The Heathkit SB-620 “Scanalyzer” is an IF spectrum analyzer. It graphs the amplitude of signals around the one that your receiver is looking at, so you can see all of the signals around you at a glance. Problem is, it has to be setup for the particular IF frequency of your receiver. The original kit included parts for a wide range of IF frequencies. Only one frequency could be installed though and my unit had the wrong frequency for the classic Heathkit SB-301 receiver I have.

The pdf article describes how to convert it to the IF frequency common to many Heathkit receivers, including: SB-100, SB-101, SB-110, SB-102, SB-104, SB-300, SB-301, SB-303, HW-100, HW-101 and HW-104. The photo above shows it operating with actual 80m signals. Get the article and schematic below:

Reader Comments

Posted by Steve L.

November 01, 2013 - 08:47 am

Hi Dale, I'd like to help but don't have enough info on your problem. Did you follow the steps in the "Adjusting the Scanalyzer" section of the article? How did that go? What exactly are you seeing on the Scanalyzer screen? I take it that there is a horizontal line. Is there just one pip in the center? Be aware that it can be tough to get the controls on the SB-620 set properly to give a good display. Set wrongly, it might very well look like it isn't working. PIP Gain should be max. I recommend that you set the Scanalyzer controls using the steps in the second bullet item on page-10 of the article. There are four paragraphs, beginning with "During operation," which detail the tricky setup. The tap for the SB-620 should generally come from the plate or collector of the mixer which is driven by the receiver's variable frequency oscillator. What receiver do you have and where did you place the tap?

Posted by DALE HEIDNER

November 01, 2013 - 12:31 am

i HAVE A PIP, BUT DOES NOT SCAN. how do I get it to scan the band. I must be hooked up to wrong mixer.

Posted by Steve L.

March 14, 2010 - 09:41 pm

Reply to unnamed poster of 3/2/10: Thank you for the compliment and for the comments but I disagree with a few points. I was aware of the "spectrum analyzer" mode of the SB-620. That isn't a good solution here, because it requires an external oscillator, has no bandpass filter ahead of the V1 mixer to reject image frequencies and the load resistance presented to the receiver tap is much lower, resulting in more attenuation. The amplifier is not in the wrong place. It is a wideband amp (for simplicity) and should be after the 620's bandpass filter to minimize problems with interfering signals. It also needs a high-Z load to maximize its gain. It is a good idea to use low capacitance cable for the connection. However, RG62 is listed at 13.6pF/ft versus 20.5pF/ft for RG59. That would increase level only about 3-4dB, which would not be enough to relieve the problem. The amp would still be needed. Again, I appreciate your comments and the stimulating discussion.

Posted by

March 02, 2010 - 01:29 pm

Nicely done. However, unnecessary. An easier modification involves leaving the SB-620 as-is. Move S2 to the 'Spectrum Analyzer' position. This changes V1 from an amplifier to a mixer. You then supply a heterodyne frequency to J1. This frequency would need to be... 3395 + 455 = 3850 KHz or 3395 - 455 = 2940 KHz This will produce 3395, 3850/2940, and 455 KHz at the plate of V1. Even as simple as it is, the bandpass filter between V1 & V2A has sufficient selectivity to reject the other frequencies. The amplifier is in the wrong place. It should be placed at the receiver's mixer (ahead of any selectivity), with light coupling to the source. A common mistake is to ignore the instructions in the SB620 manual that state to use RG62 cable to interface the SB620. This cable has less capacitance, forming less of a voltage divider w/ the coupling capacitor on the input end of the cable. Less attenuation equals less gain downstream. Again, nicely done but unnecessary.

Posted by Steve L.

February 13, 2010 - 08:48 pm

Hi SteveK, My objective was to get a scanalyzer which I already had lying around, to work with a newly acquired Heathkit SB-301 receiver. Both items are vacuum tube, vintage stuff. I suppose there are newer such analyzers but I'm not familiar with them. I always thought of the SB-620 as being a strange, unique product. So I was motivated to restore it. BTW, the SB-301 receiver is the same one as used in the movie, Frequency, with Dennis Quaid :)

Posted by Steve K.

February 13, 2010 - 08:03 pm

What was your objective with this project? Were there other options, such as buying a newer analyzer?

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