The AM Forum

Has anybody ever used the K7DYY AM modulation monitor?
If so,what's your opinion?
W9BHI

I did a search and found several posts that nit picked it and then went off topic.
Any real experience with this unit?

Thanks W9BHI

I can see why the nit picks.  There isn't much info on the web site.  I'll resist the urge to not pick myself and keep a lookout for those who have used it and post that info here

Al

I have been tempted to order one in the past.  No info on the website has stopped the order.  In todays day and age, A simple video of the product would almost be a requirement for me. 

C

Plenty of info there for me to know I don't want it.

:-)

Between the specs on the order page, and the pictures in the online 'manual'.

You cannot meaasure your modulation level with it.
It is a unmarked/uncalibrated bargraph that shows positive modulation level.
I suppose that when all the 'bars' are lit, you're at 100%. 

What are your requirements?  It may or may suite your needs depending on what your looking for. 

It appears to be more of a modulation alert than a true instrument to measure percentage of modulation.  It does alert you if you over modulate in the negative direction.  That is a good feature, but if your looking to measure your actual percentage in the positive and negative direction you will need to do some work.  With a scope and a sine wave generator you should be able to come up with a calibrated scale based on the bars that are lit.  It also appears that anything above 100% may not be seen on this monitor.  Some folks like to keep within 100% positive modulation, so for them it may be fine.  In addition it appears you get a low distortion audio detector to listen to your actual transmitted signal. 

I have never owned this device so I have no first hand knowledge in using it.  I would suggest an email to Bruce, K7DYY and see if you can get any of your questions answered. 

I use an REA modulation monitor and think its fantastic.  Unfortunately its no longer available but I heard some time back that Steve developed a software version.  You may send a note to Steve of REA fame! 

Used Belar modulation monitors are available from time to time.  They have been pretty much the standard in the AM broadcasting business for many years.

Good luck in finding something that satisfies your personal requirements. 

Joe, W3GMS       

Looks as if it can only tell you that you have gone past -100% modulation but doesn't state that it will alert you when you have exeeded +100%.
I do like the frequency counter as well as the forward pwr/swr function.
I thought it might be a nice little addition to my Valiant II.

Thanks for the input.
Don W9BHI

I did not see the page about the monitor under his "support" menu.  That seems like an odd place for that information that could be used for sales. 

It really seems like a neat tool.  It does have a negative warning which is important. when a plate modulated transmitter reaches 100 negative its unloaded and very hard on the iron.  Lots of people do not realize this.  Its one reason why I dont like ripping limiters and clipper sections out of these old radios.  The iron is to hard to come by to be damaging things.

I have a power master NIST calibrated meter here and a bird 43P.  But It sure looks like a neat meter to sit next to your AM station.

I have an Array Solutions Power Master meter that is currently connected to my AT-Auto tuner.
At one time Array Solutions was going to incorporate a modulation indicator on their meter but the option never came about....too bad.

W9BHI

If you want a monitor just for negative peaks, get an 866A.
http://amfone.net/Amforum/index.php?topic=27557.0
I also found a circuit in the 1953 ARRL handbook, that uses a high-vacuum rectifier (a mercury vapor rectifier can be used, but there is a 15 volt drop across the tube) with the cathode hooked to the final side of the mod iron, and the negative side of a 0-50 ma milliammeter hooked to the plate. The positive side if the meter is grounded and also has a return line to the negative side of the final's B+ supply. The meter will kick up when the modulator drives the plate of the final negative. So to keep from going over 100% negative modulation, don't let the meter kick up. The inverse peak voltage rating of the recifer must be at least twice the voltage of the final. I'm gonna say a solid state rectifier will also work.

There are some things I like about the schematic and it has a programming port. I'll wait for reviews too.

As for the 866A, try to find an old style 866 which has no filament shield because the display may be better. Beware it won't take as much voltage as the -A but nothing's perfect.

Cool. How does the 866 read Frequency?  Forward power?  Reflected power?  SWR?  Thats really neat,  An 866 that hooks to the coax line of any transmitter.  Cool stuff!

Just kidding.  Neat idea but way off topic here.

C

If your rig already has decent frequency readout and you already have a decent wattmeter, why buy that monitor if the only new thing it would provide is the negative peak monitor? You could make that yourself, hence the reason for my post. If you wanted to build something to monitor negative peaks that would fit in better with vintage equipment, my suggestions would work.