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Hello Group,
?
I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please
?
1. The repeater will be on the UHF spectrum of the ham radio side.
2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides.
3.? Height will be between 350 to 400 ft
5. Cable is 1 5/8" hard line that was run but never used and capped off.
4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded.
4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building.
5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark.
6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
?
Thanks!
Steven H.
N8RLW
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No problem....Ive have repeaters on broadcast towers for decades...VHF, UHF ...TV and FM... you're good
Hello Group,
?
I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please
?
1. The repeater will be on the UHF spectrum of the ham radio side.
2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides.
3.? Height will be between 350 to 400 ft
5. Cable is 1 5/8" hard line that was run but never used and capped off.
4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded.
4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building.
5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark.
6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
?
Thanks!
Steven H.
N8RLW
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You might consider adding an isolator to your uHF system between the TX output and cavities. Chances are you are not going to encounter any issues. I have had numerous 2m and 440 repeaters on broadcast towers for several years without any issue. Recently I did run into a problem with a 2-meter machine, but the ERP of the radio stations was much higher. We were dealing with three FM's combined onto a single antenna with a combined ERP close to 100kW. I had to install a FM trap on the repeater feedline to reduce the amount of RF getting into the system from the FM stations. We have about 250ft vertical separation between the broadcast array and the repeater antenna.
Sounds like you are going to have a great system!
73,
Kevin, K9HX
On Thu, Mar 13, 2025 at 10:50?AM Chris Boone WB5ITT via <setxtelecom= [email protected]> wrote: No problem....Ive have repeaters on broadcast towers for decades...VHF, UHF ...TV and FM... you're good
Hello Group,
?
I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please
?
1. The repeater will be on the UHF spectrum of the ham radio side.
2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides.
3.? Height will be between 350 to 400 ft
5. Cable is 1 5/8" hard line that was run but never used and capped off.
4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded.
4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building.
5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark.
6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
?
Thanks!
Steven H.
N8RLW
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Depending on your preferences… “best practices” are always open to interpretation. While there may not be any other 400MHz UHF gear on the tower today, that might not be the case tomorrow. I get mildly amused when something new shows up on a tower and other repeater owners suddenly have an issue they have to mitigate, that might take them months. Is an IM panel and rx filtering really overkill? ? Sometimes a simple stub may be placed to dump the broadcast (this has been covered recently on the list.) ? I run isolators on all my gear, which of course has a low pass on the tx side, and on the rx I almost always have a band pass. ? Matt AL0R ?
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From: [email protected] <[email protected]> On Behalf Of steven harvey via groups.io
Sent: Thursday, March 13, 2025 09:49
To: [email protected]
Subject: [repeater-builder] Running a Repeater on a FM Broadcast Tower ? I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please 1. The repeater will be on the UHF spectrum of the ham radio side. 2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides. 3.? Height will be between 350 to 400 ft 5. Cable is 1 5/8" hard line that was run but never used and capped off. 4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded. 4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building. 5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark. 6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
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You might want to consider an antenna that’s more commercial grade, like a Comprod, Sinclair, or Commscope exposed dipole array in the 2 or 4 bay variety.
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Sorry, Didn’t catch it was UHF. We run a Commscope DB-420 on our D-Star repeater on 444 mHz. It has 16 bays and a 9.1 dbd gain figure. It is cut for 450-470, but has plenty of sweep to reach into the amateur 70cm band. Bad news it’s a $3000 antenna. We bought ours for about 10% of that. A short time ago I saw one still in the carton for $800 listed online, but it didn’t stay listed for long …
You might want to consider an antenna that’s more commercial grade, like a Comprod, Sinclair, or Commscope exposed dipole array in the 2 or 4 bay variety.
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-->Look for another FM station 5 MHz away (88.7 or 98.7)...if there's none within 15-20 miles, you're probably ok...
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On 3/13/2025 10:48 AM, steven harvey via groups.io wrote: Hello Group,
I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please
1. The repeater will be on the UHF spectrum of the ham radio side.
2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides.
3.? Height will be between 350 to 400 ft
5. Cable is 1 5/8" hard line that was run but never used and capped off.
4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded.
4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building.
5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark.
6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
Thanks!
Steven H.
N8RLW
|
On Thu, Mar 13, 2025 at 12:39 PM, Jim Barbour wrote:
-->Look for another FM station 5 MHz away (88.7 or 98.7)...if there's
none within 15-20 miles, you're probably ok...
Oh Lord....??? many, many years ago a new ham repeater was coordinated on
147.21 at a local MAJOR site.? Nobody knew that there was a paging system
on 152.21...? and that particular system was not very active... But when both
were on the air simultaneously the mix trashed EVERY UHF repeater. (well,
the 470-476? and 506-512 systems were not affected)
?
The public safety people were NOT happy. ? Emphasis on the NOT.?
Neither were the various commercial UHF repeater owners.?
There was no easy solution.? The final fix was that the ham system ended up
running "upside down" (147.21 in, 147.81 out) for the next 30-35 years (until
the 152.21 paging system shut down).
?
Mike WA6ILQ
?
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A site I used to maintain had a Class A FM on 105.5, and a 250W FX on 100.5, with the same programming. It was in an industrial area with about 6 low profile 450mHz business repeaters near by. That caused all sorts of problems. We finally proved to two different land-mobile shops that the FM's were clean, as the problem signals didn't exist until their own repeater TX was added into the mix. Of course they were all using mobile style reject only duplexers. I suggested they coordinate non standard repeater pairs, but not sure if that was a viable option for them or not. Have not heard from any of them in several years.
On Thu, Mar 13, 2025 at 12:39 PM, Jim Barbour wrote:
-->Look for another FM station 5 MHz away (88.7 or 98.7)...if there's
none within 15-20 miles, you're probably ok...
Oh Lord....??? many, many years ago a new ham repeater was coordinated on
147.21 at a local MAJOR site.? Nobody knew that there was a paging system
on 152.21...? and that particular system was not very active... But when both
were on the air simultaneously the mix trashed EVERY UHF repeater. (well,
the 470-476? and 506-512 systems were not affected)
?
The public safety people were NOT happy. ? Emphasis on the NOT.?
Neither were the various commercial UHF repeater owners.?
There was no easy solution.? The final fix was that the ham system ended up
running "upside down" (147.21 in, 147.81 out) for the next 30-35 years (until
the 152.21 paging system shut down).
?
Mike WA6ILQ
?
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My old club has two repeaters at a cable company tower. The repeaters are 1VHF and 1UHF. There is a low power local access TV transmitter in there and two radio stations transmitters in there When the radio stations came in there after us one of them caused interference on our UHF repeater. When it was brought to their engineers attention he ordered a notch filter and it was added to the UHF repeater and that took care of it.
Les Keegan? N4LPK?
On Thursday, March 13, 2025 at 10:48:59 AM EDT, steven harvey <sharvey@...> wrote:
Hello Group,
?
I'm in the investigation stage of relocating a repeater to a FM broadcast tower site.??? I've been on several LMR towers and not had any issues but wanted to see if there is any best practices I could learn from on what equipment should be mandatory for being on a FM broadcast tower site.??? I have listed what I have so far.? Any additional equipment please
?
1. The repeater will be on the UHF spectrum of the ham radio side.
2. It will be running a Kenwood NXR-1800K2 repeater with TXRX duplexers with a 100DB isolation between sides.
3.? Height will be between 350 to 400 ft
5. Cable is 1 5/8" hard line that was run but never used and capped off.
4. Antenna will be a commander technologies fiberglass antenna being side mounted on the tower with polyphaser lightening protection attached and grounded.
4a.? Jumpers will be 1/2 hardline between the antenna and 1 5/8" and the same going into the building.
5.? The radio station broadcast on 93.7 a with a ERP of 37,000 Watts and there antenna is at the 550ft mark.
6.? There only two 800Mhz commercial antenna's on the tower and a couple of Wifi provider dishes.?? I'll be above all of that equipment.
?
Thanks!
Steven H.
N8RLW
|
Split antennas and a circulator would have fixed the problem.. or change in frequency too?
Chris WB5ITT?
On Thu, Mar 13, 2025 at 12:39 PM, Jim Barbour wrote:
-->Look for another FM station 5 MHz away (88.7 or 98.7)...if there's
none within 15-20 miles, you're probably ok...
Oh Lord....??? many, many years ago a new ham repeater was coordinated on
147.21 at a local MAJOR site.? Nobody knew that there was a paging system
on 152.21...? and that particular system was not very active... But when both
were on the air simultaneously the mix trashed EVERY UHF repeater. (well,
the 470-476? and 506-512 systems were not affected)
?
The public safety people were NOT happy. ? Emphasis on the NOT.?
Neither were the various commercial UHF repeater owners.?
There was no easy solution.? The final fix was that the ham system ended up
running "upside down" (147.21 in, 147.81 out) for the next 30-35 years (until
the 152.21 paging system shut down).
?
Mike WA6ILQ
?
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Commercial systems cannot operate on a non-standard split. It's mandated in part 90?
Chris WB5ITT?
On Thu, Mar 13, 2025, 3:35 PM Kevin Berlen via <kevin.berlen= [email protected]> wrote: A site I used to maintain had a Class A FM on 105.5, and a 250W FX on 100.5, with the same programming. It was in an industrial area with about 6 low profile 450mHz business repeaters near by. That caused all sorts of problems. We finally proved to two different land-mobile shops that the FM's were clean, as the problem signals didn't exist until their own repeater TX was added into the mix. Of course they were all using mobile style reject only duplexers. I suggested they coordinate non standard repeater pairs, but not sure if that was a viable option for them or not. Have not heard from any of them in several years.
On Thu, Mar 13, 2025 at 12:39 PM, Jim Barbour wrote:
-->Look for another FM station 5 MHz away (88.7 or 98.7)...if there's
none within 15-20 miles, you're probably ok...
Oh Lord....??? many, many years ago a new ham repeater was coordinated on
147.21 at a local MAJOR site.? Nobody knew that there was a paging system
on 152.21...? and that particular system was not very active... But when both
were on the air simultaneously the mix trashed EVERY UHF repeater. (well,
the 470-476? and 506-512 systems were not affected)
?
The public safety people were NOT happy. ? Emphasis on the NOT.?
Neither were the various commercial UHF repeater owners.?
There was no easy solution.? The final fix was that the ham system ended up
running "upside down" (147.21 in, 147.81 out) for the next 30-35 years (until
the 152.21 paging system shut down).
?
Mike WA6ILQ
?
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At 3/13/2025 01:25 PM, you wrote:
On Thu, Mar 13, 2025 at 12:39
PM, Jim Barbour wrote:
- -->Look for another FM station 5 MHz away (88.7 or 98.7)...if
there's
- none within 15-20 miles, you're probably ok...
Oh Lord....??? many, many years ago a new ham
repeater was coordinated on
147.21 at a local MAJOR site.? Nobody knew that there was a paging
system
on 152.21...? and that particular system was not very active... But
when both
were on the air simultaneously the mix trashed EVERY UHF repeater.
(well,
the 470-476? and 506-512 systems were not affected)
?
The public safety people were NOT happy.?? Emphasis on the
NOT.?
Neither were the various commercial UHF repeater owners.?
There was no easy solution.? The final fix was that the ham system
ended up
running "upside down" (147.21 in, 147.81 out) for the next
30-35 years (until
the 152.21 paging system shut down).
Timing was different from how you state Mike: the 2 meter system was
originally on 147.81, then got flipped to 147.21, perhaps to align with
the area bandplan.? I think the paging TX came sometime later,
because the 2A - B mix didn't start with the 81/21 flip.? The paging
TX was not a high power TX as it was meant to fill coverage gaps, not to
provide primary coverage.? The problem remained until the 152.21
paging TX was decommissioned.
Bob NO6B
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At 3/13/2025 02:32 PM, you wrote:
Split antennas and a circulator
would have fixed the problem..
Nope: my 440 system already had separate TX & RX antennas vertically
separated 60'.? Circulators on everything.
The source points of the 2A - B mix were numerous joints throughout the
tower.? Painting them over with conductive paint did reduce the mix
levels to below most RX noise floors for a couple of months, but would
return thereafter.
Bob NO6B
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I've worked at several "high power" sites in the past. I would suggest that you bring a wattmeter and dummy load to the site. Connect the wattmeter with a dummy load to the antenna feedline and you may be amazed at how much power can come down the coax. This power may not cause interference but might cause damage to your equipment.
73, Joe, K1ike
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On 3/13/2025 11:17 AM, Kevin Berlen via groups.io wrote: I had to install a FM trap on the repeater feedline to reduce the amount of RF getting into the system from the FM stations. We have about 250ft vertical separation between the broadcast array and the repeater antenna.
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Pre 1992.. before I left Detroit, one Amateur placed a 440 repeater on the side of an FM tower.. Antenna wise, He installed a pair of 4 (maybe 8) bay stacked dipoles in cardiod pattern? opposite sides of the tower..
Think of it as a cardiod pattern East and a cardiod pattern West.. totally omnidirectional except for a slight theoretical notch in the pattern North and South.
?
It had tremendous coverage, but Detroit is pretty flat..? with elevation variation of only 75 feet in 3-4 counties.
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People have mentioned isolator and circulator any brand better than the other?? ?
?
If I remember correctly.? ?The isolator are used on the TX and RX side of the repeater ports to the duplexer?
?
The circulator is used after it combines on the duplexer output to go up the antenna?
?
Also it was stated to bring a watt meter to look for potential RF energy coming down the cable.? ? I'm assuming you'll want too look for the RF on the repeater frequency or the radio station frequency?? ?What do you do if you find such a issue??
?
Appreciate everyone help on.? Lot's of good information.
?
Thanks
Steven H
N8RLW?
?
?
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Isolators are only used on the tx side. ? An isolator is generally a 3 port circulator where one port is terminated. In some systems, such as radar, a circulator can be used to allow a transmitter and receiver to share the same antenna. It is possible to have more than 3 ports on a circulator ? You typically don’t see a circulator in “LMR.” ? You don’t need to tune into any frequency in particular. As mentioned, simply insert a power meter in the line and put a load on the other port. If you want to measure the level at a given frequency, then you’ll need additional equipment. ? As far as what to do… you can trap/stub it, add band pass filtering, or ignore it (if you have equipment that tolerates it.) Why would we do something about it? Because hams are cheap. BpBr duplexers are used, with the owners not understanding that they really aren’t “band pass” as they think they are. Or, notch only duplexers are used, or crappy rf decks. Insert a lot of reasons. ? An actual band pass filter, given adequate separation (i.e., FM broadcast/2m) can kill “all” the signal/voltage from the broadcast transmitter. Only passing the desired band, i.e., 2m, or even a narrower portion. Alternatively, you can trap the broadcast station, cleaning the line for all the downstream users, then add a band pass too, shielding your receiver from all kinds of unwanted signals. ? Matt AL0R ?
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From: [email protected] <[email protected]> On Behalf Of steven harvey via groups.io
Sent: Friday, March 14, 2025 13:14
To: [email protected]
Subject: Re: [repeater-builder] Running a Repeater on a FM Broadcast Tower ? People have mentioned isolator and circulator any brand better than the other?? ? If I remember correctly.? ?The isolator are used on the TX and RX side of the repeater ports to the duplexer? The circulator is used after it combines on the duplexer output to go up the antenna? Also it was stated to bring a watt meter to look for potential RF energy coming down the cable.? ? I'm assuming you'll want too look for the RF on the repeater frequency or the radio station frequency?? ?What do you do if you find such a issue?? Appreciate everyone help on.? Lot's of good information.
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Circulators are used all the time in LMR...Combiners have them, I've used them on conventional systems where IMD was a problem...never called them isolators in my 50+ years of LMR..
Chris WB5ITT?
Isolators are only used on the tx side. ? An isolator is generally a 3 port circulator where one port is terminated. In some systems, such as radar, a circulator can be used to allow a transmitter and receiver to share the same antenna. It is possible to have more than 3 ports on a circulator ? You typically don’t see a circulator in “LMR.” ? You don’t need to tune into any frequency in particular. As mentioned, simply insert a power meter in the line and put a load on the other port. If you want to measure the level at a given frequency, then you’ll need additional equipment. ? As far as what to do… you can trap/stub it, add band pass filtering, or ignore it (if you have equipment that tolerates it.) Why would we do something about it? Because hams are cheap. BpBr duplexers are used, with the owners not understanding that they really aren’t “band pass” as they think they are. Or, notch only duplexers are used, or crappy rf decks. Insert a lot of reasons. ? An actual band pass filter, given adequate separation (i.e., FM broadcast/2m) can kill “all” the signal/voltage from the broadcast transmitter. Only passing the desired band, i.e., 2m, or even a narrower portion. Alternatively, you can trap the broadcast station, cleaning the line for all the downstream users, then add a band pass too, shielding your receiver from all kinds of unwanted signals. ? Matt AL0R ? From: [email protected] <[email protected]> On Behalf Of steven harvey via
Sent: Friday, March 14, 2025 13:14
To: [email protected]
Subject: Re: [repeater-builder] Running a Repeater on a FM Broadcast Tower ? People have mentioned isolator and circulator any brand better than the other?? ? If I remember correctly.? ?The isolator are used on the TX and RX side of the repeater ports to the duplexer? The circulator is used after it combines on the duplexer output to go up the antenna? Also it was stated to bring a watt meter to look for potential RF energy coming down the cable.? ? I'm assuming you'll want too look for the RF on the repeater frequency or the radio station frequency?? ?What do you do if you find such a issue?? Appreciate everyone help on.? Lot's of good information.
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- Circulators are used all the time in LMR...Combiners have them, I've used them on conventional systems where IMD was a problem...never called them isolators in my 50+ years of LMR..
? A circulator becomes an isolator when only two ports are passing the desired RF and the third port is terminated in a reject load.? Or to say it another way, a circulator is one of two components required to make an isolator.? Isolators only allow RF to flow between two adjacent ports, the third port being a dead end. ? Circulators which are not in isolator service are often used for transmit/receive RF steering such as in microwave waveguide branching networks.? The circulators are oriented such that, for transmitters, RF flows from a given transmitter toward the antenna, and oriented the other way so RF flows from the antenna toward a given receiver, with transmitters and receivers each having single-channel waveguide filters in-line between the radio and the circulator.? Each filter presents a poor match to any/all other frequencies other than the channel they are tuned for, thus keeping off-channel RF flowing around the circulator until it reaches the intended port (either up the stack toward the antenna for transmitters, or down the stack toward receivers or the final termination at the bottom). ? ??????????????? ??????????????????????????????????????????????????????????????????????????????? --- Jeff WN3A
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Chris Boone WB5ITT
Larry Macionski