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AM modulation monitor wanted

R

rickradio

Guest
I'm hoping someone can help me out here. I'm looking for a used AM modulation monitor in good working condition for my Part 15 AM. I almost got a Potomac Instruments on eBay a while back, but the moron who sold it to me had a brain fart and shipped it to someone else after I'd paid for it thinking it was me he was shipping it to (or so he said). He did refund my money, but I still don't have a mod monitor, can't find anything else decent on eBay, BSW's prices are insane because they want to turn a healthy profit on everything they sell, and Radio Engineering Associates, even when begged and bribed, can't be persuaded to build any more of their monitors, even though their website touting said monitors is still up (but saying that they're sold out). Can anyone point me in the direction of one that someone doesn't want anymore and won't charge a price that includes a vial of blood? I'm all I got (I don't have a network bankrolling me). Thanks for any and all help.
 
You might want a mod monitor with meters, but personally my favorite mod monitor has a CRT in it. They can be found at hamfests and surplus stores. It's a O-scope.
 
An O-scope for a mod monitor is much more accurate, too. Might be able to find a small o-scope at a hamfest or something. And that REA mod monitor sure does look like the AM mod monitor that Inovonics used to sell
 
A regular mod monitor for a part 15 AM will need an RF Amplifier...it takes more than 100 milliwatts to drive the monitor. Even if 75 milliwatts (best you could expect from a 100 milliwatt DC input) output did drive the monitor, I doubt you'd want to use all of your signal just to drive the mod monitor :eek:
 
When I do my bench tests with a Belar AMM-3 the companion RF amplifier is a must.

If you have the bucks and can justify it in some other way I often seem the DaySequerra M2 AM and FM analong and HD mod monitor up on ebay for around $600 but I will warn you - their service is the pits! I sent one back under warranty for updates and testing and it came back working but screwed up. I'd personally stick with Belars.
 
rickradio said:
BSW's prices are insane because they want to turn a healthy profit on everything they sell,
Click to expand...
BSW and other major equipment distributors operate on a very thin margin, maybe 10-15%. The cost of new AM monitors is based on the fact that not very many are sold, and they probably are made in runs of less than 10.
 
Bill Wolfenbarger said:
BSW and other major equipment distributors operate on a very thin margin, maybe 10-15%. The cost of new AM monitors is based on the fact that not very many are sold, and they probably are made in runs of less than 10.
Click to expand...

That is quite true. I used to sell some of this stuff. BSW's margins are very "thin." I buy from them myself.
 
A scope is great for seeing negative peaks but without some way to calibrate it with unmodulated carrier, it is hard to read the positive peaks; I use both.

Bob
 
Dr. Bob said:
A scope is great for seeing negative peaks but without some way to calibrate it with unmodulated carrier, it is hard to read the positive peaks; I use both.

Bob
Click to expand...

If it's really a part15 station, the modulation isn't regulated. Use a scope to avoid negative 100% so as to avoid clipping and enjoy. If concerned about positive peaks, just modulate symetrically.
 
A scope is great for seeing negative peaks but without some way to calibrate it with unmodulated carrier, it is hard to read the positive peaks
Click to expand...

If this is a Part 15 AM setup, just disconnect the program input to the transmitter, adjust the vertical gain on the scope for some peak-to-peak value on the screen, and mark those levels on the screen somehow. Then make two more marks separated by twice the vertical distance apart as the first two marks. Of course if the scope has a calibrated graticule then marking wouldn't be necessary.

The scope will show 100% positive peak modulation when the p-p amplitude of the modulated carrier is twice the amplitude of the unmodulated carrier.
//
 
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