Home-Brew Spectrum Analyzer

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f you've always.m. 0 I

pectrumAnalyzerProject for DXers and experimenters alike.

byGregory R. Mclntire KE0UV

. .. but figured itw v o u t of vour budeet. here's- - . - ~ .answer All the components re-

may be found in abox In the worsti t l l run you less than ten dol-

as long asyou already own anSW)

Theory and ConstructionSince it's unlikely many ofyou have the same scope and SW

receiver I use, I give relativelygeneralized instructions here. Witha little care, however, you shouldbe able to easily apply this ideato most models of SW receivers,and to almost any oscilloscope. Ifyou have my particular setup,though. contact me for help onfinding the specific connectionson the DX 360. Please send an

receiver scans across a re- of your HF transccrver. Using the latter sys- of the board, it was tough figuring out whata DC voltage proponronate to tern. an s~gnalon the frequency to which was what. After a lot of trial and error, 1strength of the received slgnal causes the your transcerver 1s tuned will show up in the found what I was looking for. It's easiest if

on the scope's CRT to deflea upward. enter of the CRT.This srgnal. too, marks one terminal of the tuning capacitor is con-soon s the scanner passes by the signal. the middlc of the spectrum range the analyzer nected directly to ground.

Thls system IS surpns~ngly lm-lmaprne a "scannrng recerv-whose IF output IS rectrfied

ck down. if the scan rate, a continuous trace appears onCRT with vertical spikes or deflecrrons of

thern the path of the scanner.h ~spectrum analyzer ~nrerfacewntalns

own HF receiver. Simply tune the SWspectrum

SASE.Rrst. obtain almost any simple,low-cost scope. I use a fortydol-

is lo ok ~n ~rThe amount of spectrum you can view de-pends on the amount of bandwidth availableat the IF (beforethe final IF filtering) of yourtranscerver Thrs also q u i r e s that the IFfrequency bc wrtlun the tunlng range of theSW rurerver. If your IF is455 kHz you canuse a simple AM broadcastband receiver.

DC T h ~sC lpnal IS then fed lar, 2 MHz sed scope.Photo A Top vteu? f the spennun a m l n e r ~nrerface. Next. obta~n s~mple, C tuned.The scope's trace beam shortwave receiver. My Radiothe face of the CRT at exactly the same you want to v~ew. rfeed the antenna Input of Shack Reallsuc DX 360 works great. How-Thus. the S W re eiver wlth the wldeband IF srgnal ever, slnce I couldn't s he component side

Now see the schematic in Figure 1. Thereceiver provides the signal@C voltage) forthe oscilloscope to display. All you have tobuild is a very simple device that will 1)cause the receiver to scan a portion of theHF spectrumand 2) rovide a"sync" slgnalto the scopes it will also scan heCRT t thesame rate.

Figure I Schemat~cor the 10or Less hom e brew speo nun analyzer. Figu re 2 . Foil side of bwrd n nl ize.73Amateur Radfo February 1990 41


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Home-Brew Spectrum Analyzer

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