[Elecraft] Potential Elecraft Kit

[G3VVT at aol.com]

In a message dated 13/04/05 01:44:15 GMT Daylight Time,  
wlreed11 at earthlink.net 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?



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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