Multiple Repeaters w/ 1 antenna?

KC2NNS · Post by **KC2NNS** » Mon Apr 09, 2007 1:04 pm

This may sound like a silly or novice questione to some, but.....

Is it possible to have more than one repeater operating on a single antenna by using multiple duplexers?

Thanks in advance.

Bruce1807 · Post by **Bruce1807** » Mon Apr 09, 2007 1:11 pm

I guess technically you could do it with some coupling , however this would not be a substitute for combining.

provide the tx/rx frequencies for the repeaters.

RKG · Post by **RKG** » Mon Apr 09, 2007 5:05 pm

This is not uncommon in some public safety installations, but (a) it is hugely costly and (b) there are some hefty insertion loss issues to deal with. As a result, you need a situation where there are budgets sufficient to cover the engineering, procurement and installation costs.

All of the installations I am familiar with use resonant equipment from Tx/Rx.

wb4bli · Post by **wb4bli** » Mon Apr 09, 2007 5:40 pm

What you need is an RF combiner. We have one we use at our repeater site. It runs a commercial VHF and a HAM VHF. Works well. There is a lot of loss though. They usually run in the several thousands for one. You also need to make sure it will tune to the desired frequecies as some will not.

RKG · Post by **RKG** » Tue Apr 10, 2007 6:56 am

The Tx/Rx equipment I'm familiar with aggregates combiner, multicoupler and duplexer functionality in one tall and expensive stack of cans and related modules. See http://www.txrx.com/product/product_vie ... 4616B6CEEC

440roadrunner · Post by **440roadrunner** » Tue Apr 10, 2007 11:39 am

As said above, this is costly, and can introduce complications and problems. Before I left the industry, the local dispatch had a couple of expensive multi-freq combiners into a couple of combiners.

An intermittent IMD problem arose, and we had a hell of a time resolving it, in fact, we ended up putting one station on a separate antenna, finally.

If there is ANY way around your problem, other than a combiner of some sort, I'd explore it.

RKG · Post by **RKG** » Tue Apr 10, 2007 7:07 pm

While I agree in general, with the Tx/Rx stuff, the system is pre-engineered by Tx/Rx for your precise frequencies. On the one hand, this means you can't add a channel or change a channel without re-engineering and re-canniing; on the other hand, we've not had any problems to date with this stuff (other than paying for it).

Bruce1807 · Post by **Bruce1807** » Tue Apr 10, 2007 8:08 pm

add a channel or change a channel without re-engineering and re-canniing

Not sure why not. The manuals all come with the tuning guide and its pretty simple.
I redid our 800Mhz 12 channel system with a split from 1/2 Meg to 1 Meg, no problem at all. If you have a network analyser available you can do it just as good as the factory.

RKG · Post by **RKG** » Wed Apr 11, 2007 5:59 am

The "T-Line" systems we have are specifically engineered for the specific frequencies we will be using. These studies do not cover any changes in frequency.

chpalmer · Post by **chpalmer** » Tue Apr 17, 2007 8:35 pm

We have a 4 channel system all within 300kHz of each other on UHF. TX/RX system works great but be ready for some loss... We pump in about 40Watts per transmitter and get about 5 at the antenna port.

Zaputil · Post by **Zaputil** » Tue Apr 17, 2007 10:33 pm

Combined antenna systems generally consist of 2 antennas, 1 for TX, 1 for RX.

TX combiners are picky about channel separation. Check specs. Frequency dependant. 150-300Khz between channels is common.

Expect about the same loss thru a combiner as you would get thru a duplexer.

It is good practice to use a window filter before the RX mulicoupler (mux). A RX mux may perform better than systems with a duplexer, since most have a preamp.

A good combiner/ RX mux system won't be cheap, but is worth considering depending on antenna space rent or limited space on the tower. Not very feasable to put up 20 antennas for a 20 ch trunked system.

Vendors will generally provide a design if you request a quote.

Another benifit is that the system will be balanced- all channels will have the same coverage performance. Again, important in trunked systems with muliple channels.

Good luck!

Bruce1807 · Post by **Bruce1807** » Wed Apr 18, 2007 3:24 am

The "T-Line" systems we have are specifically engineered for the specific frequencies we will be using. These studies do not cover any changes in frequency.

I think you mean T-Pass rather that T-Line.

We use the 800Meg T-Pass on all our sites and retuning is a piece of cake.
not sure why 400 can't be retuned as it looks basiclly the same only bigger cans. Do you not at least tweak the cans yearly?

http://www.txrx.com/product/product_vie ... 3B04185A2C

RKG · Post by **RKG** » Wed Apr 18, 2007 5:59 am

1. "T-Pass" correct; my glitch.

2. Don't know. There was a service contract provision in the contract, sub'ed to a well known local shop, but I'm not aware of the details. The system has been running for a tad over 2 years, and works beautifully.

Bruce1807 · Post by **Bruce1807** » Wed Apr 18, 2007 12:58 pm

In the quantar optimization sheet that is possibly internal use only but most shops would have a copy from commissioning it has power out from station and power out from combining.
We shut off all transmitters and check the o/p is within spec of the combiner as well as reflect from the combiner to the base
Any reflect can usually be made neglidgeble by adjusting the fine tune on the cans.
When we changed the split from 500k to 1 Meg we were able to reduce the insertion loss by adjusting the input loops on the cans.
greater the seperation the less insertion loss if tuned correctly.

bernie · Post by **bernie** » Fri Apr 20, 2007 5:48 pm

My two bits worth:
My thoughts on combining.
I have worked on, and re designed many radio sites over the years.

The typical site history is years ago some one put up a repeater with a couple of antennas on a hill top. Worked great, then along comes another, and another until nothing worked reliably.

Consider the cost of equipping each station with a full set of filters, IM panels, as well as the cost of coax and antennas. Tower space is expensive also.

Rf design of the site is dependant on the operating frequencies.
There are some things that should never be permitted:
Un shielded equipment, frequencies that have a harmonic relationship, inter modulation products, or RX-TX spacing below 500KC.

The closer the frequencies the higher the cost in both power and cost.
UHF, and 800 combiners get lossy when channels are closer than 250KC.
It is possible to combine close, even same channel with Ferrite hibred combiners.

If you expect all of the site users to operate as expected, you must have isolation between receive and transmit ports on all equipment, as well as TX-TX isolation for inter modulation prevention.
The isolation comes from physical separation of antennas, equipment shielding, filters.

Usually, a receiver multicoupler and transmitter combiner will accomplish
the goals at the most reasonable cost.

If you want to combine two repeaters on one antenna, the design of the combiner depends on the operating frequency spacing.

Case 1, Two UHF Ham repeaters with 50 KC spacing between operating channels.
Use a Ferrite Hibred 2 channel combiner with a 4 can Pass-reject duplexer.
Connect the receivers using a 2 way power splitter.
A low gain pre amp can be used. Pad amp output for 3 db site noise increase during effective sensitivity test.

Case 2, Two repeaters 10 meg channel separation.
Two 4 (or 6) can Pass Reject duplexers connected to the antenna with a phasing harness. The harness is made up of 1/2 multiple wave length cables.

In any case insertion losses, effective sensitivity and desensitization must be measured to assure that reality corresponds with theory.
In constructing home made combiners cable lengths can be "stretched" by using elbows. Fudge the lengths until the losses are minimized, and isolation maximized.

nmfire10 · Post by **nmfire10** » Sat Apr 21, 2007 6:03 am

We recently put in a big huge expensive $16,000 TX/RX work of art at our building. 6 UHF repeaters, combiner, RX Multi-coupler, and two antennas. Works great and someone else paid for it