[AMRadio] Re: How can we rid the HF bands of AM ?


Patrick Jankowiak recycler at swbell.net
Wed Aug 10 22:25:27 EDT 2005


Hey Geoff,

You are right, I won't be totin' the Tucker KW or even the BTA-250.. For 
me the AM is a hobby and a love for doing things in one of the old and 
respected ways. No General yet, maybe soon. I have alot of fun just 
fiddling with them.

The Transmitters/restorations are on hold as I am doing a major 
clean-out of my lab. Each weekend we have been hauling 800 lbs of junk 
to the landfill, it is -most- politically incorrect. nothing of interest 
here, unless someone wants old 9-track computer tapes and stuff like that.

For what was lost, well that is true to a degree and 3 or 6 dB does not 
make that much difference at the other end, but I guess I am looking at 
the old Tucker rig and knowing its audio and RF power supplies are good 
for 3KW DC each. COL Tucker built it for military communications from 
Dallas to Austin. I mean, the thing was/is capable of who knows how much 
audio input on top of the KW DC. I'm thinking of the peak power. It just 
seems a shame to idle it out along the wireless in 2nd gear. The upside 
is that it will probably last forever.

The status on that beast is that there is a parasitic oscillation in the 
final's grid circuit, between the 4-1000 control and screen grids, at 
about 140MHz. Plate tuning, current, and neuralization setting do not 
matter or vary much at all with this issue and the grid current and 
screen current interact alot. I found that a 50 ohm resistor in series 
with the grid helped. Maybe I need to increase that value or I don't 
know.. The screen grid is heavily bypassed directly at the G2 terminals 
on the socket, and an RF choke is optionally in series with the screen 
to the chassis connector to no effect. This oscillation happens no 
matter if the grid drive connector is shorted, open, or terminated, so 
this tells me it is in the control grid circuit somewhere. Nothing's 
been changed from the original design there, so it is further mysterious.

Also, I need to rig a 220V 30A outlet and power cord for it. I keep 
popping the 120V breaker when running up the final and modulation sides 
together (the unit has two 120V plugs presently).

As far as audio, I'm willing to help anyone who wants better quality 
sound from their AM rig. I'm not a great RF expert at all but I am OK 
with increasing the fidelity/reducing distortion in audio amps.

At this moment I'm limited to NVIS type antennas, but I have a tower to 
put up. another project. I hope a tower will get me better shortwave 
listening due to a higher antenna (and give me a place to put a 6M beam 
for FM).

Patrick



From: Geoff <w5omr at satx.rr.com>
Subject: Re: [AMRadio] Re: How can we rid the HF bands of AM ?
/\/\
If there's an emergency, you -certainly- won't be totin' yer RCA BTA1R
out to a tornado/hurricane/(un)natural disaster site to setup emergency
communications... and the remote site surely doesn't lend itself well to
the kind of power requirements needed by an AM transmitter of any heft.

The way *I* see it, we only lost 500w.  Run your AM rig at 500w DC input
to the final, and let the audio fall where it may.
Perhaps some of the guys on the air will get more interested in making
their final more efficient - find better ways to modulate their rigs -
get some of the trashier sounding rigs off the air, by -helping- that
ham with working on -his- rig.  Get the ol' commraderie going, again.

I can build stuff... I just need to have someone around to talk to, joke
with, laugh at.. er, with (hehe) .. I'm just not a good self-motivator.
Besides, working a project together is what fosters friendships and
forges bonds that keep you tied in a hobby together, for a lifetime.

Speaking of which, Patrick... you ever get your General Class license?
I can't -wait- to hear some of that Big Iron you've got up there, on the
air.


---
73 = Best Regards,
-Geoff/W5OMR



More information about the AMRadio mailing list

This page last updated 23 Oct 2017.