Best upgrade for two repeater system

[Project25_MASTR]

Man, I'm quite late to this one. @pboyd as you've discovered, flat pack duplexers desense (transmit leaks into receive) when they get more than 35W in them (even the higher end EMR and RFS duplexers suffer it). I typically run about 32W out of the duplexer in that application. While I don't like it, one of the standard practices for my employer is to utilize dual ANT450D antennas spaced roughly 5 feet apart (vertically) for a Capacity Plus system (they've even done that for 3 channel systems). I'm not a big fan of high gain antennas (I actually prefer 0 dBd most of the time) and as mentioned, you are dealing with radios with a 4W uplink...power doesn't really mean a ton.

One thing you can also look into (though its pricey) is something like the RFI MiniSystem Combiner (SP model which has a single antenna for both receive and transmit). A little lossy (~8 dB) but again 4W uplink is the weak link. Only catch is their window filter is only 1.2 MHz wide so all of your frequencies have to be within that window but it does allow one to use a single RX/TX antenna.

 

[cmdrwill]

Get rid of anny and all LMR400 or any LMR type cables. Make sure all connectors are top quality, no CCJ. No adapters ect.

 

[pboyd]

Get rid of anny and all LMR400 or any LMR type cables. Make sure all connectors are top quality, no CCJ. No adapters ect.

If you read two posts ago you'll see that's what I did. It resulted in some pretty significant improvements in the RSSI noise floor and when the other repeater is keyed up. Hopefully the test event results will be similar to the real event.

 

[kjl13]

What is the frequency separation of the repeaters? Mobile duplexers are useless for close spaced repeaters and frankly any two repeaters within the same band with close spaced antennas. If your frequencies are very close together like less than 1 MHz, I would consider a hybrid type transmitter combiner and receiver combiner with adequate receiver preselector and dedicate one antenna for transmit and one for receive.

If frequencies are a MHz or more apart I would consider band pass/notch type duplexers to help keep the transmitter of one repeater from desensing the other. You should also have isolators on each transmitter to reduce the chance of creating Intermod when both transmitters are keyed up. Use good quality double shielded coax on all RF paths from the repeaters to any duplexer, combiner, etc. RG-142, RG-400 or RG-214 is standard.

Loose the LMR-400 or any LMR type cable in the RF path. It can create low level Intermod problems due to the dissimilar metals used inside the coax. Go with RG-213 or RG-214 or Superflex Heliax, anything but LMR coax.

Finally, the overall range of the repeater will depend heavily on the antenna(s). Get the biggest, longest, highest gain commercial quality antennas you can carry and put up.

Get rid of anny and all LMR400 or any LMR type cables. Make sure all connectors are top quality, no CCJ. No adapters ect.

What do you not like about LMR(presuming it is Times Microwave), I have heard great things about people using Times Microwave LMR-1200 for repeaters?

 

[kayn1n32008]

What do you not like about LMR(presuming it is Times Microwave), I have heard great things about people using Times Microwave LMR-1200 for repeaters?

Run of the mill LMR-400 has a foil shield as well as a braided shield. They are different metals. In full duplex installations, it can generate PIM.

There is a low-PIM version of LMR400, but at that point, you may as well just move up to 1/2” hardline.

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[12dbsinad]

I'll also add that usually LMR-400 will work great when it's brand new. As it ages it will start to give you trouble.

Anytime you run full duplex through a piece of coax, or any coax cabling on a repeater system, you can't just throw up some elcheapo stuff you'd use in a vehicle or a base antenna.

 

[kjl13]

Run of the mill LMR-400 has a foil shield as well as a braided shield. They are different metals. In full duplex installations, it can generate PIM.

There is a low-PIM version of LMR400, but at that point, you may as well just move up to 1/2” hardline.

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Ah. So you are talking about LMR400 only.


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[kjl13]

I'll also add that usually LMR-400 will work great when it's brand new. As it ages it will start to give you trouble.

Anytime you run full duplex through a piece of coax, or any coax cabling on a repeater system, you can't just throw up some elcheapo stuff you'd use in a vehicle or a base antenna.

Well. Times Microwave LMR is still pretty great in general, and they have better cables then LMR 400.


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[Project25_MASTR]

Ah. So you are talking about LMR400 only.


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All LMR (minus the low-PIM stuff) is constructed the same way. CCA core, aluminum foil shield and a silver clad copper braid. Due to the dissimilar metals on the shielding, it can be a PIM nightmare, especially as the coax ages and absorbs moisture.

Typically, intermod becomes audibly noticeable after a few years on an analog repeater using LMR type coax. Great for half duplex environments but should not be used in full duplex application unless you want to replace every few years.


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[12dbsinad]

Well. Times Microwave LMR is still pretty great in general, and they have better cables then LMR 400.


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It doesn't have really anything to do with the manufacturer, it's all on the materials used and construction of the cable. Any elcheapo 9913, LMR400 type cable is terrible for full duplex. I say elcheapo because good double shielded cable like RG214 is more than twice the cost.

And you're right, they do have better cable. It's called hardline.

 

[radioman2001]

LDF4-50A is the lowest type of cable I would use on UHF, and only on runs under 100ft. At 100ft on UHF (450-470) you are at 1.5db loss just for the cable, and add 1.5db per connector. Add more for any type of jumper you use. I try and go directly (after lightning protection) right into the duplexer "T".
If you can still find them get the brass connectors instead of the newer style ones. We have just recently started to use the newer style ones so I cannot give a report on how they last.

 

[12dbsinad]

If you can still find them get the brass connectors instead of the newer style ones. We have just recently started to use the newer style ones so I cannot give a report on how they last.

We use tons of RFS cable. The newer connectors are not as good IMHO, especially Andrew. I am a fan of the old brass solder on center pin connectors, not the new self flaring compression center pin connectors. I just don't find them to make a "good" connection like a solder on, but maybe I'm old school..

 

[speedway_navigator]

I just don't find them to make a "good" connection like a solder on,

Have you seen differences in return loss tests?
Pboyd's results were the first I've seen with real data points, nice to have that info

 

[12dbsinad]

Have you seen differences in return loss tests?
Pboyd's results were the first I've seen with real data points, nice to have that info

Return loss is typically good. The problem we've found is when you apply real world RF in a full duplex environment, also with age and/or mediocre installation practices, noise can be generated by movement of the connector.

The same problem is plagued with VHF Super Station Master antenna's. They use a compression type connection between the internal support pipe tube and the actual radiating sections of the antenna. When it's new, all is typically good. When it becomes 5 or more years old, watch out when the wind blows because you'll have a severe case of the "crunchies"