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Author Topic: 2 Repeaters, One Frequency, Two Offsets  (Read 44929 times)

KJ6UHT

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2 Repeaters, One Frequency, Two Offsets
« on: June 11, 2014, 03:12:58 PM »

My local CERT group has acquired two repeaters, one running 100W and the other running somewhat less power. While CERT has been happily using our club repeater for many years, they now want their own, private/exclusive setup.

Given that we are in the SF Bay area (East Bay), there is only a single 2m frequency that appears to be available for coordination. So CERT says they plan to use both repeaters on the same frequency by varying their offsets.

I see nothing in section 97.205 that precludes this scheme. Am I missing something here? Are the CERT folks stepping into the doodoo - coordination-wise or technically?

Thanks!
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AA4PB

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #1 on: June 11, 2014, 04:29:25 PM »

The repeater with the non-standard offset may end up with the same input frequency as some other repeater. That means anyone transmitting on that frequency will potentially key up both repeaters. In addition, your existing repeater and the new CERT repeater will have an output on the same frequency thus they will still interfere with each other.

I think it would make more sense to put both repeaters on the same frequency pair (same offset) and use a different sub-audible tone for each repeater. That way a user can determine which repeater he will key up by selecting the proper tone frequency. It might also be helpful to activate the same tone on the repeater output so that users don't have to listen to the other repeater while monitoring. If you do that they will have to be disciplined enough to open their squelch and listen to make sure that the other repeater is not in use before they key up their own repeater.
 
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Bob  AA4PB
Garrisonville, VA

K4JJL

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #2 on: June 12, 2014, 07:33:15 AM »

I think it would make more sense to put both repeaters on the same frequency pair (same offset) and use a different sub-audible tone for each repeater. That way a user can determine which repeater he will key up by selecting the proper tone frequency. It might also be helpful to activate the same tone on the repeater output so that users don't have to listen to the other repeater while monitoring. If you do that they will have to be disciplined enough to open their squelch and listen to make sure that the other repeater is not in use before they key up their own repeater.

You just described a "community repeater".  Motorola has that as an option for some of their machines (aka MCS or multi-coded squelch).  Zetron makes a repeater controller that does this, also.

If you're running multiple transmitters, I can see that turning into a heterodyning mess that nobody is going to like.
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AA4PB

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #3 on: June 12, 2014, 10:56:08 AM »

I agree, if there is a lot of activity or their are undisciplined users then nobody is going to like two repeaters on the same frequency regardless of how you implement it. It also begs the question of why does the CERT group feel that they need their own repeater, even if its on the same frequency as the other repeater. If either the input or the output frequencies are duplicated then you can only use one repeater at a time.
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Bob  AA4PB
Garrisonville, VA

K4JJL

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #4 on: June 12, 2014, 11:26:57 AM »

t also begs the question of why does the CERT group feel that they need their own repeater, even if its on the same frequency as the other repeater.

The CERT guys here in S FL are usually on a GMRS repeater.  See if your local group will float that idea, too.
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KJ6UHT

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #5 on: June 12, 2014, 05:50:17 PM »

Wow! Thanks so much for the discussion.  Overall, it looks like a very bad idea - whether using different offsets or the same offset with different sub-audible tones.

Our club currently cover the whole island with a 10W 70cm repeater, and that has worked well. Two CERT repeaters pumping out a lot more power on 2m doesn't make sense to me (the island is only 4 miles long
and very flat). It would appear that there must be other factors at play.

Again, many thanks for reality check...
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NA4IT

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #6 on: June 13, 2014, 10:37:48 AM »

The MOST important thing you need to do... contact the repeater coordinating body. They can provide all the answers you need, and if it will coordinate, offer that protection to you. Trust me, it will save you tons of headaches.

It looks like NARCC is your coordinator... http://www.narcc.org/
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KJ6UHT

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #7 on: June 13, 2014, 04:26:13 PM »

Yup.  I have learned a lot, but you are absolutely right, the coordination issues really require early review by the folks who own that mandate. We are in the process of being coordinated (and, I am told, with encouraging feedback), but I am unclear whether this little complication has been raised so far in the process. :(
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KJ6UHT

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #8 on: June 13, 2014, 05:04:45 PM »

And K4JJL - I had not realized that GMRS repeaters were available ("duh"). That is an interesting suggestion.  Any recommendations, or maybe on-line pointers, about how well it works? While we have a lot of HAMs in CERT, we still have even more non-HAMs, and we provide GMRS training...
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K9MHZ

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #9 on: June 14, 2014, 04:55:50 AM »

I see nothing in section 97.205 that precludes this scheme. Am I missing something here? Are the CERT folks stepping into the doodoo - coordination-wise or technically?
Thanks!


Yeah, this sounds bad.  I know you guys are congested out there, but if you go against the coordination grain, you're just opening yourself up for a lot of sanctimonious blowback.  Part 97 gives you a lot of leeway in much of ham radio, but I don't think I'd use that as a reason to be cavalier.  You know how people are....they might never use a repeater themselves, but give them a cause and they're all over those evil elitist uncoordinated private repeater users.

Good luck.
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K4JJL

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #10 on: June 18, 2014, 07:15:13 AM »

And K4JJL - I had not realized that GMRS repeaters were available ("duh"). That is an interesting suggestion.  Any recommendations, or maybe on-line pointers, about how well it works? While we have a lot of HAMs in CERT, we still have even more non-HAMs, and we provide GMRS training...

It's going to work about as well as a 70 cm repeater, since they're so close in spectrum.  I've set up several for folks built out of old Motorola GR300s and MSF5000s.  About the only issue I've seen is people using mass-produced, bubble-pack radios with FRS duality having deviation issues. Bubble-pack FRS/GMRS radios are narrow band and the repeaters I mentioned are wide band.

Users will need to get GMRS licenses, too.
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N2HBX

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #11 on: June 22, 2014, 07:16:33 AM »

The dual input idea would work fine if by some dumb luck the repeater output was 147.000. Some places use the positive offset, others the negative.

73,
Larry, N2HBX
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KF7VXA

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #12 on: September 30, 2014, 12:32:35 PM »

There is a set of repeaters in Island Park, ID that uses the same input and output frequency's. Two different PL tones are required.
One has a PL of 100.0, the other 123.0.
One is for local use, the other is a part of the "Inner Mountain intertie" Not sure of the spelling, but the inner mountain intertie connects repeaters from Montana to Las Vegas together (maybe all the way to Phoenix, AZ, it was in the works some time ago).
It's about 100 miles from my QTH and I can access both with full quieting. It's a good repeater on a pretty tall mountain.
We have a local simplex GMRS repeater, just a commercial Motorola radio, duplexer and a set of cans with a vertical antenna. It's at almost 9000' and has a range in excess of 100 miles in many directions. It is on 467.550 with a PL code of 197.8 and works darn near as well as the amateur VHF/UHF repeaters in the same location.
What is also nice is that the building has a propane back up generator
John
« Last Edit: September 30, 2014, 12:54:39 PM by KF7VXA »
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KV4BL

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RE: 2 Repeaters, One Frequency, Two Offsets
« Reply #13 on: September 30, 2014, 12:57:27 PM »

Separate repeaters and/or inputs...

... when hard hats and orange or green vests just aren't enough.
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