John E. Coleman (ARS WA5BXO) wrote:
Mine used to run some of those tubes but I modified it to use some vertical
output tubes from the TV repair days. The speech amp is not required to
deliver any power to the modulator as the modulator is AB1 and even in the days
when I once needed more audio and ran the modulator AB2 the solid state driver
did all the work of grid current. The plates of the Bogen output tubes or
capacitively coupled to the grids of the four 813s and a center tapped choke
feed the bias to the grids
Needless to say, that rig sounds good, when it's on the air.
I need to see what I can do, to secure a remote transmitting site, for
my rig. This latest road-trip has afforded me the opportunity to listen
to some of the late-night operation that occurs on 3.880 and 3.885
(where the bug-catcher is tuned) and I'm hearing -BIG- signals from the
likes of K4KYV (good to hear you on 75m again, Don!), W5JO and welcome
back to the airwaves, Brian/W5AMI. That Flex radio with the Henry amp
is a killer combination from North Central Arkansas! Can't wait to hear
how it's going to sound on 40m today, at 11:00am, CST, on 7.200Mc. Rest
assured, as good as you say my mobile signal was last night, that
antenna works -so- much better on 40m. I grow anxious in anticipation.
I need to get back on during the evening hours, but being besieged with
'neighborhooditis', I don't dare fire up even a 200w signal from the
homebrew rig, less I envoke the nightmares of the neighbors coming down
the street with a bucket of hot tar, a sack full of feathers and a noose
for which to hang me from the yard-arm on my tower! ;-)
Don, and John (and all the rest of us 'technically minded individuals')
While it might be a bit late in the game to petition the ARRL for a
change to the Radio Amateurs Handbook, I wonder if it's worth pursuing
having the book changed. Because, while it's true that to modulate an
AM carrier to 100% with a sine-wave, you only need 50% of the total
final output power in the modulator, the same can -not- be said for
'voice' modulation of the same carrier. Meaning, if you had a 1000w
carrier, in oder to modulate it to 100% wiht a sine-wave, you only need
500w of audio power. But, as evidenced by the research and development
by WA5BXO, K4KYV, WA3WDR and W5TOB, when modulating the carrier with
complex voice patterns, one needs to have, typically, 4x the amount of
power available in the modulator than the carrier presented. This
allows for the natural asymmetrical peaks in typical voice
characteristics to fully modulate the carrier, without flat-topping
causing splatter, distortion and buckshot up and down the band.
If you're unfamiliar with what I'm speaking of, check out
http://w5omr.shacknet.nu:81/~wa5bxo/asyam/Amplitude%20Modulation.htm or
http://www.qsl.net/wa5bxo/asyam/aam3.html
Anyway, with the influx of 'new-to-AM' hams, by digging in the
handbooks, what little information there is on AM does not include
anything of the likes, as what's discussed in the website(s) mentioned
above.
The rain has finally let up a bit here in Baton Rouge, LA. I'm hoping
for good conditions on 40m late this morning.
--
Driving your AM Rig without a scope,
is like driving your car at night, without headlights. (K4KYV)
--
73 = Best Regards,
-Geoff/W5OMR
