanks for any help!

 

[prcguy]

Think about what will happen if you connect two transceivers together with a common antenna cable. If you transmit on one it will feed much of the power right into the others receiver and probably damage it.

If you use that setup for receive only then you have one problem of the signal splitting to two different radios and about 50% of your receive signal will be lost in splitting, plus there will be additional loss splitting with a T adapter where two 50 ohm receivers are connected to a single 50 ohm antenna cable and presenting a 25 ohm load.

If you use an actual splitter or power divider designed for your frequency range you will still loose 50% or 3dB of the signal to each radio and you still can't transmit without damaging a receiver or the splitter.

A diplexer is a device with high pass/lo pass filters which will allow you to connect two transceivers of different bands to a multiband antenna with minimal loss and you can transmit on either radio. The insertion loss through most diplexers is very small like .2dB and that's the right way to do what you want.

Here is one that should work for your application: Comet CF 416W Duplexer w Leads 1 3 250MHz 440 1400MHz | eBay
prcguy

Hey guys, I'm sorry if this is a duplicate question. I've done some reading here and I just want to get opinions on my particular needs, if you guys have time.

I have two GE Orion radios. One VHF 150-174 and one 800 MHz EDACS. I live and work about two miles from the EDACS tower site and my county's VHF system is very strong. I will be using these for monitoring purposes 99% of the time. I also have a low band radio that I will be using. This will be a vehicle installation and I will be installing two 1/4 wave NMO antennas on the roof of my vehicle. I'd like to tie the VHF and 800 together into one antenna and use the other NMO for the low bander.

Could I combine the VHF and 800 radios into one antenna using this:

TNC Male Plug to Y 2X TNC Jack Female Splitter Combiner Pigtail RG316 1M2F | eBay

OBVIOUSLY with the male and female ends reversed. Or could I use this:

RF Connector Combiner Splitter 2 BNC M to BNC F | eBay

Or, should I pony up and get a more expensive combiner/splitter? If so, suggestions on that? Most of the ones that have been recommended on here before are no longer available as the threads and links are like 5 years old.

Thanks for any help!

 

[mmckenna]

Even with a proper diplexer, there's going to be losses.

If at all possible, each radio should get it's own properly tuned antenna. It'll work better. It'll let you tune each antenna. It'll save you money.
A "good" diplexer" is going to be more than having an additional NMO mount installed.

 

[Prospect62]

Well thank you guys both for your input.

If you transmit on one it will feed much of the power right into the others receiver and probably damage it.

Good point. Don't know how I forgot to consider that.

I'll be installing my own NMOs so the only thing costing me money is mounts, coax and the antenna itself. I just don't want three antennas on the roof of my truck. Two is pushing it. Maybe I can come up with a clever alternative for the third antenna. What I don't forsee is spending more than $50 on a diplexer.

 

[cmdrwill]

For UHF and VHF the Comtelco DBD1 diplexer.

 

[mmckenna]

VHF antenna in the center of the cab roof.
800MHz antenna near the back of the cab roof.
Low band antenna on a bracket from the front fender. - or, 1/4 wave whip off the side.

I'm running VHF and 800MHz on my truck. It's a crew cab, so I've got lots of real estate to deal with. VHF 1/4 wave whip is mounted smack in the center (left/right and front/rear).
The 800MHz 1/4 wave whip is mounted near the rear of the cab. The higher frequency needs less of a ground plane. That, and the 1/4 wave 800MHz whip is about 3 inches tall, so it's not really noticeable.

 

[Prospect62]

VHF antenna in the center of the cab roof.
800MHz antenna near the back of the cab roof.
Low band antenna on a bracket from the front fender. - or, 1/4 wave whip off the side.

I'm running VHF and 800MHz on my truck. It's a crew cab, so I've got lots of real estate to deal with. VHF 1/4 wave whip is mounted smack in the center (left/right and front/rear).
The 800MHz 1/4 wave whip is mounted near the rear of the cab. The higher frequency needs less of a ground plane. That, and the 1/4 wave 800MHz whip is about 3 inches tall, so it's not really noticeable.

Good configuration. That was my plan for the roof until I got this low band cheap and decided to toss it in. The low band will be strictly for monitoring, I have ZERO chance of transmitting on it.