Thoughts on this one?
Dual 100W Circulator Isolator 453 480 MHz Minimum 50 DB Isolation with 60W Load | eBay
Dual 100W Circulator Isolator 453 480 MHz Minimum 50 DB Isolation with 60W Load | eBay
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UHF Repeater Antenna Spacing Question
- Thread starter Cowley639
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freddaniel
Member
This is a fine circulator with at least 50 dB isolation, and an attached load. The only thing unusual is the 1st load is designed to be attached to a metal surface, to dissipate the heat, should the antenna fail, all the transmitter power would be reflected to this load.
If you run 50 watts, a cabinet wall or a small 4" x 4" heatsink would work fine. This allows you to be creative. Many people have found loads at half the transmitter power work OK, as it is rare for the antenna to fail 100% and there is typically loss in the feedline to the antenna.
If you run 50 watts, a cabinet wall or a small 4" x 4" heatsink would work fine. This allows you to be creative. Many people have found loads at half the transmitter power work OK, as it is rare for the antenna to fail 100% and there is typically loss in the feedline to the antenna.
Great,
The repeater system is all being mounted in a 20RU space equipment rack. It is fairly large rack, could I just mount it to the rack side wall?
Also will the School's repeater need the same circulator isolator on it as well?
The repeater system is all being mounted in a 20RU space equipment rack. It is fairly large rack, could I just mount it to the rack side wall?
Also will the School's repeater need the same circulator isolator on it as well?
Also I was able to determine I will be able to get about 20ft of horizontal seperation between the two antennas
freddaniel
Member
YES, both repeaters will require circulators to prevent intermod.
Do they need to be tuned to the specific frequency both repeaters are using? Also I have heard a few people talk about putting a low pass filter on the antenna side of the circulator.
Thoughts?
Thoughts?
Any advantage to this one over the cheaper one?
Celwave CD460 A 450 470 MHz 100 Watt Dual Isolator Circulator with Two 15W Loads | eBay
Celwave CD460 A 450 470 MHz 100 Watt Dual Isolator Circulator with Two 15W Loads | eBay
freddaniel
Member
Circulators used in UHF two-way radio are broadband devices and will always cover about 20 to 30 MHz without tuning, at a minimum specification of 25 dB for a single junction and 50 dB for a dual junction unit. Therefore, they do not require field tuning to a specific frequency. The actual frequency tuning is done by increasing or decreasing the magnetic field of the internal magnet used to bias the junction, at the time of manufacturer. This requires a special machine with a RF network analyzer attached to center the operating frequency near the desired or nameplate frequency. This is why it is not recommended to mount a circulator against a metal surface like mild steel, as this may alter the magnetic field and therefore the actual operating frequency range.
The typical 50 dB isolation, plus the approximate 35 dB isolation between antennas [85 dB total] will almost always be enough [98%] to suppress any intermod [inter-modulation products] from occurring.
However, there are some circulators built [like the one you asked about] with trimmer piston caps at each port to match the impedance of the connection more precisely at your specific operating frequency, thereby improving the return isolation from 50 dB to as much as 80 dB. This adjustment is rarely required, unless (1) you are a "purest" seeking every dB available; or (2) your antenna isolation is less and you require more total isolation to prevent a particular intermod mix from occurring [2%].
The use of a filter on the circulator output is always recommended as the typical circulator is not a perfect device and is sometimes non-linear. This non-linearity in certain cases could cause intermod, so a low-pass filter; or a second harmonic notch filter; or a simple cavity will suffice to eliminate this possibility.
Keep in mind the only difference between a commercial transmitter combiner, v.s. a circulator & cavity is a simple jumper cable and "star" connection, for connecting to ONE antenna. This is why some commenters have suggested switching to a receiver combiner and a transmit combiner.
In your case, with the two transmitters 225 KHz apart, you would need to use a hybrid coupler to combine the two circulators, with a single filter on the output. The hybrid would cost you 3 dB loss of both transmitters output, due to the close spacing. If the transmit frequencies were 1 MHz or more apart, then just the cavities would be used.
I hope this answer is complete
The typical 50 dB isolation, plus the approximate 35 dB isolation between antennas [85 dB total] will almost always be enough [98%] to suppress any intermod [inter-modulation products] from occurring.
However, there are some circulators built [like the one you asked about] with trimmer piston caps at each port to match the impedance of the connection more precisely at your specific operating frequency, thereby improving the return isolation from 50 dB to as much as 80 dB. This adjustment is rarely required, unless (1) you are a "purest" seeking every dB available; or (2) your antenna isolation is less and you require more total isolation to prevent a particular intermod mix from occurring [2%].
The use of a filter on the circulator output is always recommended as the typical circulator is not a perfect device and is sometimes non-linear. This non-linearity in certain cases could cause intermod, so a low-pass filter; or a second harmonic notch filter; or a simple cavity will suffice to eliminate this possibility.
Keep in mind the only difference between a commercial transmitter combiner, v.s. a circulator & cavity is a simple jumper cable and "star" connection, for connecting to ONE antenna. This is why some commenters have suggested switching to a receiver combiner and a transmit combiner.
In your case, with the two transmitters 225 KHz apart, you would need to use a hybrid coupler to combine the two circulators, with a single filter on the output. The hybrid would cost you 3 dB loss of both transmitters output, due to the close spacing. If the transmit frequencies were 1 MHz or more apart, then just the cavities would be used.
I hope this answer is complete
After reading your comments it sounds like It would make more sense for me to just leave my repeater on GMRS (which it is currently programmed to) which would increase the frequency separation to 1.725 MHz apart.
The reason we were looking to get a business itinerant license was for use when we (as a company) travel to different work sites around the area. I was just going to set-up the repeater i have on GMRS now (and tune it to one of the itinerant frequencies) because I had a repeater to use it on. The range I am getting on the repeater now at our offices are not sufficient. Furthermore, we are moving our offices soon and I will no longer be able to keep my repeater up at it's current location, which is why I contacted the school about putting it up on the gym building.
So with that said, let me confirm I am understanding this correctly;
Repeater 1 - (School Repeater)
464/469.325
Vertex VXR9000 Repeater - 50w output
Mobile Duplexer
1/2 Heliax
Hutstler 6dB antenna
Repeater 2 - (My Repeater)
462/467.600
Icom FR4000 Repeater - 50w output
DB4076 Duplexer
1/2 heliax
Comet CA-712EFC 9dB antenna
Both repeater antennas will be separated horizontally by aprox 20-25 feet. Both Repeaters will need a circulator/isolator (Dual 100W Circulator Isolator 453 480 MHz Minimum 50 DB Isolation with 60W Load | eBay) and a low-pass filter between the transmitter output and the duplexer of each repeater.
I found the circulator/isolators for sale on eBay, but I still need to find a low-pass filter for each repeater. Any suggestions?
The reason we were looking to get a business itinerant license was for use when we (as a company) travel to different work sites around the area. I was just going to set-up the repeater i have on GMRS now (and tune it to one of the itinerant frequencies) because I had a repeater to use it on. The range I am getting on the repeater now at our offices are not sufficient. Furthermore, we are moving our offices soon and I will no longer be able to keep my repeater up at it's current location, which is why I contacted the school about putting it up on the gym building.
So with that said, let me confirm I am understanding this correctly;
Repeater 1 - (School Repeater)
464/469.325
Vertex VXR9000 Repeater - 50w output
Mobile Duplexer
1/2 Heliax
Hutstler 6dB antenna
Repeater 2 - (My Repeater)
462/467.600
Icom FR4000 Repeater - 50w output
DB4076 Duplexer
1/2 heliax
Comet CA-712EFC 9dB antenna
Both repeater antennas will be separated horizontally by aprox 20-25 feet. Both Repeaters will need a circulator/isolator (Dual 100W Circulator Isolator 453 480 MHz Minimum 50 DB Isolation with 60W Load | eBay) and a low-pass filter between the transmitter output and the duplexer of each repeater.
I found the circulator/isolators for sale on eBay, but I still need to find a low-pass filter for each repeater. Any suggestions?
freddaniel
Member
The used UHF low pass filter is maybe the hardest thing to source. That is why I suggested either a second harmonic notch filter, or a UHF cavity. Neither of these are available now on Ebay at a reasonable price. However, there are two low pass filters available for sale on Ebay, under item 222104740276 but the listing also contains a single junction UHF Circulator and a UHF Hybrid coupler. You must satisfy yourself the description is correct. The seller is willing to take offers, so offer to purchase just what you want. The value of each piece is:
Low pass filters - $50 each
Hybrid Coupler - $50
UHF Circulator - $150
Now, the more important issue. If you change your frequency to 462.600, you risk your receiver being overloaded by the school transmitter now only 3.775 MHz away. Before at 225 KHz apart, you were still getting a great deal of protection from your notch duplexer. This was the first consideration at the beginning of the thread.
Even with the repeater antennas being 25 ft apart, you will still be faced with 35 dB coupling between antennas, which will dump more than 10 mw [+10 dBm] into your receiver. This needs to be attenuated at least 70 dB to prevent overload of your receiver.
Even if you can put up with the overload, then the transmitter broadband noise from the school transmitter will get you. This noise usually starts at -80 dB under their carrier, and declines with frequency separation from the school carrier. Lets say it works out the noise at your receive frequency is measured at -100 dB down, then the on-channel noise into your receiver would be at -90 dBm, or 2.24 uV, which would cause substantial interference.
Both of the above problems can be resolved with several additional notch filters. Again, from the start of the thread, many commenters suggested either better duplexers or converting to multicoulped transmit and receive systems. As you can see, even with just two repeaters, it is sometimes difficult to operate both at full specification.
In order of consideration when placing new repeater at same location of one or more existing repeaters: your receiver overload - broadband noise on your receiver [from your Tx and others] - intermod caused by your transmitter mixing with other transmitters nearby -
Low pass filters - $50 each
Hybrid Coupler - $50
UHF Circulator - $150
Now, the more important issue. If you change your frequency to 462.600, you risk your receiver being overloaded by the school transmitter now only 3.775 MHz away. Before at 225 KHz apart, you were still getting a great deal of protection from your notch duplexer. This was the first consideration at the beginning of the thread.
Even with the repeater antennas being 25 ft apart, you will still be faced with 35 dB coupling between antennas, which will dump more than 10 mw [+10 dBm] into your receiver. This needs to be attenuated at least 70 dB to prevent overload of your receiver.
Even if you can put up with the overload, then the transmitter broadband noise from the school transmitter will get you. This noise usually starts at -80 dB under their carrier, and declines with frequency separation from the school carrier. Lets say it works out the noise at your receive frequency is measured at -100 dB down, then the on-channel noise into your receiver would be at -90 dBm, or 2.24 uV, which would cause substantial interference.
Both of the above problems can be resolved with several additional notch filters. Again, from the start of the thread, many commenters suggested either better duplexers or converting to multicoulped transmit and receive systems. As you can see, even with just two repeaters, it is sometimes difficult to operate both at full specification.
In order of consideration when placing new repeater at same location of one or more existing repeaters: your receiver overload - broadband noise on your receiver [from your Tx and others] - intermod caused by your transmitter mixing with other transmitters nearby -
So what your saying is; I would actually be better off using the 464/469.550 frequency pair instead of the 462/467.600 GMRS pair?
I hadn't taken into consideration that my duplexer would help with protecting the repeaters from each other.
I also want to reiterate, the school's repeater gets used very, very, very little. I've been monitoring the frequency for about a month now, and I can count on one hand the number of times I have heard someone using it. So it's not like its being used in continuous duty. My repeater would be used quite a bit more than the school's but again nothing continuous.
To make a long story short, my company is a contractor for the school, we manage all the sound and video equipment on campus. We have a bunch of equipment in the gym building which made it a good candidate for the repeater site. We have access to the building at all times so if anything happened we could get right to it. The repeater would be mounted in a rack inside a room that is right beside a room that houses a lot of our other equipment. (About 30ft down the hallway from the school's repeater) In total about 70ft of coax to the repeater from the antenna.
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I hadn't taken into consideration that my duplexer would help with protecting the repeaters from each other.
I also want to reiterate, the school's repeater gets used very, very, very little. I've been monitoring the frequency for about a month now, and I can count on one hand the number of times I have heard someone using it. So it's not like its being used in continuous duty. My repeater would be used quite a bit more than the school's but again nothing continuous.
To make a long story short, my company is a contractor for the school, we manage all the sound and video equipment on campus. We have a bunch of equipment in the gym building which made it a good candidate for the repeater site. We have access to the building at all times so if anything happened we could get right to it. The repeater would be mounted in a rack inside a room that is right beside a room that houses a lot of our other equipment. (About 30ft down the hallway from the school's repeater) In total about 70ft of coax to the repeater from the antenna.
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freddaniel
Member
YES, you would actually be better off using the 464/469.550 frequency pair, and probably use a different PL tone.
It has been my experience you want to protect the school repeater at all cost, regardless of the duty cycle of their repeater. Should you cause interference to their operations, they might want to review all of their relationships with your company.
Good luck
It has been my experience you want to protect the school repeater at all cost, regardless of the duty cycle of their repeater. Should you cause interference to their operations, they might want to review all of their relationships with your company.
Good luck
freddaniel
Member
Your drawings are correct, and well done.
The issue of earth grounding of the antennas is also important. Even though it is possible, but unlikely, you will sustain a direct lightning strike, you will eventually receive a SECONDARY strike. At the very least, you should place a 5/8" x 8 ft copper coated ground rod and extend a #2 tinned copper wire to both antennas. Some people also place a Polyphaser lightning arrestor, where the Heliax enters the building, tied to the ground system. Others simply use a Heliax compression ground kit.
Since you are using a steel cabinet, I would suggest connecting the Heliax directly to a polyphaser mounted on the outside wall or top of the cabinet. Once inside the cabinet, you can use RG214 to the duplexer and other connections. I would also suggest routing the power cord through a "Corcom Power Line Filter" mounted on the exterior of the cabinet, near where the polyphaser is located. These look like a computer power cord input. These are available on Ebay for under $8 and be sure to buy a spare.
The idea is to "encapsulate" your repeater and power supply in steel, so that any lightning surge will not reach your equipment. The idea of the power line filter is to protect your power supply, as the AC power cord or power line filter will fail before damaging the AC supply. Any other cables entering the cabinet [ethernet?] should also pass through some form of protection.
As an added bit of protection, add a 120 VAC surge suppressor on the inside of the cabinet between the power line filter and your 12vdc power supply. To avoid trips to the site to reset the power supply from a voltage spike, use a auto-reset power supply that has a wide auto-ranging 100 to 240VAC input.
The issue of earth grounding of the antennas is also important. Even though it is possible, but unlikely, you will sustain a direct lightning strike, you will eventually receive a SECONDARY strike. At the very least, you should place a 5/8" x 8 ft copper coated ground rod and extend a #2 tinned copper wire to both antennas. Some people also place a Polyphaser lightning arrestor, where the Heliax enters the building, tied to the ground system. Others simply use a Heliax compression ground kit.
Since you are using a steel cabinet, I would suggest connecting the Heliax directly to a polyphaser mounted on the outside wall or top of the cabinet. Once inside the cabinet, you can use RG214 to the duplexer and other connections. I would also suggest routing the power cord through a "Corcom Power Line Filter" mounted on the exterior of the cabinet, near where the polyphaser is located. These look like a computer power cord input. These are available on Ebay for under $8 and be sure to buy a spare.
The idea is to "encapsulate" your repeater and power supply in steel, so that any lightning surge will not reach your equipment. The idea of the power line filter is to protect your power supply, as the AC power cord or power line filter will fail before damaging the AC supply. Any other cables entering the cabinet [ethernet?] should also pass through some form of protection.
As an added bit of protection, add a 120 VAC surge suppressor on the inside of the cabinet between the power line filter and your 12vdc power supply. To avoid trips to the site to reset the power supply from a voltage spike, use a auto-reset power supply that has a wide auto-ranging 100 to 240VAC input.
I had definitely planned on a lightning system.
The school's repeater has a ground compression kit (where it enters the building)units; and a polyphaser mounted to the metal shelf in the closet where the repeater is located, it is then grounded to the building electrical ground system.
I had planned to do the same, since the heliax enters the building at the same location, in terms of power for the repeater. The FR4000 has an internal PS, and the room where the repeater will be located has surge protectors.
Sent from my iPhone using Tapatalk
The school's repeater has a ground compression kit (where it enters the building)units; and a polyphaser mounted to the metal shelf in the closet where the repeater is located, it is then grounded to the building electrical ground system.
I had planned to do the same, since the heliax enters the building at the same location, in terms of power for the repeater. The FR4000 has an internal PS, and the room where the repeater will be located has surge protectors.
Sent from my iPhone using Tapatalk
UHF Tunable Notch Filter Cavity Ham GMRS for Repeater for Extra RCVR Isolation | eBay
Any advantage to a Notch filter on the RX side of the system? Would it be beneficial to have it tuned to notch out the RX signal of the Schools repeater (469.3250)?
If this would help, would it need to be placed on the antenna side or radio side of the duplexer?
Any advantage to a Notch filter on the RX side of the system? Would it be beneficial to have it tuned to notch out the RX signal of the Schools repeater (469.3250)?
If this would help, would it need to be placed on the antenna side or radio side of the duplexer?
Last edited:
kayn1n32008
ØÆSØ Say it, say 'ENCRYPTION'
It could be, it would go between the duplexer and the repeater. I believe the jumper between the notch filter and the duplexer would also need to be a non-even multiple 1/4wave length.
What approximate length of coax would that be?
kayn1n32008
ØÆSØ Say it, say 'ENCRYPTION'
Depends. You would need to calculate the 1/4 wave length at your frequency, then adjust it for the coax jumper velocity factor, then multiply by 1, 3, 5, 7 or 9 depending on how long you need it.
Another question;
I am using RG214 for my in-cabinet jumpers. I am needing a little bit longer length for one of my cables. I have an RG213 jumper that I didn't realize that I had, fortunately it is the correct length for what I am needing.
My question is; Is RG213 okay on the RX side between the Duplexer and the Repeater? I am using RG214 on the TX Side between the Repeater, Isolator and Duplexers.
I am using RG214 for my in-cabinet jumpers. I am needing a little bit longer length for one of my cables. I have an RG213 jumper that I didn't realize that I had, fortunately it is the correct length for what I am needing.
My question is; Is RG213 okay on the RX side between the Duplexer and the Repeater? I am using RG214 on the TX Side between the Repeater, Isolator and Duplexers.
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