[AMRadio] Dentron Clipperton on am?..

Tue Apr 12 15:14:49 EDT 2011

I agree with you Jim on the 375 watt output is safe in just about all cases.

To answer someone else's question about SB power of AM when an asymmetrical
modulation envelope is inverted.

	It is easy to understand in a high-level modulated rig.
If you look at the plate voltage while it is modulated you can see what is
happening.
IF the modulation level, audio drive, modulator output power, whatever you
want to call it, is the same in either case, and you don't over modulate
(send the plate voltage negative on a spike),then the sideband power is the
same. The asymmetrical wave of audio is short time on the spikes and long
time on the lower level stuff. So even though the tall spike is a high peak
power its average power is the same as the lower level part of the wave.
The lower level part of the wave has a lower voltage but is there for a
longer time so over the whole wave envelope it makes no difference as to
whether the wave is inverted or not, it still has the same average power of
audio and side band power

	But here is the difference.  If the audio is asymmetrical and you
are modulating a rig at the 100% level on the wide troughs of the audio wave
almost pinching the carrier, and perhaps tripling the voltage on the spikes
peak, and then you invert the audio you will clip the carrier
(overmodulate).  This is easily compensated for by raising the plate voltage
on the final amp until the now downward going spike is no long over
modulating.  You will be increasing the carrier level while keeping the
audio level the same.  The carrier power will go up but the sideband power
RF will still be at the same level that it was before inversion. And the PEP
power of the rig will still be the same even though the carrier power is
greater.

	None of this really has a thing to do with having fun on AM.  It
takes very high -fidelity speech amps and modulators to get the microphone
audio wave to be duplicated at the plate of the final.  Way more trouble
than most would say it is worth.  But it was fun experimenting and learning
for me.

	To do these experiment I had to build extreme hi-fi all the way
through the final with no audio frequency compensation circuits for low or
highs.  I had to pass frequency as low 20 CPS, un-boosted though.  I had to
have separate power supplies for the final and the modulator.  The final RF
plate supply had to be on a big variac.  I had to have a way to hold the
modulation level constant. And I had to have a way to make the inversion
switch.

	As I said it was a pain but I like that type of thing.  I could have
done it more easily at a lower level that a KW but at low power it is some
time hard for a listing station with scope monitoring to see what I see and
my scope so high power was what I did.

Thank for reading.
John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jim Wilhite
Sent: Tuesday, April 12, 2011 11:30 AM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Dentron Clipperton on am?..

I have an LP 100 and can attest to their ability.  In fact when I 
received it, I was surprised that it showed some transmitters to have 
greater PEP output than people said and low output on peaks on other 
equipment that people hail as good transmitters.

In relation to being  correct about modulation Gary presented a very 
easy to understand explanation.  If you have access to a spectrum 
analyzer you can see the sideband power.  You look at the AM signal and 
modulate it.  You will see the sidebands pop up on either side of the 
carrier.  The carrier will have a sawtooth look to it which is the 
modulation riding on the carrier wave.  When you quit speaking the 
sidebands will disappear like a SSB signal does on a monitor scope.

Some where around here I have a very old book, I can't even remember its 
name, that gives all the analysis and how to calculate what you want 
Kim.  Gary can also do those calculations, but for a weak math person, 
they are difficult to understand so if you want to connect with him I 
suggest you go direct.  Most of us would be lost quickly.

The FCC won't go into this much, in fact they routinely overlook people 
who are running much more than 1500 PEP.  The offenders, if you wish to 
call them that, who do not cause trouble for anyone will be ignored 
besides the FCC is very busy auctioning off the 420-450 Mc part of our 
spectrum, so they don't spend a lot of time with us.  They will make off 
air measurements, if you have a very bad or long series of complaints, 
with equipment that will tell them what you are doing and they don't 
have to be in your yard.

If you are concerned about the power you put into the antenna, then run 
350 watts of carrier with either the requisite 100% either positive or 
negative modulation, or both.  This is an easy solution and doesn't 
require expensive peak reading meters.  Incidentally the LP 100 is a 
very good, well constructed piece of equipment.  It shows my Globe King 
500A puts out about 325 watts of carrier and will modulate that to 1250 
watts PEP occasionally on the right syllable.

Jim/W5JO

----- Original Message ----- 

> Why not just use a good peak reading wattmeter and adjust the output 
> to 1500
> watts PEP, no matter what the carrier power is?  Something like a 
> LP-100A
> would be great for this (wish I owned one!)
>
> However, I think that if you use the 4:1 rule, 160 watts carrier is 
> the most
> you would want to run with 4 X 572B's given their 160 watt plate
> dissipation.  Any more than that with any reasonable transmission time 
> will
> severely stress and shorten the life of the 572B's.  If you really 
> blast
> them with air, you might get away with a little more......
>
> Mike WB0SND
>

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