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Commercial Radio Antennas - Please keep discussion related to professional, commercially used antennas and antenna systems for the two-way radio industry. Topics for the use of these antennas on amateur bands are accepted here.

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  #1 (permalink)  
Old 06-07-2017, 12:36 PM
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Default VHF repeater help

I'm trying to put a repeater up and cannot get any distance out of it. Does the length of coax from duplexer to radio have any influence on the system also not sure if I have a good grade antenna so any help will be greatly appreciated
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Old 06-07-2017, 4:07 PM
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Working with repeaters can be a tough row to hoe. There are lots of potential problem areas but, in my view, there are three things that are essential...

- As they say in real estate... location! location! location! A good location is one with height and prominence. A ten foot pole on the garage probably won't cut the mustard;

- A high-quality (commercial) antenna - Many repeater owners say that the folded dipole types work best for repeaters (think DB-224);

- A high-quality BpBr duplexer and a high-quality, low-loss feedline - Cable loss and receiver desense (from the transmitter) can kill the performance of the best repeater stations.

If you can provide more detail, perhaps others might offer some more specific suggestions. Best of luck!

John AC4JK
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Old 06-07-2017, 4:32 PM
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We need way more info from the OP before any suggestions can be made.

Repeaters are not for the faint of heart!
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Old 06-07-2017, 5:27 PM
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I have a Ken wood vhf and a Chinese brand duplexer with a fiberglass antenna not sure the brand but it sounds like it may be way over my head since I know nothing about the in and outs of this
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Old 06-07-2017, 6:05 PM
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To help us help you, please answer the following:

1) What brand, type, and length of feedline do you use between the antenna and duplexer?

2) What height is your antenna?

3) What make (Kenwood), model, and power output is your repeater?

4) What specific duplexer are you using (make, model, and any other specs you have available)?

5) What make, model, and other specs for your antenna?

6) What brand, type, and length of jumper is between your repeater and duplexer?

7) What type of location is your repeater in (home, commerical building, commercial tower, etc.) and include specifics on if you're the only station at that location or if others share it (include details on them if known)?

8) What type and brand connectors are on your setup? Include any adapters that may be used as well please.

9) Please include any other details you have about your setup, even if they don't seam important to you (they may be the key!).
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Old 06-07-2017, 6:08 PM
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What is your frequency pair or the spacing between tx and rx? The small flatpack VHF duplexers around 6" X 8" X 1" are rated for a 5MHz minimum split which is wider than the 2m band. For a 1MHz split you usually need a large 4 cavity duplexer with minimum 4" dia cavities that's about 2ft tall and preferably a pass/notch type. For a 600KHz split you really need a 6 cavity model.

New they run at least $1k on up for a 4 cavity and upwards of twice that for a good 6 cavity. You can find used ones much cheaper but they are still hundreds of $$ if in good shape and tunable across the 2m amateur band.
prcguy

Quote:
Originally Posted by Semofarmer View Post
I have a Ken wood vhf and a Chinese brand duplexer with a fiberglass antenna not sure the brand but it sounds like it may be way over my head since I know nothing about the in and outs of this
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Old 06-07-2017, 7:47 PM
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Feedline is about 60' of rg58
Antenna is about 30'
Kenwiod tkr 750
The jumpers are different lengths one is about 24" and one is 16"
Antenna is a fiberglass about 4' in length but model is unknown
And connectors are a assortment of types
And it is located in my home for a farm king operation
I know this is pretty vague so any info will be helpful
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Old 06-07-2017, 9:48 PM
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60' of RG-58 on a VHF repeater is a problem but not your main problem. In my experience unless you have tuned or checked the duplexer at the place its installed, it's probably been detuned in shipping and handling and will cause lots of problems. That assumes the duplexer is adequate for your frequency spacing and transmit power.

It takes a lot of knowledge and test equipment to put a repeater system together and install it correctly. When something doesn't work as in your case, there is no way to determine what the problem is and no equipment to make adjustments or measure how well the repeater and duplexer is working.

I'm not going to offer any suggestions except for having someone familiar with setting up repeaters and with proper test equipment to diagnose your problem on site. Anything else is a complete wast of time.
prcguy


Quote:
Originally Posted by Semofarmer View Post
Feedline is about 60' of rg58
Antenna is about 30'
Kenwiod tkr 750
The jumpers are different lengths one is about 24" and one is 16"
Antenna is a fiberglass about 4' in length but model is unknown
And connectors are a assortment of types
And it is located in my home for a farm king operation
I know this is pretty vague so any info will be helpful
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Old 06-07-2017, 10:02 PM
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Quote:
Originally Posted by prcguy View Post

I'm not going to offer any suggestions except for having someone familiar with setting up repeaters and with proper test equipment to diagnose your problem on site. Anything else is a complete wast of time.
prcguy
Agreed. He needs the help of a reputable two way radio vendor.
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Old 06-09-2017, 11:42 AM
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The Tkr750 is a fine repeater so that's a good start

The feed line should be LMR400 at a minimum

Duplexer jumpers should be RG400 or equivalent and length from duplexer to repeater is not critical

I've yet to see a Chinese duplexer I would trust and it's tuning must be done via a tracking generator and an experienced radio tech

If you have a mistuned, mis installed, or defective duplexer it could damage the repeater so having a professional access the system is
important
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Old 06-10-2017, 3:32 AM
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I built a UHF repeater for the in-laws ranch operations a few years back & it has really helped them out. If you're setting this up for ag, see if you can find a local two way shop or even a local ham club that owns & maintains repeaters. They should be able to get you set up, or at least tell you what you're going to need.

Gonna be straight up with you. If you want this to work and work well, you're gonna have quite a bit of funds tied up in it. But once it's up and running it should last many, many years.

The TKR-750 is a great repeater.
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Old 06-10-2017, 4:45 AM
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Yes that's what I'm gonna use it for. Thanks for the advice and I'm not sure how to located any local ham guys is there a website to do that
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Old 06-10-2017, 5:27 AM
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This may be a silly question, but when you ordered the duplexer, they did actually tune it for you? Normally they email you and ask you to supply the input and output frequency. If they did not do this, then it cannot be tuned. A 4ft fibreglass antenna suggests a zero gain design. One thing that is country specific. Here in the UK, to get the licence you have to supply OFCOM, our Government Agency with location, height, power at the antenna, antenna gain and other details to get a licence - did you not have to do the same thing? 60ft of RG58 and a 0dB gain antenna mean that you're losing a not tiny amount in the cable.

A few things you can test. With the duplexer in and out of circuit, inhibit repeat on the Kenwood and just see what the range OUT is. Even with 58, 30 ft up in the air should give reasonable coverage of the terrain is reasonably flat. If you can use cell phones, transmit on the system and see how far it reaches. Then, again with and without the duplexer, try the reverse - inhibit TX, and see what you can hear. If these tow tests give pretty good range, that simply vanishes when you switch to repeat, then it's desense - with the TX output desensitising the receiver - badly tuned duplexer being the normal cause. Report back.
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Old 06-10-2017, 6:38 AM
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What should be done
1. DB224 antenna $1000 ballpark
2. Andrews 7/8 hardline $7 per foot plus $25 per connector
3. Duplexers tuned by radio shop preferred onsite tuning on your antenna system
4. 60 feet will only give you less than 10 miles walkie talkie coverage I would like 150 feet or better.
5. System tuned onsite by a twoway shop tech.
6. Did you get a FCC license for the pair of frequencies you are using? What height is your license for? One last question what power is your license for?
7. New 6 cavity band pass band reject duplexers $1000 ballpark (not ebay mobile duplexers).
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Old 06-10-2017, 7:55 AM
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buddrousa - you forgot the tower, the two trucks of concrete, and the half container for the repeater to sit in, and no mention of backup generator, and UPS.

I must say - joking apart a VHF 4-stack is a little over the top here, isn't it?
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Old 06-10-2017, 8:27 AM
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Quote:
Originally Posted by prcguy View Post
What is your frequency pair or the spacing between tx and rx? The small flatpack VHF duplexers around 6" X 8" X 1" are rated for a 5MHz minimum split which is wider than the 2m band. For a 1MHz split you usually need a large 4 cavity duplexer with minimum 4" dia cavities that's about 2ft tall and preferably a pass/notch type. For a 600KHz split you really need a 6 cavity model.

New they run at least $1k on up for a 4 cavity and upwards of twice that for a good 6 cavity. You can find used ones much cheaper but they are still hundreds of $$ if in good shape and tunable across the 2m amateur band.
prcguy
EPCOM's VHF flat pack is rated at a 4.5 MHz split but will handle 4.4 MHz. Don't see flat packs manufactured in North America that can handle much narrower. I know the Chinese (Jensen) advertise a 3.5 MHz split flat pack but I've never ordered one.

What hasn't been asked is what frequencies is the repeater operating on currently?

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Old 06-10-2017, 9:04 AM
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Sinclair makes a 3.5MHz mobile duplexer.

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Old 06-10-2017, 12:09 PM
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It was not overkill when I was installing VHF farm repeaters where a 20 to 30 mile radius or bigger area was expected. I have put 60 foot ROHN 25G on top of a grain leg and got about 30 miles walkie to walkie coverage. So no I think this setup is about average for a farm operation.
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Old 06-10-2017, 12:14 PM
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Sorry - I thought you were just joking. I got the impression he was a novice installing something on the cheap, with bodge up bits and a small budget - rather than a commercial quality install? The bits and pieces he has would cost around £500 here, so I assumed a somewhat lower level of performance, but not zero performance which is what he's getting. One of mine manages between 5 and 8 miles on handhelds in this part of the UK, and the required range submitted to the authorities was 5 miles as a service area - and they put a limit of 5W on my 3dBd antenna, at 10m agl.
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Old 06-10-2017, 12:40 PM
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Quote:
Originally Posted by paulears View Post
Sorry - I thought you were just joking. I got the impression he was a novice installing something on the cheap, with bodge up bits and a small budget - rather than a commercial quality install? The bits and pieces he has would cost around £500 here, so I assumed a somewhat lower level of performance, but not zero performance which is what he's getting. One of mine manages between 5 and 8 miles on handhelds in this part of the UK, and the required range submitted to the authorities was 5 miles as a service area - and they put a limit of 5W on my 3dBd antenna, at 10m agl.


I have the original sales receipt for one of my Micors. $14,000 in 1982 for a Micor (88W out of the duplexer. For a family sustenance farm…it's overkill but for a commercial farming operation (several thousand to ten thousand acres) it's needed.


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