EMRFD Message Archive 3965
Message Date From Subject 3965 2010-01-11 17:22:36 elia_2e0zhn Spectrum Analyzer Assistance Please Hi Everyone,
I hope someone can help me with some information/suggestions on the following spectrum analyzer: http://www.tti-test.com/products-tti/pdf-brochure/prec-tsa-2p.pdf
What I am planning to do is add a tracking generator but have no idea what the 1st IF of this analyzer is, can anyone help or suggest a way to find this out please?
I know this is not directly related to EMRFD for which I do apologize but I know that there is a wealth of experience in this group and thought someone can help out.
Thanks in advance,
3966 2010-01-12 00:03:17 drmail377 Re: Spectrum Analyzer Assistance Please Hello Elia,
For others in the group, the "spectrum analyzer" Elia refers to is a 250MHz or 1GHz spectrum analyzer "adapter" for a standard oscilloscope manufactured by Thurlby Thandar Instruments.
The simplest way to control a tracking generator with this adapter is to tap-off the sweep output from the spectrum analyzer adapter to the horizontal input of the oscilloscope and feed it to a sweep generator. Your generator is then essentially a voltage controlled oscillator. No need to know anything about the IF of the spectrum analyzer adapter. Plus now you can set the oscillator to sweep any frequency range independent of the analyzer adapter, this allows you to test two-port devices like a mixer or up/down converter. From the adapter data sheet the sweep voltage is 0.5V/division. So for 10 divisions I expect the output is a sawtooth wave that goes from zero to five volts. Just sweep the generator with this signal - hopefully it isn't sweeping too fast for the generator.
Keep in-mind just sweeping a generator with this adapter doesn't really give you a scalar network analyzer. Depending on your needs, you should consider at least some sort of leveling control for the generator. Plus, unless you have a digital oscilloscope that can save and subtract waveforms, you have no way to calibrate and normalize the trace. Even if your digital storage oscilloscope can store and add/subtract waveforms, you would have to figure out a way to interrupt the oscilloscope sweep and then manually allow it to sweep again so you can calibrate/normalize than insert the device under test.
If you already own this spectrum analyzer adapter, then try what I suggest in the paragraph above. If not, then before you buy that spectrum analyzer adapter, I suggest you take a look at the Vector Network Analyzer (VNA) calle VNWA-USB by DG8SAQ that uses a PC at this link:
This VNA connects to the PC via USB and covers 1kHz to 1.3GHz+ It has a spectrum analyzer function too. It is available as a kit, but ready-built units have recently become available. A commercial VNA for this frequency range will cost you from around $3,000-$5,000 (used on ebaY, good luck) through $50-100,000 (new). The kit form of the VNWA-USB will cost you roughly $350 USD.
There is a very active Yahoo Group for the VNWA mentioned above. Join the group for more information
3970 2010-01-12 06:49:40 elia_2e0zhn Re: Spectrum Analyzer Assistance Please Hello David,
Thanks for your informative reply.
Yes I do have this adapter already, I got it from a fellow ham at a very good price (half of the price of the VNA you mention)
I got a response on the 1st IF and VCO frequencies so now I have two methods of adding a tracking generator. The main use I have for the adapter right now is to check the response of some homebrew filters so a scalar netwrok analyzer not needed right now... (but that is to be my next toy :))
Once again, thanks for your reply. My target now will be to integrate the tracking generator into the adapter case if possible, if not then your method will be tried next.
73's Elia, 2E0ZHN
3971 2010-01-12 08:36:51 Hugo W. Catta Re: Spectrum Analyzer Assistance Please 3972 2010-01-12 09:07:03 drmail377 Re: Spectrum Analyzer Assistance Please OK Elia. Some ideas: Mix the spectrum analyzer VCO and LO's up again, voila, tracking generator. Forget all that, build a simple noise generator to stimulate your filter and see the filter response on the spectrum analyzer (refer to EMRFD). Generate noise from your PC's sound card using a PC sound-card generator application, up-convert it to your filter frequency via a mixer then see the filter response on the spectrum analyzer adapter. Hmmm...
Caveat (stating the obvious): What's said in this post sounds simple - but the devil is in the details: buffering/impedance match, signal leveling (all levels in-general), images, etc. etc. Resistive pads are your friend. Avoid active gain blocks wherever possible (may be difficult with the sound-card approach).
As you haven't told us about your application and background... I'll be motherly here: Pads and noise generators are covered in EMRFD. Read-up. Pads and known-good shorts, opens, and loads are your friend.
Again, I strongly suggest you get a PC-based VNA. The VNWA is the way to go. I have an early version of the IW3HEV VNA (back then it cost a lot less), proven performer but out of the box doesn't have the capabilities of the VNWA and now costs more. miniVNA info:
http://www.w4wb.com/Misc/miniVNA.htm <= USA
http://www.wimo.com/instrumentation_e.html <= EU
3976 2010-01-13 15:50:49 elia_2e0zhn Re: Spectrum Analyzer Assistance Please Hi David,
Once again thanks for your valuable input.
What I am trying to do is tune some homebrew filters (BPF, LP and crystal ladder filters) that will go into my transceiver.
I think I have enough information now to start working on the tracking generator (or use a noise source).
Thanks again to you and all others that offered help offline.