Best upgrade for two repeater system

[prcguy]

Yes, most duplexers will pass two channels 50KHz apart with no problem. The receive multicoupler would basically be a two way divider and low noise high IP1/IP3 preamp with low gain. Here is a pic of the TX combiner I bough cheap used that would combine two transmitters 50KHz apart into a single duplexer. I still think a dual slot Mototrbo/DRM solution is the best.

Edit: That is not my specific TX combiner as its missing the 3dB hybrid, mine looks identical but with the hybrid mounted against the front panel.

In this situation I would avoid separate TX and Rx antennas entirely.

Use the two channels 50KHz apart.

I had the opportunity to look at a 4 channel NXDN trunk system. It uses a single antenna, with a 6 cavity ResLoc. All 4 transmitters we’re combined to a single feedline, to the low pass side of the duplexer, all the receivers were combined with a receive multicoupler fed from the High pass side of the duplexer.

Crecend amplifiers, Sinclair transmit combiner, Sinclair dual circulators , Sinclair receive multicoupler, Sinclair Duplexer.


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[buddrousa]

Read post 5 of the OP

 

[kayn1n32008]

Read post 5 of the OP

What about it?



He’s using 2 pairs 13MHz apart. There is so much wrong with his setup. 2 repeaters blasting 50w, into Chinese mobile duplexers, using LMR400 for cabling.

I’m surprised it even works at all.

He said he has 2 pairs 50KHz apart he’s not using.

Use them, combine the transmitters, multicoupler the receivers, out a high quality duplexer in tuned to pass both pairs 50KHz apart, and use quality feedline, and double shield jumpers. Cut the power back to 25w and he should have around 10w to the feedline. He could even use the Chinese duplexer(dummy load on the other port) as a notch filter to give more isolation to the receiver from the two transmitters.

Simple, clean and not complicated. No need for dual antennas. Easy to set up on site.

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[prcguy]

This is what I would consider the best option, however, he has a Mototrbo repeater and it should be able to do two time slots or two simultaneous conversations on one frequency pair without having to buy any hardware.

What about it?



He’s using 2 pairs 13MHz apart. There is so much wrong with his setup. 2 repeaters blasting 50w, into Chinese mobile duplexers, using LMR400 for cabling.

I’m surprised it even works at all.

He said he has 2 pairs 50KHz apart he’s not using.

Use them, combine the transmitters, multicoupler the receivers, out a high quality duplexer in tuned to pass both pairs 50KHz apart, and use quality feedline, and double shield jumpers. Cut the power back to 25w and he should have around 10w to the feedline. He could even use the Chinese duplexer(dummy load on the other port) as a notch filter to give more isolation to the receiver from the two transmitters.

Simple, clean and not complicated. No need for dual antennas. Easy to set up on site.

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[kayn1n32008]

This is what I would consider the best option, however, he has a Mototrbo repeater and it should be able to do two time slots or two simultaneous conversations on one frequency pair without having to buy any hardware.

I believe he is already doing that. He states capacity plus in his op.


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[pboyd]

How bout using one Mototrbo/DMR repeater and running two time slots? One repeater, one modest duplexer, one antenna, two individual comm channels, no problems.

We're actually using the capacity plus feature and all 4 time slots for multiple talk groups. We're a little event but all the volunteers seem to love having a radio on their hip. So it's serving more than 100 portables. We're well beyond the 2 time slots.

 

[pboyd]

He’s using 2 pairs 13MHz apart. There is so much wrong with his setup. 2 repeaters blasting 50w, into Chinese mobile duplexers, using LMR400 for cabling.

I’m surprised it even works at all.

He said he has 2 pairs 50KHz apart he’s not using.

Use them, combine the transmitters, multicoupler the receivers, out a high quality duplexer in tuned to pass both pairs 50KHz apart, and use quality feedline, and double shield jumpers. Cut the power back to 25w and he should have around 10w to the feedline. He could even use the Chinese duplexer(dummy load on the other port) as a notch filter to give more isolation to the receiver from the two transmitters.

Simple, clean and not complicated. No need for dual antennas. Easy to set up on site.

I just checked my settings this weekend for the first cable test of the new trailer (yes, I went with Heliax superflex, so no more LMR400 except for the jumpers between the repeaters and the duplexer). The repeaters are only running at 35W out of their 50W max, digging through my notes someone told me to not use all 50W due to noise issues so I turned them down.

How would plugging both repeaters into the same antenna work? Go through the same duplexer (just get a better one)? A multicoupler on the receive side, but how do I prevent the transmitters from just feeding power into each other? Most combiners I've seen have a minimum frequency separation of about 250KHz...

 

[radioman2001]

Before you do anything like you are suggesting make sure you are operating properly with a single channel through one duplexer and one antenna. You first must make sure you are not interfering with your self, a good test is to have someone go to a marginal location and call in with the repeater disabled meaning no transmit. Then while that person is giving a 10 count turn the transmitter on, there should be no difference in the quality of the signal received. If there is noise with the transmitter or that person disappears on you you need to address that first before doing anything further. Another thing to try is lower you power to 5 to 10 watts, the portables with helical antenna is only putting out about 2-3 watts, and you may not need all that extra power that does raise the noise floor and then requires more isolation.

 

[pboyd]

Before you do anything like you are suggesting make sure you are operating properly with a single channel through one duplexer and one antenna. You first must make sure you are not interfering with your self, a good test is to have someone go to a marginal location and call in with the repeater disabled meaning no transmit. Then while that person is giving a 10 count turn the transmitter on, there should be no difference in the quality of the signal received. If there is noise with the transmitter or that person disappears on you you need to address that first before doing anything further. Another thing to try is lower you power to 5 to 10 watts, the portables with helical antenna is only putting out about 2-3 watts, and you may not need all that extra power that does raise the noise floor and then requires more isolation.

What frequencies would you suggest for this test? Just any of my simplex frequencies? The portables normal transmit frequency for the repeaters (Repeater RX)? Or the repeater TX?

I don't think I can use repeater TX because of the repeater will send the time slot heartbeat even when not transmitting and that can cause some weirdness with other transmitters on the same frequency right?

 

[kayn1n32008]

I just checked my settings this weekend for the first cable test of the new trailer (yes, I went with Heliax superflex, so no more LMR400 except for the jumpers between the repeaters and the duplexer). The repeaters are only running at 35W out of their 50W max, digging through my notes someone told me to not use all 50W due to noise issues so I turned them down.

How would plugging both repeaters into the same antenna work? Go through the same duplexer (just get a better one)? A multicoupler on the receive side, but how do I prevent the transmitters from just feeding power into each other? Most combiners I've seen have a minimum frequency separation of about 250KHz...

35w is over kill for a system that serves portables

You need a combiner similar to this:

Sinclair Technologies Online Product Catalog - TC3112

Minimum separation is 0KHz.

Use your 50KHz pairs with a duplexer like this:

Sinclair Technologies Online Product Catalog - Q301GR-2

That duplex gives minimum 100dB isolation @ 700Khz separation.

It should be tunable to pass both pairs.

Rx Multicoupler to the high pass port and the transmit combiner to the low pass port.


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[radioman2001]

Ok for the testing set one the repeaters and some portables up for a repeater channel that you have licenced in analog (assuming you have that capability and EID) and run the test as described. The radio will give you the answeres as I have described above, and once you are comfortable that the repeater is not causing desense (term for noise of a receiver caused by a transmitter) reprogram back into digital.

 

[pboyd]

35w is over kill for a system that serves portables

You need a combiner similar to this:

Sinclair Technologies Online Product Catalog - TC3112

Minimum separation is 0KHz.

Use your 50KHz pairs with a duplexer like this:

Sinclair Technologies Online Product Catalog - Q301GR-2

That duplex gives minimum 100dB isolation @ 700Khz separation.

It should be tunable to pass both pairs.

Rx Multicoupler to the high pass port and the transmit combiner to the low pass port.


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Wow.... 20U just for the duplxer? What about something like the Q3330C-2 instead? I don't really have 20U of space to spare in the rack, especially not if I ever need to expand to 3 repeaters...

 

[kayn1n32008]

Wow.... 20U just for the duplxer? What about something like the Q3330C-2 instead? I don't really have 20U of space to spare in the rack, especially not if I ever need to expand to 3 repeaters...

Absolutely you could. Keep in mind the Q3330 series duplexes can be mounted vertically or horizontally. The rack mount wings are switchable. With the Q3330C, You take a 15dB hit in isolation, over the round cavity duplexer, but 85dB should be more than adequate, especially if you are only running 20-25w of transmit power.

Spitballing here, worse case, with the transmit combiner @3.9dB loss, 1.2dB loss for the duplexer and another 1dB loss for connectors, you are a shade over 6dB if system loss on transmit before the feedline going to the antenna.

@25w transmit power, you still have ~6.25w headed to the antenna. Throw a 3-6dB gain antenna up and that should give you a fairly well balanced system using 4w portables. Especially using DMR. The biggest stumbling block to talk out/talk in distance is going to be your antenna elevation.

Keep in mind the specs Sinclair gives are worse case. Anyone with a bit of skill and patience can easily exceed their specifications for loss and isolation.



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[speedway_navigator]

I'm curious how many over 100 users you have, a 25 user to 1 slot ratio is pretty high. When I was with Beacom we did events with 400+ users with 8 slots.

 

[pboyd]

I'm curious how many over 100 users you have, a 25 user to 1 slot ratio is pretty high. When I was with Beacom we did events with 400+ users with 8 slots.

Looking at last years numbers we had about 135 portable radios. I've been standing in front of the repeater and watched 3 of the 4 time slot lights turn on at once so I know for a fact that we use at least that many time slots. I've also been trying to find some solution to monitor how many slots we are using so that I can tell how often (if at all) we actually hit 4 slots to see if we actually need to bump up to 3 repeaters (I don't actually think we do, just my paranoia).

 

[speedway_navigator]

Bearcom was using this when I left them in 2014, there are probably other vendors.
https://genesisworld.com/product/trbo/

I was going to run wireshark on a managed switch to look at the packets flying around to see how hard it would be to gather stats but never got around to it. I bet a Raspberry Pi could be configured to do this monitoring.

 

[slicerwizard]

I've also been trying to find some solution to monitor how many slots we are using so that I can tell how often (if at all) we actually hit 4 slots to see if we actually need to bump up to 3 repeaters

Hm, just log the rest channel data with DSD+ and if the rest channel number field changes to zero, i.e. no rest channel present/available, you have an ATB situation. Takes one laptop and one SDR dongle.

 

[TampaTyron]

I can confirm the Genesis product works well if your pockets are deep enough to deal with it. It requires an IP connection to the site (or it can reside on site). TT

 

[pboyd]

Hm, just log the rest channel data with DSD+ and if the rest channel number field changes to zero, i.e. no rest channel present/available, you have an ATB situation. Takes one laptop and one SDR dongle.

Haven't played with DSD in a while. Will have to give it a shot.

 

[pboyd]

Thanks for the advice all. So far I changed from the LMR400 to the Heliax Superflex and with that as my only upgrade the RSSI when not transmitting on the other repeater went down about 10 dBm and when transmitting on the other repeater the value went down about 25 dBm from prior measurements.

This was just at a smaller training event with a lower noise floor than our normal event, but I'm definitely encouraged by that improvement.