Operating two UHF repeaters?

[hfd921]

my plan is to have a UHF repeater north and one south. If im in the middle of the two sites and key up on my radio will the closest repeater grab the signal and retransmit, or will both repeaters work against each against other,and gargle the transmission? if so ? what do i do to make the two repeaters work?

Thanks,

[mikegilbert]

Both repeaters will pick up the transmission and you will experience intermod. One trick would be to use a 'North' PL Tone and a 'South' PL tone in each radio. Both the North and South repeaters would output the same PL tone, but the input frequencies would have their own unique tone.

Example using GMRS frequencies:

North Repeater
462.575mhz 131.8hz output tone
467.575mhz 110.9hz input tone

South Repeater
462.575mhz 131.8hz output tone
467.575mhz 131.8hz input tone

One thing you'd have to do is reduce the repeater hangtime to eliminate brief periods of intermod when one user is talking in on the South and the other is on North.


A second option is to use a remote receiver on the North or South side. You'd have to get a voting comparator to 'vote' (compare the quality) the remote receiver against the repeater input. You'd need to setup a path to get the audio from one receiver to the main site though. The signal quality of the link has to be perfect, otherwise the system could reject the remote site thinking the signal is lousy.

You'll need:

Remote receiver
Voting Comparator
UHF or 900mhz RF link
-or- Microwave Link
-or Leased Line

[Bill_G]

Mike is exactly right, and his suggestion for multi-PL solution has been used many places successfully. Two repeaters set up the same within range of each other is a fubar generator. When you want to increase your coverage area, while having some overlap, you have to plan carefully.

[escomm]

Intermod from two carriers on the same frequency and PL you say?

[N4KVE]

Intermod from two carriers on the same frequency and PL you say?

I think he meant to say "doubling". Like 2 people transmitting at the same time is a "double". You 2 guys doubled. LOL. GARY N4KVE

[AEC]

Two repeaters using the same RX and TX frequencies wil generate on-carrier 'IMD' products as the mobile travels around, you will get varying signal strengths, meaning multi-path as well as addition of these same signals to create TDA effects(Time Difference of Arrival) products which affects reception drastically, especially in metro areas that have a lot of structures in the signal path.
Another method to minimize this distortion might be from using anennas on the opposite sides of towers across town, Ie: North tower, north side of tower, and same for the south tower.
Using tower shadowing can lower the signal mixing problem by a large margin, at times, better than 6 dB.

Shadowing may help with the overlap in your system's coverage, but can also be a problem to others to the north and south if there are systems on the same freq. pairings.
Simulcasting, as you are trying to create in a sense, needs both systems linked to GPS timing, such as a Spectracom, which will keep the transmit signals tied together, and at equal levels.
Timing helps stabilize the receivers so you do not have audio delays, which add to the roubles of having two strong carriers in a given area. Bad enough to have the mixing noise, but add distorted audio in along with it makes for severe coverage problems in the overlap zone.
Simulcast ops. are where high stability oscillators come into their own. You keep the off channel problems to a minimum, when both carriers have under .0025 frequency error.
Remember that if both channels are off by +/- XX Khz, the total error can be greater than 1-2 Khz, and that can cause audio dropouts as both additive and subtractive signals can cancel each other.
This will be highly apparent if you have one machine with a +1Khz error and the second with a -1Khz error...now you have a total error of 2Khz, which is close enough to cause carrier cancellation of transmitted audio if the mobile user has a standard 12.5K channel/2.5 K dev. There are methods and ways of dealing with simulcasting, and maybe these issues might be worh looking into for someoone wishing to atempt a dual system site plan. The aforementioned equipment is needed, but more can be added, as stated here. These are simply starting points.

[Will]

What happens is the capture affect of two transmitters on the same frequency at the same time.
So carrier beat is more correct in simple terms. And depending where you are the reception gets garbled. "What did you say, repeat".

We have been using the different input PL code for more than 30 years on two and three repeaters on the same frequencies. Covering three counties.
The big problem IS the operator who replies back on the wrong PL/repeater for where I am causing the carrier beat/capture affect.
What we did is add a different audible tone on each repeater output so the users would be able to tell what 'hill top' was in use.
It is still up to the users to match to the same 'hill top'/repeater.

[Bill_G]

Years ago I maintained a system like this, and we had that issue with the deputies not really knowing the best site to use for a given area, and walking on each other. I made a busy channel lock out ckt that monitored the output freq preventing repeater keyup when qualified. It stopped the accidental beating, but because there was no feedback to the user, like in a trunking system, sometimes they were talking to dead air because they couldn't hit the far repeater that was keyed. We took it out.

[KitN1MCC]

or maybe Go Trbo

[RFguy]

Intermod from two carriers on the same frequency and PL you say?

I think he meant to say "doubling". Like 2 people transmitting at the same time is a "double". You 2 guys doubled. LOL. GARY N4KVE

I think they meant to say heterodyne

[N4KVE]

Intermod from two carriers on the same frequency and PL you say?

I think he meant to say "doubling". Like 2 people transmitting at the same time is a "double". You 2 guys doubled. LOL. GARY N4KVE

I think they meant to say heterodyne

Yes, that's the word I couldn't think of. Thanks. GARY N4KVE

[hfd921]

Ok i see so just to confirm, Here is an example, below in the repeater would be as shown, to operate two repeaters what would I need to change on the second repeater to make them not work against each other, lets say this is the north repeater what should the south be? Different PL on South?

North

Channel 1 on the repeater is 461.0625 and then 466.0625 with a pl of 179.9

South

Channel 1 on the repeater is 461.0625 and then 466.0625 with a pl of ?

[Bill_G]

You got it. A PL of anything but 179.9.

[thebigphish]

...and not 179.8 or 180.0 Pick another full code entirely, not a nonstandard one near by.

[hfd921]

...and not 179.8 or 180.0 Pick another full code entirely, not a nonstandard one near by.

So i will have to operate as two channles? i with draw my last question......

I guess im just not that familiar with all this, i guess in larger systems thats why they are micrwave links, ect. ect. big bucks$$$

really what i want is to be able to key up on channel 1 and what ever repeater is closest pick up and re tx the message. example: im on the north side the north side ch1 gr300 repeater i want the southside ch1 motorola desktrac to get the message and re tx to the outter areas where the gr300 cant reach.... increasing my range.. i thought in theory i would just be relaying through repeaters to get more distance..

sorry if im confusing anyone.....

[Bill_G]

I discussed why you need PL in your other thread. As for programming, treat is as another channel. Chan 1 rptr north, chan 2 rptr south. Same freqs, different PL's.

[mikegilbert]

Any questions you may have were answered and spelled out clearly in my first post (aside from my intermod reference) d'oh!

[Bill_G]

...and not 179.8 or 180.0 Pick another full code entirely, not a nonstandard one near by.

So i will have to operate as two channles? i with draw my last question......

I guess im just not that familiar with all this, i guess in larger systems thats why they are micrwave links, ect. ect. big bucks$$$

really what i want is to be able to key up on channel 1 and what ever repeater is closest pick up and re tx the message. example: im on the north side the north side ch1 gr300 repeater i want the southside ch1 motorola desktrac to get the message and re tx to the outter areas where the gr300 cant reach.... increasing my range.. i thought in theory i would just be relaying through repeaters to get more distance..

sorry if im confusing anyone.....

You edited your questions after I replied earlier.

If you want user traffic in the north to be repeated on the north and the south repeaters (and vice versa) on a common output freq, then you need a simulcast system. If you thought microwave links were expensive, wait until you see the price tag on simulcast. This stuff isn't magic. There is nothing in the repeater logic that sorts out what is the most appropriate radio to repeat on. Two repeaters on the same channel without synchronization is a mess.

If, on the other hand, you have two repeaters on different freqs, then your request could be possible. You need a third set of freqs to use as a rf link between the sites, or phone lines, or dsl, or microwave, or wifi, or any number of ways to link two sites together. Plus the hardware to support it, and the logic that would control the radios at both sites. It's called multicasting, and totally doable. You would program your portables with two different freqs on two different channels. Your users would have to know where they were to make the best use of the system.

[hfd921]

thank you for the input.... as always , its nice to get strait to the point info from the experts...... i think i will work on updating and upgrading our gr300, maybe a higher tower and a better antenna...

[Bill_G]

No trouble at all. Mike Gilbert's first option solution in the first response to your OP is the simplest and easiest way to get some extra footprint. Lots of people have done it.