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Author Topic: Best Repeater Config  (Read 9621 times)
KC2YU
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Posts: 74




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« Reply #30 on: December 17, 2014, 06:11:57 AM »


I will look into those products as well as circulators.

Thanks again!

Comprod Communications - 406-512 MHz 8dB Quad 1/4 Wave Dipole

This is a 4-bay quasi omni with an advertised gain of about 8db.  It's just over 10 feet long.  It's about $900 to $1000. 

Comprod Communications - 406-512 MHz 5dB Dual 1/4 Wave Dipole

This is a 2-bay with about 5 db gain.  It's about 86 inches and sells for about #600 to $700.

ALso keep in mind that the stated frequency range of these antennas is not as wide as stated.  These models cover 406-512 but only in 10mHz ranges.  In otherwords, you need to order the band split you need.  While a 450-460 antenna will look ok SWR wise in the 440 ham band, you probably won't like the pattern.  So, if buying a used antenna, make sure it's made for the frequency you intend to use it for.

There are many many others out there.  I have never used a Comprod so I can't give any first hand data as to how it performs or how rugged it is, but it is marketed to commercial communications companies.

As for the circulator, your internal duplexer is likely just bolted into the chassis and is connected with either BNC or N connectors.  The circulator probably won't fit inside the cabinet.  The repeater configuration you describe isn't intended for the type of installation you describe.  It's more for small footprint low RF environment.  These are typically used for places like construction sites, facilities for in-buiilding comms, campuses, etc.  For use in high RF places you would want a pass-notch duplexer or pass only duplexer.  But, try what you have and see how it works out.


I would suggest extensive reading on repeater-builder.com..







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NJ1K
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Posts: 369




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« Reply #31 on: December 17, 2014, 07:51:27 AM »

Just for a clarification, for a notch-only duplexer like you will have, it simply notches out one exact frequency (actually two).  For example, the TX side ONLY notches out your receive frequency but passes ALL other frequencies.  Likewise, the RX side ONLY notches your TX frequency but allows ALL others to pass.  Thousands of other frequencies will pass right through your duplexer and into your receiver and transmitter.  These will all be varying signal strength and some will be there all the time (think broadcast stations) and some will only be there intermittently (think two-way radio systems). 

These signals will mix in your transmitter and receiver.  On the transmit side, the byproducts of all the mixing will go back up your feedline and re-radiate on "who knows what" frequencies.  Thus strong potential for interference to others.  On the receive side, mixing in your receiver will cause unpredictable operation of your receiver.  These problems can show up as a deaf RX, noisy RX, uncontrolled keying of your TX, etc. 


A  pass-notch provides a pass frequency, and a notch frequency (pass the RX and notch the TX on the RX side and vice versa on the TX side).  All other frequencies will be attenuated to some degree, but each frequency attenuation will vary.  SO, some undesired frequencies will still make it through.

A pass only provides a pass ONLY on the frequencies you need.  The TX side ONLY allows your TX frequency to pass while heavily attenuating ALLL other frequencies and vice versa on the RX side. 

Pass only usually have more insertion loss and are more expensive.  Pass-notch will have a lower insertion loss but sometimes can't keep out problem frequencies.  While you might get by with a notch-only combined with a circulator, just adding the circulator isn't a magic bullet to eleminate all interfference.

Further, it is possible and actually even likely your system will cause some level of interference to other systems both in the ham band as well as other services without even knowing it.  The victims will take a long time (even years in some cases) to locate the root cause of that interference.  And it will end up being a combination of offenders, you included.

So, the bottom line is this:  If your repeater is located in an area where there are lots of transmitters around it (even 5 miles away or more), on any frequency (not just ham bands), your best mitigation of interference both to them and you is to use only the best (expensive) radios, duplexer and circulator.  While it is remotely possible that cheap stuff can work without causing interference, it seldom works out that way.

My repeater is out in the country with few transmitters in sight however, within a mile radius there is likely 100 other transmitters.  Within 5 miles there are likely another 200 to 300 more.  On 2- meters I use a pass-notch 4-can duplexer without a circulator and as far as I know, I have no angry neighbors.  That said though, I do occasionally get a little desense on the RX.  It's been so intermittent that I haven't been able to even start to find it.  Anyway, just food for thought.  Good luck with your project.  Full duplex operation is very complex.  There is a whole world of knowledge out there to learn about repeaters.  Keep reading and then read some more.

Oh one more thing:  My repeater has been on the air for about 9 years now.  Not counting site rental, I have spent about $10,000 installing, maintaining and repairing.  It's a money pit for sure.  But it also returns an educational value.
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KJ4I
Member

Posts: 115




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« Reply #32 on: Yesterday at 10:35:30 PM »

Quote
The site is the top of a building.  While I have permission, the owner is sensitive to how the antenna looks and the size, etc.  (There are no other antennas on the roof.)  I was considering a Diamond X50 (not too tall, great reputation and dual band so I could switch without changing antennas).

I am also leaning towards a Bridgecom BCR-40U for the repeater with duplexer built in.

I haven't thoroughly read all of the follow up reviews but think some have suggested a commercial antenna as the best option. I would agree 110% and wouldn't even bother with something like a Diamond X50 for repeater use. They are ok for a home base station but a repeater is a whole different animal and performance will suffer greatly. Especially trying to run a dual band antenna on a repeater. IT's just not optimal at all. I know from first hand experience.

As far as the Bridgecom. That is a great repeater. I have the VHF version and it has a very good receiver and the audio reproduction is wonderful. Keep in mind, it is a commercial repeater and the built in controller is pretty basic. It is pretty finicky to program without much explanation as to what a lot of the settings actually do because they are designed for commercial users. I just had to figure the programming out by trial and error. It is much easier with the software. If you don't have everything set just right the controller wont take the programming. If your planning on going with another controller such as an Arcom or S-Com then it might be a moot point. I had an Arcom years ago and liked it a lot. I recently thought about putting an S-Com on my repeater but decided I just like the simplicity of the native controller and really don't need all those extra ports and functions anymore. I don't really have much interest in having tons of controller functionality these days unlike in the past. As long as it repeats and ID's im good to go.
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