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Author Topic: Noise Blanker for old TT Argosy  (Read 160 times)

KE4EZ

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Noise Blanker for old TT Argosy
« on: August 27, 2021, 09:54:59 PM »

Anyone have suggestions or circuit I'd like to make a noise blanker for my Ten Tec
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K7MEM

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Re: Noise Blanker for old TT Argosy
« Reply #1 on: August 28, 2021, 02:26:55 AM »

The Ten Tec Argosy has a add-on noise blanker, the Model 223A. The schematic is available, but replicating it would be difficult. I also doubt you will find one for sale.

The most popular noise blanker to use as a add-on for older radios is the Heathkit SBA-104-1. These work very well and sometimes pop up on E-Bay. But they are fairly rare.

About 10, or more, years ago I added a home brew noise blanker to my Heathkit HR-1680 receiver. I found the suggestion for it in an old article in Ham Radio Magazine (April 1976). The article was about miniaturizing a receiver, but it included a simple Noise Blanker that used a MPF-102 FET and a few diodes. So I took the Noise Blanker design and adapted to my radio. Here is a few links to some information.

This first link is to the schematic of the HR-1680 Noise Blanker, showing where I inserted it in circuitry. It is inserted in the IF chain just before the crystal filter.

This next link is a image showing the Perf-Board Layout. This is the layout of the circuit. The terminals with the black "X" are ground connections on the bottom of the board. This fit in nicely in the radio and can be easily removed.

Note that there is no level control or on/off switching. A level control can be included by adding a variable resistor to the gate of the FET. An on/off capability can be effected by putting a SPST switch in the Source lead of the FET. I always intended to add these controls to my HR-1680, but I couldn't find a  good way to add them, without drilling some holes.

Overall, the Noise Blanker worked very well. I still have the radio that way.
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Martin - K7MEM
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KL7CW

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Re: Noise Blanker for old TT Argosy
« Reply #2 on: August 28, 2021, 12:33:52 PM »

As Martin suggested, noise blanking, is best done before filtering.  However perhaps 40 or 50 years ago I successfully greatly reduced (not eliminated) some impulse noise with back to back diodes across the headphones.  I do not remember if they were silicon or germanium.  For sure they mostly took care of a loud click when I switched from TX to RX.  There was no serious distortion at my listening volume.  I do not remember if they worked on electric fence noise, but doubt that would be effective on modern SMPS type noise.  This scheme was very poor in comparison to a "real" noise blanker. At one time we had many electric fences and the noise blanker on my ten tec Omni 6 was so effective on this type of noise, I usually did not even go around to our horse owning neighbors to "fix" their arcing electric fences.  If you cannot build or buy a noise blanker, the diode scheme is just something to try if you have diodes in your junk box.     Rick  KL7CW   Palmer, Alaska
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N8YX

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Re: Noise Blanker for old TT Argosy
« Reply #3 on: August 28, 2021, 01:10:03 PM »

There's an article floating around the 'Net which details using the noise blanker from an SB/HW-104 in an HR-1680, since they share a bit of "DNA" (in the IF strip, particularly). I'd given some thought to doing this. I'd also given some thought to replacing a lot of that radio's IF and AF sections with the boards from a defunct SB-104. Might be an interesting project for some rainy day.
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K7MEM

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Re: Noise Blanker for old TT Argosy
« Reply #4 on: August 29, 2021, 12:15:35 AM »

The back-to-back diode scheme works fine in some cases. It's a good thing to try first. But it is just a "clipper". The noise is still there, just clipped and at a lower level.

The article that uses the SB-104's Noise Blanker was in the January 1980 issue of 73 Magazine. It's readily available on the internet. There were several other articles about the HR-1680 at the time. There was always an article trying to make a good thing better.

I was working in Germany (DA2EU) at that time (1980) and bought the whole HR-1680/HX-1681 combination (complete with HS-1661 speaker and HD-1410 Keyer). I found that the setup worked great. I loved operating Full QSK. I mostly worked 15 Meters and had no problem working stations all over England, Europe, Asia, Africa, etc.. For a while I had my Commodore 64 hooked up to it. The 64 ran a CW RX/TX program that came from a 73 Magazine article.

I didn't have any issues with noise, until I returned to the US, a few years later. That's when I started thinking about a noise blanker. But life got in the way and didn't actually build one until many years later.

The only thing I didn't like about the HR/HX setup was when the other operator asked what kind of rig am I using. I usually tried to simply say "heathkit", but they usually wanted the whole descriptor. It was a real pain tapping out "HR-1680/HX-1681". Because the unit was new and not very popular, most ops didn't know what it was anyway.
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Martin - K7MEM
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