In a message dated 13/04/05 01:44:15 GMT Daylight Time, [EMAIL PROTECTED] writes:
One of the insturments I always wanted for home use was a spectrum analyzer. Nice to have sound card analyzers with software and all, but a real rf analyzer in a small, functional package would be sooooo great. With some careful trade off decisions it might even be affordable! The display is a big headache if you don't have a good Oscope handy but a creative designer [or two] might be able to do the job. I suppose it would not have the broad appeal of a K1, 2 or even a very compact antenna tuner, but it might appeal to a few hundred hams and others who do bench work. Wayne K9NE Yes, I know about the projects already on the web, but how many of you have actually rounded up all the stuff to build that one? -------------------------------------------------- Al Helfrick, K2BLA did a series of articles in the 1980's on just such an idea. The one published in "RF Design", January 1988 had a 3 chip design for use with a cheap general purpose oscilloscope and was based on the MC3356 chip as the heart of the project. In November 1989, "Radcom" published an article by Roger, G4PMK that expanded on Al's ideas with a practical version that would cover 1 - 90MHz with a logarithmic display, 50dB dynamic range and a built in marker generator. The MC3356 converts the incoming 1 - 90MHz up to 145Mz where a Toko helical filter provides some selectivity. Is then down converted to 10.7 IF with an NE602, at which point the main selectivity is achieved with filters. The clever bit after this is the use of the second section of the MC3356 chip to provide a logarithmic IF and detector. A kits of parts and a PCBs were offered at the time so one was built. My basic analyser covers up to 97 MHz and have extended the range with external converters up to the 70cm UHF band. Believe the MC3356 chip is now obsolete so could be difficult to replicate. A handy tool for tracking down RF spurii and interference problems within it's capability. Commercial small spectrum analysers tend still to command a premium price on the surplus market and the main that are available tend to be large and heavy. I have such a one, the HP 141T/8554B combination. Can make your eyes bulge carrying the instrument, but still has a good performance considering it's age. This was our instrument of choice up to recent years with the HP 8555A plug in for maintaining analog microwave systems. For my own personal use at home tend to use the homebuilt device first and only pull out the HP 141T when circumstances force me to. Noticed a more recent design offered at a hamfest last year that covered up to 500MHz or more with what appeared to be a cable TV tuner at the front end. There are probably other built and kit versions of these spectrum analyser adapters available in the market. Bob, G3VVT _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
