Batboard

I have a 110 watt TTE 1452A (with a single-stage circulator) that seems to peak at 441 MHz +/- 3 MHz
I need it to be on 448 MHz where now the power is way way down.
The circulator says it is not tunable.

The amplifier modules have tuning pads connected by jumpers. i assume by adding (back), or removing jumpers, I can shift the frequency to 448 where I want it to be. Does anyone have a procedure for this?

Do you know if the amps tune in the obvious way? i.e., less capacitance = higher frequency?
Or, through the magic of maching networks, does it work in the opposite way?

Thanks
Ken
KE2N

There should be no tunning involved with the amp. It all depends on what your drive power is set at. Your mileage will vary a bit but with 7 or 8 watts of drive should obtain the output you desire. Are you using this as a stand alone amp or are you running it in a MSF repeater configuration?
Doug

I will be using it standalone (but with the built in circulator if possible).
The repsonse is very peaked and falls off on both sides of 441 - here is the high side response
441 MHz 120 watts out
442 117 watts
443 113 watts
444 105 watts
445 90 watts
446 65 watts
I did not try higher than this but
I need to operate it on 448 MHz

Ken

The trimming capacitors are factory-set, possibly to differentiate the 403-435 vs 435-475 MHz ranges. The entire PA is wide-band and should cover 435-475 MHz equally well, within a couple of dB. There is nothing to tune in the PA. The IPA output controls the overall power of the station, but even so, the output power shouldn't really "peak" anywhere special. Typical PA drive is 3-5 watts. The IPA output power is controlled by sensing the PA output power and the temperature of the PA heat sink, the temperature of the dummy load in the circulator, and the ambient temperature. When things get too hot (probably way above 150F), the power will be reduced.

Bob M.

OK - that all sounds nice ...
but looking at it, I can see that someone has (previously) been soldering on the tuning pads provided and the frequency response is in fact very band-limited.

Using more-or-less constant drive power (roughly 5 watts) I see this:

441 MHz 120 watts out (27 amps at 12.0 volts in)
442 117 watts
443 113 watts
444 105 watts
445 90 watts
446 65 watts

(I need to go to 448!)

it has a similar drop-off as you go below 441,

Tonight I think I will disconnect the isolator and measure its frequency response.
It should have -3 dB points that are below and way above this range, from what people are saying.
But I think I should rule that out first.

Then I suppose the next step is to look at the response of each cascaded stage starting with the low power one.
I am expecting to see approximately 5 dB gain from each stage....
I will report back what I find.

Ken
KE2N

the single stage isolator seems to be designed for 470 MHz - there, it has a distinct peak of 30 dB return loss and about 1 dB insertion loss.

Return loss stays in the 20 dB range though the 440-460 MHz range, though, and that should be sufficient to protect the finals.

Insertion loss starts to creep up a little below 460. But if you are talking 3 dB points, the bandwidth is huge (like 400 - 500 MHz or wider).

So - the conclusion is: the isolator is fine and I need to look at the individual amplifier stages.

Ken

OK - so I finally arranged an exciter with a continuous power adjustment and this is what I found:

Input/output
1.5 5
2.0 50
2.4 90
2.5 100
2.6 110

And, with small tweaks to the drive, it puts out 100+ watts from 434 to 449.9 MHz. Very nice.

I imagine that the other radio I was using as a driver was varying *its* output with frequency and that was making a huge difference at the output of the big amp.

Ken

It sounds as if you're using that unit as a stand-alone PA and NOT as part of a complete MSF5000 station.

As Jamie of Mythbusters would say, "Well, there's your problem!"

Bob M.

That is correct.
The TTE part number (subject/title of this topic) is the part number of the amplifier, not the repeater.
But that was not the problem.
The problem was me not measuring the drive power accurately at the start, combined with a lack of appreciation of just *how* non-linear a class C amplifer like this actually is...