[Boatanchors] Re: [FLBOATANCHORS] Re: 160 Meter AM Question -Transverter

[Rodger]

Hi Doc,

For the transverter it would be far simpler just to design for class AB1 for
all modes and accept that you will have to live with lower efficiency and
lower power for AM.  Once amplitude modulation (of any type, AM/SSB/DSB
etc.) you must use linear amplification to avoid distortion (I guess the
"switching mode" amplifiers might be an exception).  Although it was common
in the "early days" to have dual mode finals they do create additional
issues of complexity (switching and perhaps also regulating G1 and G2
potentials).  Also, harmonic generation is greater in a Class C stage so
additional output filtering is often necessary to avoid potential TVI. I
have some transmitters (Johnson Valiant, Heath TX-1, etc.) which switch the
final mode along with Desk KW and Viking Thunderbolt amplifiers which also
switch between AB and C modes but they are quite a bit more complex than the
grounded grid linear amplifiers which became the standard for amateur usage.

If you plan to operate AM only on 160 then it would probably make more sense
to build the transverter as a class C transmitter and then use the existing
transmitter to provide B+ and modulated HV.  In this way, you can use the
power supplies and modulator you already have.  You might use the Johnson
6N2 transmitter as "inspiration".  This transmitter allowed the use of the
Ranger, Valiant, and some other transmitters on 6 and 2 meter CW and AM.
The existing transmitter provided all operating voltages including modulated
HV and the 6N2 provided a fairly straightforward exciter and amplifier
layout.  If you decide to follow this course of action, make sure you do as
Johnson did and disable the high level RF stages in the existing transmitter
when using it as a power supply/modulator for other bands.  Johnson also
supplied filament power to the 6N2 from the main transmitter and switching
over automatically disabled the final filaments in the main transmitter to
avoid excessive load on the transformer.

Good luck with your future experiments and building.

73, Rodger WQ9E  

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of kd4e
> Sent: Monday, January 29, 2007 12:26 PM
> To: FLBOATANCHORS at yahoogroups.com
> Cc: Boatanchors at mailman.qth.net; BOATANCHORS at LISTSERV.TEMPE.GOV
> Subject: [Boatanchors] Re: [FLBOATANCHORS] Re: 160 Meter AM Question -
> Transverter
> 
> > You don't want to run it Class C, as it will distort the SSB signal.
> > To run AM, it would be better to build an exciter with Class C finals
> > and Class B Audio. It would be an inefficient way to run AM using
> > such a transverter, because you would have to drop the drive from 40m
> > to drive the transverter, and then you would be looking at
> > inefficiency of the 6146 as a linear(AB1). Joe W4AAB
> 
> I thought that I had read of designs where a switching
> mechanism would allow the amp to run in Class C or AB1
> mode.  Is the reality that attempting that not recommended?
> 
> So an all-mode transverter either has to run inefficiently
> in AB1 mode or utilize dual TX sections, one for SSB
> and the other for AM/CW/Digital/FM?
> 
> Is DSB likely to be harmed as badly as SSB by Class C?
> 
> I know that I should know that but I don't remember
> what I used to know about that!
> 
> I could consult a Handbook but it is more entertaining
> to have a keyboard-Internet-keyboard QSO.  :-)
> 
> --
> 
> Thanks! & 73, doc, KD4E
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Projects: http://ham-macguyver.bibleseven.com
> Personal: http://bibleseven.com
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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