Re: [Repeater-Builder] Tuning duplexers with sweep generator?
w6nct wrote: I was recently told (by another ham) that I could ONLY tune up my 70cm duplexer cavities using something called a tracking generator. Unfortunately I do not have one; and judging the prices I have seem for things with that name on the web, I doubt that I can easily budget to purchase one. For some reason, I thought that my father used to tune up resonant cavities using a sweep generator, oscilloscope, and a frequency counter; but I don't recall the exact setup he used. I inherited his Wavetek (Model #1080, 1GHz) sweep generator, oscilloscope, and frequency counter. I also have access to an IFR-1100 service monitor, if I need it (i.e., can be borrowed from a friend). Can I tune up my 70cm duplexer cavities using the equipment I have? If so, could someone please indicate the test setup and procedure. Thank-you. Actually a network analyzer works better than a combination sweep and marker generator. Remember that when you change isolation, you are also changing impedance so you need to measure swr as well. There are other ways. Read Gary's excellent post carefully. -- Larry W1HJF rapp at lmr dot com
Re: [Repeater-Builder] Tuning duplexers with sweep generator?
I can remember using a bearcat scanner on a HP608? (hope that is the right model number) signal generator to tune pass and reject - used a 10 db / 50 Ohm attenuator between the duplexer and the test equipment to make for a better match. I have never used a network analyzer, but I have used several different service monitors with tracking generator. Steve NU5D
[Repeater-Builder] Tuning duplexers with sweep generator?
I was recently told (by another ham) that I could ONLY tune up my 70cm duplexer cavities using something called a tracking generator. Unfortunately I do not have one; and judging the prices I have seem for things with that name on the web, I doubt that I can easily budget to purchase one. For some reason, I thought that my father used to tune up resonant cavities using a sweep generator, oscilloscope, and a frequency counter; but I don't recall the exact setup he used. I inherited his Wavetek (Model #1080, 1GHz) sweep generator, oscilloscope, and frequency counter. I also have access to an IFR-1100 service monitor, if I need it (i.e., can be borrowed from a friend). Can I tune up my 70cm duplexer cavities using the equipment I have? If so, could someone please indicate the test setup and procedure. Thank-you.
RE: [Repeater-Builder] Tuning duplexers with sweep generator?
Your informant is essentially correct. A sweep generator is an instrument that generates an AF or RF signal either linearly or logarithmically between a start and an end frequency. By itself, it is useless for tuning cavities. However, when its sweep voltage is coupled to an oscilloscope's horizontal input, then we have a tool to visually characterize a cavity. A spectrum analyzer is essentially an oscilloscope with its input filter being driven by a sweep generator. A tracking generator is not really a separate piece of equipment, but is simply an output of the spectrum analyzer that can be used to excite the unit under test. The tracking in the name means that this signal generator is synchronized exactly with the sweep of the spectrum analyzer. Thus, the display on the analyzer is a graphic representation of the frequency response of the unit under test. A spectrum analyzer with a tracking generator, or better still, a vector network analyzer, are ideal for tuning duplexers, notch and bandpass filters, and ferrite isolators. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of w6nct Sent: Sunday, April 01, 2007 4:39 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Tuning duplexers with sweep generator? I was recently told (by another ham) that I could ONLY tune up my 70cm duplexer cavities using something called a tracking generator. Unfortunately I do not have one; and judging the prices I have seem for things with that name on the web, I doubt that I can easily budget to purchase one. For some reason, I thought that my father used to tune up resonant cavities using a sweep generator, oscilloscope, and a frequency counter; but I don't recall the exact setup he used. I inherited his Wavetek (Model #1080, 1GHz) sweep generator, oscilloscope, and frequency counter. I also have access to an IFR-1100 service monitor, if I need it (i.e., can be borrowed from a friend). Can I tune up my 70cm duplexer cavities using the equipment I have? If so, could someone please indicate the test setup and procedure. Thank-you.
RE: [Repeater-Builder] Tuning duplexers with sweep generator?
Duplexers and cavities have been tuned for many years without a tracking generator or spectrum analyzer. It is a little easier with a tracking generator or even a spectrum analyzer and a signal generator. But you can do the job with a signal generator that you can keep on frequency and a receiver. It helps to have some kind of signal level meter on the receiver but you can also just tune for quieting by riding the generator level so that the receiver is always noisy. That way you can hear if the level goes up or down. Using a sweep generator works fine for tuning pass band cavities or even the pass band part of a pass/notch type duplexer but you can't tune the notches with a sweep generator. The reason being is that the detector is not sensitive enough for the low signal levels that you need to work with. A typical diode detector will only work at about -20 to -30 dbm. Even if your sweep generator is able to put out +20 dbm that only lets you look down -40 to -50 db and the duplexer notch is going to be (hopefully) in excess of -70 db. You will never find the peak of the notch. So just a signal generator preferably a synthesized unit so you know what frequency it is on. You could use a tunable generator and a frequency counter but lots of generators tend to shift frequency slightly when you crank up the output level (high enough for the counter to see) and you will be working with the signal attenuated down to -80 to -100 dbm most of the time while tuning the duplexer. You can not afford to have the signal shift around or drift while you are trying to tune things as it doesn't take much of a frequency shift to mess up your tuning. With a good generator tune the pass bands at the proper frequencies first. Then tune the notches at the opposite frequencies. On the transmit cavities you would tune the pass to the transmit frequency and then tune their notches to the receive frequency etc. Then tune the pass tuning at the proper frequency again now that you have everything in the ball park. Then tune the notches again at the proper frequencies. ALWAYS tune the notches last. Do NOT touch the pass tuning again when you are done with the notch tuning. Tuning the pass just slightly will throw the notch way off. Be sure and have a dummy load on the port of the duplexer you are not working with and preferably 6 to 10 db pads on each of the ports that you are working with or you may not have the same tuning when you hook it up to your radio. 73 Gary K4FMX -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:Repeater- [EMAIL PROTECTED] On Behalf Of w6nct Sent: Sunday, April 01, 2007 7:39 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Tuning duplexers with sweep generator? I was recently told (by another ham) that I could ONLY tune up my 70cm duplexer cavities using something called a tracking generator. Unfortunately I do not have one; and judging the prices I have seem for things with that name on the web, I doubt that I can easily budget to purchase one. For some reason, I thought that my father used to tune up resonant cavities using a sweep generator, oscilloscope, and a frequency counter; but I don't recall the exact setup he used. I inherited his Wavetek (Model #1080, 1GHz) sweep generator, oscilloscope, and frequency counter. I also have access to an IFR-1100 service monitor, if I need it (i.e., can be borrowed from a friend). Can I tune up my 70cm duplexer cavities using the equipment I have? If so, could someone please indicate the test setup and procedure. Thank-you. Yahoo! Groups Links
