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SWEEP testing a radio from the Mike jack.

Jun 4th 2012, 04:57

KM3F

Joined: Mar 6th 2008, 13:50
Total Topics: 0
Total Posts: 0
I intend to do a sweep test of a SSB radio by driving the mike jack input with a sweeping audio signal, triggering a scope and looking at the RF output display shape.
Iv'e done this many years ago by hand using a wattmeter and was successful in telling me what the relitive band width of the radio was to the half power points.
From this I made audio corrections to fill in the bandwidth the filter would pass and how much Mike response could be used.
This time an EQ will be in the mix to see what can be done after the base response is seen.
Jun 4th 2012, 18:00

K0BG

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
With just one audio frequency, you're not going to see anything worth measuring.

What you really need to be looking at is the third order IMD, and you almost need a complete set of lab equipment to do it correctly. A simple scope just won't show you what you need to know. In fact, most of the time, IMD can be heard long before it shows up on a scope, especially a station monitor.

Jun 4th 2012, 21:36

W0BTU

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Quote by KM3F
... From this I made audio corrections to fill in the bandwidth the filter would pass and how much Mike response could be used.
This time an EQ will be in the mix to see what can be done after the base response is seen.

It sounds like you're trying to get a flat response. Is that correct? A flat response may be OK if you have a strong signal into all the stations you're working. But when you're hardly moving the other guy's s-meter or there's lots of interference, you want to decrease the lows and accentuate the highs. http://www.w0btu.com/ssb_audio-weak_signal.html explains what I mean.

73, Mike
www.w0btu.com

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