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Methods for finding the quietest frequency during coordination

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BonziBuddy

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Say your licensing a customer for a repeater pair. The local frequency coordination company gives you several UHF 450/460 repeater pairs to choose one from. It is your job to find the "quietest" frequency.

How would YOU go about doing this? What equipment would you use? (assume the repeater antenna is installed and you'd be listening on that)

I'm thinking I'd use an audio logging recorder recording separate channels of audio from individually programmed commercial radios each listening on one of the possible frequencies. Put it up at the future repeater location and let it sit for a week. Check it after a week and see which frequencies were the quietest.

How has this been done in the commercial LMR world in the past? Is there any equipment out there that has been designed for this purpose? Has any of this equipment recorded PL/DPL history at the same time?
 

GrumpyGuard

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I would suggest using a scanner such as the Pro106 that will count the amount of times each frequency is used. Although you might want a scanner for each frequency for accuracy.
 

BonziBuddy

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I would suggest using a scanner such as the Pro106 that will count the amount of times each frequency is used. Although you might want a scanner for each frequency for accuracy.
That's worth a try.

I considered using a BCD536HP which could be set to scan the frequencies in question and record individual clips of received audio. Then I'd tally up all the recordings in excel and see what frequency pair has the lest co-channel users.

One of the concerns with this is that I've found the BCD536HP opens squelch at around .3uv which isn't sensitive enough. The squelch adjustment doesn't seem to help either, it just adjusts squelch tight, not squelch open.

The other issue is getting false or inaccurate readings. I might put the scanner up on location and 5 minutes after I leave it might get stuck on a control channel or something.

I have a huge heavy logging recorder and several CDM's which I'm considering wiring up for this, but if it takes too much time and energy I'd just try the scanner idea and see how that works out.

Several Pro106's and a receiver multicoupler is certainly an idea.
 

ecps92

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And don't just listen to the Repeater output, also listen to the Repeater input as there are plenty of simplex users on the inputs

I would suggest using a scanner such as the Pro106 that will count the amount of times each frequency is used. Although you might want a scanner for each frequency for accuracy.
 

12dbsinad

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And don't just listen to the Repeater output, also listen to the Repeater input as there are plenty of simplex users on the inputs
Yes, be more concerned with the repeater input versus the output. Whatever you hear on the input is what the repeater will hear all the time. For instance, if there is a licensed simpex user on the input that is very strong, and you have a handheld radio with okay but not a great signal, it is possible that the simplex user would "wipe out" your transmission or sound like 2 units trying to talk at the same time. Do however check the output freq as well.

Program a good spec mobile radio and connect it to the repeater antenna on the input. Don't use a scanner as those receivers are "funnels" and will overload easily. This is what the repeater will hear (or possibly even better) at all times. Also, do a search on the ULS for the input freq and see what is licensed around you.
 

BonziBuddy

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And don't just listen to the Repeater output, also listen to the Repeater input as there are plenty of simplex users on the inputs
Yes, be more concerned with the repeater input versus the output. Whatever you hear on the input is what the repeater will hear all the time. For instance, if there is a licensed simpex user on the input that is very strong, and you have a handheld radio with okay but not a great signal, it is possible that the simplex user would "wipe out" your transmission or sound like 2 units trying to talk at the same time. Do however check the output freq as well.

Program a good spec mobile radio and connect it to the repeater antenna on the input. Don't use a scanner as those receivers are "funnels" and will overload easily. This is what the repeater will hear (or possibly even better) at all times. Also, do a search on the ULS for the input freq and see what is licensed around you.
Yep I had planned on paying more attention the inputs than the outputs. 4 pairs were offered, so I figured I'd listen to the inputs right off the bat, that way I could rule out the less desirable pairs first. Then I'd listen to the outputs which are part of promising pairs.

As far as the FCC database, I should mention that this repeater will be going up in an suburban area which has a beautiful unfortunate view of the Manhattan skyline.

I feel that when it comes to frequency choosing when your within RF range of NYC, don't stress the FCC database TOO MUCH, since it may not be realistic information. NYC seems to be a frequency free-for-all. Many expired licenses still being used, wide-band users with no intent to narrowband, and Joe Shmoe's radio shop picking frequencies out of their you know what. I will check the database again, but when you have to account for receiving RF from Manhattan, that's a lot of co-channel users on every pair to begin with, so listening on the frequencies will definitely help I think.

In case anybody's wondering why I'm asking this here, the customer isn't mine. It's through the company I work for, and I'm not the primary rep on the job. The primary tech is letting me basically go at it myself in a theoretical way and then critique me, so don't think to yourself this poor company is at the mercy of the radioreference forum lol.
 

12dbsinad

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Yep I had planned on paying more attention the inputs than the outputs. 4 pairs were offered, so I figured I'd listen to the inputs right off the bat, that way I could rule out the less desirable pairs first. Then I'd listen to the outputs which are part of promising pairs.

As far as the FCC database, I should mention that this repeater will be going up in an suburban area which has a beautiful unfortunate view of the Manhattan skyline.

I feel that when it comes to frequency choosing when your within RF range of NYC, don't stress the FCC database TOO MUCH, since it may not be realistic information. NYC seems to be a frequency free-for-all. Many expired licenses still being used, wide-band users with no intent to narrowband, and Joe Shmoe's radio shop picking frequencies out of their you know what. I will check the database again, but when you have to account for receiving RF from Manhattan, that's a lot of co-channel users on every pair to begin with, so listening on the frequencies will definitely help I think.

In case anybody's wondering why I'm asking this here, the customer isn't mine. It's through the company I work for, and I'm not the primary rep on the job. The primary tech is letting me basically go at it myself in a theoretical way and then critique me, so don't think to yourself this poor company is at the mercy of the radioreference forum lol.
Listening is the key. Listen using the established repeater antenna. Like I stated before, whatever is heard on the input is what will be heard all the time when the repeater is installed. So your goal is out of the 4 finding the least traffic or frequency of traffic givin your location. NYC is a tough one.
 

902

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Gentlemen, all of those methods might get you to step 1, but cannot assure you of successful certification of coordination.

I need to ask, is this for a business or public safety system? The methods used in determining a frequency are significantly different.

A business coordinator will place non-exclusive (non-FB8) systems with overlapping coverage and use the "shared use spectrum" clause of 90.175 to justify the action. As such, it is the licensees' responsibility to monitor before transmitting and share the frequency. Some technologies (like mixing legacy analog use with new TDMA [DMR, etc.] digital) don't play well with the sharing concept. Your frequency WILL have someone else on it. If you listen, you might be able to pick one or two that are relatively light. I know some oldtimers in the business who used to put up a receiver on a site with a community repeater tone panel, then display the number of tones used and the transmission duration time. Then they'd apply for the frequency that had the least amounts of airtime and tone hits.

A public safety coordinator will use R-6602 contours - for UHF - the proposed's 21 dBu F(50,10) "interference contour" vs incumbents' 39 dBu F(50,50) "service contour." If they intersect, the coordinator will require the proposed system to get a "letter of concurrence" from the incumbents. The smaller the footprint, or the more contained the antenna pattern, the better the chances of being approved with minimal difficulty. This doesn't always sink in at the manufacturer or service shop level.

The problem may be that incumbent systems are built to excess. A 1 square mile town building countywide coverage, for example, or the biggest antenna on the highest location using the highest power. Another problem is warehousing of spectrum. A secondary channel that's used once every two or three years might be a good example of that. STILL, it's protected and there's nothing currently that can be done about it. These frequencies will pass your scanner monitoring tests, but will fail frequency coordinator methodology.

A coordinator will "have to" give you something. For public safety, it's still something that might require action on behalf of the applicant (sometimes by requirement of the coordinator, sometimes by requirement of rule) to provide some sort of action to get it. Usually that is 90 days to follow a certain process of either getting a response, or producing certificate of service within a given time frame. After that, you start over.

One word of advice (free advice is always worth what it costs) - never put something on the air without at least securing a Special Temporary Authorization from the FCC. Yes, you "can" do it, and you "might" get away with it, and "probably" nothing will happen. The industry is largely self-policing, and when the Commission does respond to an interference complaint from an unlicensed source, it tends to look at the action as a potential revenue source. An ATM. An industry newsletter recently reported that the FCC had assessed $294,400 against Constellium Rolled Products Ravenswood, LLC for operating on expired licenses. There are other reports of various enforcement actions. Unlicensed operation (even expired license operation) usually requires a pretty good deal of committed resource to find and might be a little like poking a hibernating bear with a stick. Maybe it won't wake up, and maybe you can run faster than it can. Maybe not.
 
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I use an Icom R1500 with Spectrum manager software from scanstar.com

The program is buggy, even though I did the calibration routine every signal under -75 dBm shows up at -75 in the traffic analyzer mode.
The analog signal meter does show more accurate readings in basic scanning mode.

Once I get a list of unused freqs I scan those to verify, a full cycle takes about 9 seconds when I'm scanning the 12.5 kHz splitter freqs from 451-453 and 456-458.

I have been burned by a construction crew directing a crane operator, although my scan showed very little use once I got to the site I heard lots of short conversations like 'boom left', 'stop', 'down 10', 'stop'.
Because those transmissions were so short the scan missed them.

I did a scan in the Bronx in May for the half marathon, I did manage to find some freqs with little use.

I use Splashtop remote control so I can listen to the scanner without being on site.
 
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