Using an isolator outside of rated band...

[thehead7]

Hello,

I have this cellular amplifier that I picked up to use as a repeater amp.

My question is this: The amp has an internal isolator that is rated for something like 850 or so through about 904. I think it's made by alcatel? Anyhow, what, if any, would be the adverse effect of trying to run 936 mhz through it? It would seem to me that it would increase the swr on the input port of the isolator, but I don't know if it would be enough to make a difference.

I will also be running an isolator that is part of the duplexer that I am purchasing (a nice rack mount TxRx Combline unit). Should I just pull out the isolator and rely on the external isolator? I kind of like the idea of having an isolator inside the amp.

Any comments would be appreciated.

73
John

[Jim202]

Many isolators have a manual adjustment on them. You can try and look to see if yours has this adjustment. You could also try contacting Alcatel and see if they will talk to you about the isolator. Try and see if it will go up to the frequency you want to run it at. If they do talk to you, ask how to adjust the unit you have, if it can be adjusted.

Jim

[bernie]

My two bits worth:
Isolators (circulators) are usuially rather wide.
It is a transformer that is magnetically biased. Because of this maginet never mount it on a steel surface unless the specs permit it.
It also must be followed by a harmonic filter.
The energy introduced into the in port rotates because of the magnetic field to the next port that has the correct impedance. The winding of a circulator resembles a Mercedes star sandwitched between two ferrite pucks with a powerful magnet at 90 deg angle to the core.
The ports are very impedance sensative, that is why there are adjustments.
In general here is how you tune one:
If it is of the tuneable variety there will be 3 tuning adjustments, one by each port.
Adjust the input and output ports for least loss. You could use a tracking generator, tuneable receiver, and signal generator.
Reverse the input and output ports, set the load capacitor for least signal.
If you remove the load the loss will go to a few DB.

If this is a 5 port device align the input, output, and two adjustments in the center of the can for least loss.
Reverse connections, remove one load, align the other for minimum signal, Replace load, remove the other, set the remaining load tuning for minimum, install other load.
It is possible to fine tune the input port for least refelected, which should be rather low if aligned as above.
In operation it should not run very warm unless it is on a heavy duity application such as Pageing, or trunking control.
Hot loads usuially indicate the cavity has gone out of tune.

[thehead7]

Thanks, Bernie and Jim, for the input. The isolator module does not seem to be adjustable. The amp itself is not very big. It is almost all heat sink, which is a good thing. Inside, there are just two ceramic PCBs, and one regular PCB with control circuitry on it, and this isolator module. I am in the process of trying to find the correct connectors so that I can sweep it and see how it looks. If it doesn't look promising, I fully intend to chuck the thing over my shoulder and stick with my external isolator, which should be quite sufficient for my needs... I will have to do some screwing around with this thing no matter what, I suppose, since it's made for a completely different application. I'm about to take a long, hard look at this thing for a while and see what I can figure out.

Thanks again for the input, and I'll file bernie's explaination of tuning procedure for the circulator away for future reference, as I'll probably need it sometime.

THanks,
John