Public Safety Repeater Duplexer?

[deathwinker]

MAKE SURE YOU'VE HAD SOME COFFEE FIRST BEFORE YOU READ THIS ONE!

I need some help figuring out how to build some duplexer cans for a portable, 50W repeater...and before you jump your guns, just wait, I'll explain.

I control radio comms for a Search and Rescue volunteer group, so we often find ourselves in remote areas well away from any conventional repeater systems. Our Mobile units only run 50W on a 33 foot collapsible antenna, so we don't get as much distance as we need to our teams on the ground with some 5W ht's. We have the ability to reprogram for different frequencies under Mutual Aid agreements, so we do have a rather vast expanse of area to use...geographical limits to our license is not an issue. I picked the ICOM CY-5000 as the repeater of choice for our command center, as it will be running 50W on 155.280. We are also in process of getting a 50 foot telescoping stick antenna as well. 50ft, 50 watts, 155.280. What we don't have yet is an input frequency, and I'm not sure what we would receive. HOWEVER, being that we have Mutual Aid agreements, it is possible that we can be granted access to a local fire station's or government's frequencies and use them ourselves. Again, the problem comes up, what kind of cans do I need, and how much work is involved in adjusting them for different freqs.

Any ideas guys?

 

[nd5y]

Antenna Systems Information from www.repeater-builder.com

 

[fineshot1]

MAKE SURE YOU'VE HAD SOME COFFEE FIRST BEFORE YOU READ THIS ONE!

I need some help figuring out how to build some duplexer cans for a portable, 50W repeater...and before you jump your guns, just wait, I'll explain.

I control radio comms for a Search and Rescue volunteer group, so we often find ourselves in remote areas well away from any conventional repeater systems. Our Mobile units only run 50W on a 33 foot collapsible antenna, so we don't get as much distance as we need to our teams on the ground with some 5W ht's. We have the ability to reprogram for different frequencies under Mutual Aid agreements, so we do have a rather vast expanse of area to use...geographical limits to our license is not an issue. I picked the ICOM CY-5000 as the repeater of choice for our command center, as it will be running 50W on 155.280. We are also in process of getting a 50 foot telescoping stick antenna as well. 50ft, 50 watts, 155.280. What we don't have yet is an input frequency, and I'm not sure what we would receive. HOWEVER, being that we have Mutual Aid agreements, it is possible that we can be granted access to a local fire station's or government's frequencies and use them ourselves. Again, the problem comes up, what kind of cans do I need, and how much work is involved in adjusting them for different freqs.

Any ideas guys?

IMO

In a public safety environment(and most others) there is no way your going to be able
to constantly retune duplexers back and forth between different freq pairs while in the
field. Duplexers are made to "set and forget" and constant retuning can be very
detrimental over time to a duplexer. Duplexers in most cases also require some pretty
sophisticated test equipment to properly tune them accurately and i imagine your not
going to have a radio tech with you on many field deployments. This is not very
practical.

Also in order to have the advantage that repeaters provide, you are most likely going
to need to deploy the repeater each time on high ground like a hilltop or a building
top, 50 foot mast or not. 50 feet for a repeater antenna on vhf-hi band is a waste
of effort without another height advantage. The coverage would be very limited to
a very small area without the height advantage. But if a small area is all you need
it could work, but then we are back to the above issue of the duplexer tuning.

Another option would be to use separate RX & TX antennas, however their in lies
another problem in getting enough physical separation between the rx & tx antennas
otherwise the repeater rx will experience desense from the power being radiated by
the tx.

I do not have any positive answers for you in your situation. Perhaps someone
else in a similar situation can chime in here and provide a solution or ideas.

 

[deathwinker]

Appreciate it.

That is kinda what I was fearing. I wasn't entirely confident that it could be done with a set of cans. The idea of two antennas, one set at 40ft and the other at 50ft, spaced about 50yds arpart was the only other suggestion that had been made. There had also been discussion about finding a bucket truck with a really long boom, and putting a mast up there, or just figuring out a way to keep a 100ft mast mobile. Either way, it sounds like a nightmare, but it's gonna get figured out eventually.

 

[prcguy]

I've assembled dozens of commercial repeaters and can tell you making a duplexer from scratch is completely beyond the skills of most people, not including the test equipment needed to align it.

If you can choose a transmit and receive pair that are more than 5MHz apart you can make use of inexpensive (used) VHF mobile duplexers.

These will tune as narrow as 5MHz and further separation is better. They will also work over maybe 100KHz so you can use them over a few close spaced channels.

Otherwise a real base station duplexer that will work down to a 1MHz split is somewhat pricey at around $250 on up used and a 6 cavity band pass, band reject version that will work down to a 400-600KHz split gets real expensive.

As another post mentioned these are impractical to retune in the field.
prcguy

 

[kayn1n32008]

Wirelessly posted (Mozilla/5.0 (BlackBerry; U; BlackBerry 9780; en-US) AppleWebKit/534.8+ (KHTML, like Gecko) Version/6.0.0.600 Mobile Safari/534.8+)

If you can get a pair that is 4.5MHz or more you should be able to use a mobile duplexer. Take a look at Sinclair Radio Labs, the have a decent website that will show you what their mobile duplexer need for min/max frequency seperation. Dual antennas for a portable repeater is not going to work too well. Also I would try and keep the power level to 15w to the antenna feedline, otherwise you WILL need a generator to keep it on the air.

The key to your portable repeater is going to be getting a second frequency that is minimum 4.5Mhz, preferably more, from your currently assigned frequency.

 

[ramal121]

Let me pick your first post apart. You have 50 watt mobiles at the command post with the ability to run antennas up 30 feet and it just doesn't make it to all the field portables (depending on the location).

By switching to a repeater at the command center, you will not gain much. Portable to portable will improve, but I don't think that is your priority. Those guys over the hill will still have a hard time getting back to the repeater, hence the command staff.

Making it portable and getting it to a high spot in roughly the center of the incident area is the only way to be sure to stay in contact with everyone.

Now the previous comments apply. With a wide freq spread, you could get away a lightweight mobile duplexer. If it goes below 3 MHz, your gonna need a monstrosity that is anything but portable. You will also not be able to be frequency agile. I agree with everyone, field tuning will get old quick and probably not great for the duplexer (if it can be done properly in the first place).

My suggestion is a small cross band repeater. VHF to UHF. Make it portable with a battery and solar panel. Assign a couple of monkeys to haul it all up to a hill and deploy it.

Now the command base can communicate, via UHF to this "remote base" and have great coverage on VHF. No duplexer, so you can set the VHF on any channel you want.

What would suffer is portable to portable coverage, sans the repeater, but is that a buzz-kill in your situation?

VIA TAPATALK