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Harmonic filter tuning after Circulator

This forum exists for the purposes for discussing service monitors (This includes but is not limited to Motorola, HP, Aeroflex, GD, etc). Additional topics allowed include test procedures, interpretation of test results, where to find information about specific tests, antenna VSWR, return loss testing, duplexer and filter alignment, etc.

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fineshot1
Posts: 910
Joined: Wed Oct 12, 2005 5:13 am

Harmonic filter tuning after Circulator

Postby fineshot1 » Wed Dec 14, 2016 7:02 am

I tuned a single stage circulator and wondering which harmonic (2nd, 3rd, 4th or 5th) to tune the harmonic filter for.
This is for my ham repeater in the 222 ham band. Which parameters most determine exactly what frequency to tune
this filter for?
fineshot1
NJ USA

Al
Posts: 1045
Joined: Tue Sep 04, 2001 4:00 pm

Re: Harmonic filter tuning after Circulator

Postby Al » Wed Dec 14, 2016 6:49 pm

Unless you have a special filter, usually they're just a lowpass filter with only one tuning adjustment and not a real sharp rolloff. I would tune it so that the loss starts to increase at 40-50% above your 222 Mhz frequency. Then you should have minimal loss at 222 Mhz.

fineshot1
Posts: 910
Joined: Wed Oct 12, 2005 5:13 am

Re: Harmonic filter tuning after Circulator

Postby fineshot1 » Thu Dec 15, 2016 5:28 am

Thanks Al,
EMR model no 6451/F but i can not find any exact model no doc on it but i did find one that is
close to it physically and model no wise to it and it seems it may be a 2nd harmonic filter. See
very similar one below.

http://www.emrcorp.com/doc/uploads/d43a ... _02.14.pdf
fineshot1
NJ USA

Al
Posts: 1045
Joined: Tue Sep 04, 2001 4:00 pm

Re: Harmonic filter tuning after Circulator

Postby Al » Fri Dec 16, 2016 2:59 am

I couldn't find the model number that you listed in my 2011 EMR catalog. Does your unit have one or two piston capacitors with caps for adjustment? One way to verify if you have a service monitor or a sweeper+spectrum analyzer is run a quick sweep to observe the passband chacteristics. If you do indeed have a harmonic filter you'll see a notch in the passband which will be frequency-adjustable with the one capacitor. In that case, I'd set it to reject the second harmonic of your 222 Mhz frequency. If you have two caps on the unit, it might be a line matcher model 6450(I use them here)series.

fineshot1
Posts: 910
Joined: Wed Oct 12, 2005 5:13 am

Re: Harmonic filter tuning after Circulator

Postby fineshot1 » Fri Dec 16, 2016 5:31 am

Al wrote:I couldn't find the model number that you listed in my 2011 EMR catalog. Does your unit have one or two piston capacitors with caps for adjustment? One way to verify if you have a service monitor or a sweeper+spectrum analyzer is run a quick sweep to observe the passband chacteristics. If you do indeed have a harmonic filter you'll see a notch in the passband which will be frequency-adjustable with the one capacitor. In that case, I'd set it to reject the second harmonic of your 222 Mhz frequency. If you have two caps on the unit, it might be a line matcher model 6450(I use them here)series.


Yes Al - one capacitor to tune(that's why i referenced the 6450) and yes there is a notch in the passband. Thanks
fineshot1
NJ USA

com501
Posts: 1000
Joined: Fri Nov 02, 2001 4:00 pm
What radios do you own?: Over 50 - All Motorola

Re: Harmonic filter tuning after Circulator

Postby com501 » Wed Dec 21, 2016 5:23 pm

All post circulator filters are tuned to twice the transmit freguency to suppress the even harmonics of the isolator.

fineshot1
Posts: 910
Joined: Wed Oct 12, 2005 5:13 am

Re: Harmonic filter tuning after Circulator

Postby fineshot1 » Sat Dec 31, 2016 8:39 am

ok - happy new year folks and thanks for the help

the notch in the passband is now properly tuned for the correct frequency. Thanks
fineshot1
NJ USA


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