At 11/21/2004 11:01 AM, you wrote:
>Joe,
>
>I suspect that RJ Communications is no longer in business, so finding
>tech data on that circulator may be difficult.
I know someone who has one of these & sold many more (if we're talking the
same model; is it rather large for a VHF circulator?). IIRC the
performance on 2 meters was excellent: 0.3 dB forward loss & ~30 dB reverse.
>The typical ferrite circulator doesn't dissipate much power itself; it's
>the load(s) attached to the reject port that determines its power
>rating.
If you expect it to handle 100% reflected power, yes. Circulators do have
their own power ratings - you can't slap a 1 KW load on one & expect it to
handle that much power. The lesser of the two (circulator & load)
determines the power it can handle under any conditions, but in a pinch you
can put as much power in as the circulator can handle so long as the power
reflected back does not exceed the rating of the load. Of course if your
antenna unexpectedly goes bad you'll fry the circulator load.
>It's important that a circulator be correctly tuned to operate
>efficiently. The label 140-180 MHz refers to the range of that
>particular design, and should not be taken to mean that it will work at
>any frequency in that range.
Again, if we're talking about the same circulator, it's rather broad. It
worked just fine all across the 2 meter band & then some, with no tuning.
> Nearly all of the circulators I have taken
>out of service from the 152 MHz band would not tune more than 2 MHz
>either side of the frequency marked on the unit. I had to send them
>back to the manufacturer to be reworked for operation on the 2m band.
>This rework involved an exchange of magnets, pole pieces, and a new
>garnet ground to a specific tolerance.
>
>A network analyzer is a must for tuning a circulator, especially a dual
>circulator, since some measurements look for transmission peaks while
>others look for return-loss peaks. A spectrum analyzer will not suffice
>for this tuning task, unless it is used with a return-loss bridge.
This is not true. I've tuned all my circulators using only transmission
measurements (forward & reverse).
Bob NO6B
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