A tracking generator is nothing more than an RF signal generator with a swept output frequency. Said sweep is usually slaved to, and synchronized with, whatever spectrum analyzer is driving it.
Tracking generators are indeed used for, among other things, the tuning of bandpass filters. The idea is that you feed the signal from the generator into one side of the filter, then use the SpecAn to monitor the output. You then tune the filter for the smoothest 'hump' on the spectrum display.
I've done this plenty of times with older Motorola radios. Their VHF Syntor X series, for example, bottoms out at 150MHz. This won't work directly on the amateur 2-meter band, so the filter gets retuned, using the exact equipment you're seeing called out, so that its passband is changed to cover down to 144MHz on the low end.
If you don't have one, you're not going to be able to tune that filter accurately. You -might- be able to fake it with a generic sweep generator and a spectrum analyzer, but it'll be tricky because you need to EXACTLY match the sweep rate of the generator with that of the spectrum analyzer. If they're not matched, you'll never get an accurate tune.
If you can tell me which SpecAn you're working with, I may be able to suggest a matching generator.
Happy tweaking.
--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"
Could someone please straighten me out. What is a tracking generator? I know they go with spectrum analyzers, and I have always just assumed they were a controlled swept oscillator or something like that. What is their primary function? The reason I ask is I have to run through an adjustment procedure on a spec an, and I need to tune a bandpass filter, and it calls out for a tracking generator. We unfortunantely don't have one, so I'm trying to find out what they actually do and can't find much on google. Is something that a sig generator in sweep mode could accomplish (i.e. an 8660...) I'm sorry for the vagueness of my question, and will give more info if necessary.
Thanks for your time, and as always, all replies greatly appreciated. Steve
that is a programmable signal sweep source needed to inject into your filter so that the monitor can view the status of the filter. service monitors (most any ways) have this option in places where you may need to align duplexers and such etc... my service monitor is getting old now even though it's in mint shape (IFR type). it only covers up to 1 Ghz in sweep. maybe i will sell it for a newer unit! who knows.
--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
Actually, that's what I've been doing so far. Since we don't have a tracking generator, I've just been using our specan, (hp 8568a) with our 8660b in fast auto sweep mode, and it just so happens to sync up with the spec an w/ a sweep time of 100mS (very tricky indeed), and I can only use this for ballpark adjustments. To tune it in I have to put it in single slow sweep mode, and put the specan in max hold and wait for the sweep to finish (takes forever each cycle). Now, however, our spec an failed its performance test, specifically the resolution bw switching uncertainty test.
The table is: all measurements in dB, tol at 3Mhz and 10Hz +-1dB, all else +-.5dB
3Mhz .07 in
300kHz -.28 in
100kHz -.92 out
30kHz .69 out
10kHz .41 in
3kHz .32 in
1kHz 1.84 out
300Hz -.13 in
100Hz -.37 in
30Hz -1.08 out
10Hz -7.70 way out
This is where I stopped the performance tests, I know I should go through them all before I go adjusting, but it is a loooong procedure, and if I just have to redo it all again.... Hoping that it is just adjustment, not repair needed,... P/ the S.M., the related adjustments for this procedure are
The 3MHz filter adjustments call out for the tracking generator. To set up the equipment, verbatim from the manual:
Disconnect 97 (white/violet) cable from A4A8J1 and connect tradcking generator to A4A8J1 using BNC to SMB snap-on cable.
Set spectrum analyzer SCAN WIDTH PER DIVISION to 20kHz and red scan width knob to ZERO. Set TUNING STABILIZER switch to ON. Set tracking generator output level to -25dBm and tune spectrum analyzer FREQUENCY for a tracking generator output frequency of 21.4000MHZ.
There is only a single cable from the tracking generator going into a4a8j1, and there aren't any sync lines between the specan/tracking generator and the 8568a.
**So is this just a center frequency of 21.4MHz w/ a sweep width of
200kHz, or is it CW at 21.4MHz? The procedure starts with filter peak adjust, and to connect scope chA to tp7, chB to tp5, adjust tracking generator output frequency to peak ch a display, then adjust a cap for maximum peak to peak level on chB. This is then repeated at different test points, and adjusting different caps,.. and finally using the spec an crt to achieve final peak. Then for center and symmetry. Still nothing about syncing the tracking generator to the 8568a. It says to bypass, one by one, the xtal filters and adjust for minimum peaks and symmetry. This all makes sense, but there isn't any adjusment of sweep time, or syncing the two spec an's, or anything like that.
The other tests only require DVM, step attenuator, power meter, etc..
So, what would you make of this? Is the tracking generator inputting a swept frequency to the 8568, or is it CW? Think it's possible to use the 8660b for this?
HP 8568a.
Also, the manual calls out for an HP 141T/8552B/8553B/8443A.
If I need to clairify further, please let me know. Sorry if this is confusing, and thanks for the quick response. Thanks, Steve
Gotcha. You're in luck. I believe the HP 8444A-OPT 059 tracking generator is compatible with that analyzer. What happens is that the SpecAn outputs a swept IF freq that is in sync with its sweep rate. Said swept output is plugged into the tracking generator, and the output of said generator then goes to the filter. Vyola! Perfect match.
You shouldn't have much trouble finding the 8444A (they turn up on Greed-bay periodically), but be absolutely POSITIVE it's the OPT 059 model. This option adds a self-contained third local oscillator to the tracking gen, and makes it truly usable with many anlayzers it might not otherwise be able to work with.
Happy hunting.
--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
(Known to some as Bruce Lane, ARS KC7GR,
kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
"If Salvador Dali had owned a computer, would it have been equipped
with surreal ports?"
I'm confused. If you have a spectrum analyzer, couldn't you just use broadband noise as the filter input and look at the resulting spectrum to see the characteristics of the filter?
I'm confused too. For our purpose, we need signals in the range of
0-10dBm. We use the swept signal generator to tune in transponder taps. You have to use an antenna to transmit into the tap, and the tap attenuates the signal by 25dB, so after antenna loss and the attenuator loss, the signal is significantly less. Having a tracking generator for this would be much more agreeable than using the ballpark method.
Not sure about using the broadband noise for tuning the filter...
Oh, you should ignore me, I wasn't responding to your original query, just just hoping someone could explain why the tracking generator was necessary when the output was being interpreted by a spectrum analyzer (vs a scope).
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