Wireless Connection of 2 repeater stations

[KMB]

Hello,

Our company want to connect our individual repeater stations, when our outdoor staff use their portable radio to uplink to the repeater in Zone A then the downlink will reach the repeater in Zone B so that the outdoor staff here can also hear and communicate with each other. It is because both zone is quite far away that portable radio cannot reach the repeater in each zone directly.
Our technical support contractor sugguest using "frequency linkage" instead of fixed line. There will be a mobile radio in each zone, to receive the downlink from opposite repeater and transmit the signal to the repeater to re-transmit,e.g. Mobile B will receive the downlink from Repeater A and transmit to Repeater B to re-transmit out. Our setting is using Spectrum MXD800 repeater and GM300 mobile radio with RVS-8 router for selection of incoming signal in each station.

My question is, is it possible and difficult to do that?

Thank you!

KMB

[wavetar]

I'm not familiar with the Spectrum repeater, but I have done what you are asking with GR1225 repeaters linking with CDM radios. It was not overly difficult. As long as the Spectrum has readily available connections for ground, PTT, TX IN, RX out and COR, you're in business.

Todd

[psapengineer]

Yes, it is possible, but, some things to watch out for include:

Necessary cavities, isolators, and duplexers for filtering and combining.

Intermodulation products

Do plan on using different CTCSS tones for the control links

Set up time, it takes a long time to get the entire system up and on the air following the first push to talk from a portable. Something on the order of 4 or 5 syllables may be lost if you don't wait to talk.

You'd be better off to install a full duplex 900MHz control link that is always on the air between the two sites; this will really help with the set up time. Of course, its lots more expensive......

You may need a voter or audio mixer to select or combine the audio............

Good Luck.......... Bob

[KMB]

Thanks wavetar and psapengineer!
I forget to say that our working frequency is VHF (166~170MHz).
Would youu give me some suggestions or details on the configuration to set up a wireless linkage? I want to get some ideas before I go with my contractor.
Our problem now is when the contractor do the trial, when both repeater try to communciate each other thought voter-connected for signal selection, there is continues "keying" or say "jam" to the repeater stations. However, there is no problem when the mobile radio directly connect to repeater. What's wrong?

[aaknitt]

This is just a guess, but it sounds like you've put a receiver at site "B" to listen to the output of repeater "A" and key up repeater "B". However, when repeater "B" keys up it is desensitizing the receiver (at the same site) that is listening for repeater "A", which makes the repeater drop. The same thing is happening on the other end of the link, which causes the repeaters to "ping pong" back and forth keying each other up continuously. The root cause of this problem is inadequate isolation between the new receiver and the repeater transmitter.

Another possiblity is that you have the two repeaters with opposite receive and transmit frequencies. This would also cause a continuous "ping pong" lockup.

If all you want to do is link two VHF repeaters together, the best solution is probably a simple single-frequency link on another band, like UHF. A UHF radio at each repeater site would do the trick, and you don't have to deal with the isolation issues that you would when doing the linking on VHF.

Again, these are guesses because I'm not exactly sure what your setup is.

Andy

[KMB]

Thanks aaknitt!
Yes, your guess is right! The contractor and I also think about that!
So, anyone can help me to give me the ideal configurations for the set up we want? So that we know the idea from my contractor is acceptable.
Any information can be found from internet??

And, what type or model of isolator suggested?



Thanks and 73 de
KMB

[psapengineer]

You might look at:

http://www.simulcastsolutions.com

They provide equipment to do wide area coverage solutions. If the two transmitters/repeaters don't have any area of interest where both can be heard you don't need to frequency stabalize and audio syncoronize them.

Look under their case studies, white papers, and presentations for more information.

Essentially both repeaters should be programmed both the same/idential PL and Freuqncies and then the linking and voting between the two must do the control and audio selection. If the repeaters offer keying priority, the "remote control/wireline" input should be prioritiezed higher than the "in cabinet" local repeat. This will get the repeaters on the air sooner and help with dropped syllables at the beginning of a transmission as well as provide some sort of backup in case of control link failure.

Also, remember to program "talk around" in the portables...............

Good Luck...........

[aaknitt]

If I understand the situation correctly, he's not trying to do a true simulcast or voting system. He's simply trying to link two distant repeaters (each on a different TX/RX pair) together.

As I mentioned before, I think the best way to do this is with a UHF link. This would require a UHF radio and antenna on each end that are interfaced to the repeater controller. This eliminates the continuous "ping pong" that results from trying to use the output of the other repeater for the link. Repeater hang times cause the "ping pong" effect. The UHF radio at site "A" is only keyed when an input to that repeater is present. The UHF radio at site "B" hears the UHF signal and keys the distant repeater. When the user at site "A" unkeys, the repeater at Site "A" drops, and the UHF transmitter drops, which means the repeater at Site "B" also drops.

The difference in using an additional link frequency is that the local link transmitter only transmits when the user is accessing the local repeater. The repeater output frequency, on the other hand, transmits regardless of whether the user is accessing the local or distant repeater, which is why using the other repeater's output frequency for linking results in continuous "ping pong". Kind of hard to explain without drawing lots of pictures, but if you think it through enough times it should become clear.

Andy

[KMB]

Thanks for both information.

It is diffiuclt to us to use UHF for linkage because our local authority only give us 4 pair VHF repeater channels.
Our repeaters are located on the top of the water tank of building (around 40 floor high, around 120 meter) which area is just around 15m x 15m, it seems difficult to isolate the receiver antenna, what is your suggestion to make a isolator to it?

Thank you!!

KMB

[aaknitt]

You may have already figured out a solution to your problem right now, but if not, there has been a good discussion going on regarding this topic (in-band linking of repeaters) on the Repeater-Builder Yahoo group. You'll need to have a yahoo account and join the group to see the postings, but if you do that, search for the topic "Linking two shared repeaters". There are a lot of good posts describing systems just like what you're trying to do.

Andy