[1000mp] RE: 1000mp Digest, Vol 30, Issue 24

[Rob Murray]

Hi Mike

The perceived advantage was a match that would remain constant independent
of band - and as the toroid only needs to small, I'm not sure that finding a
place for it will be difficult - I admit that I haven't done it yet.

Although as someone else has said one experiment is worth a thousand
something elses, I do not yet understand why a specific length of coax can
be a panacea solution for all frequency inputs - if it is, I can only
suspect some unusual input losses, perhaps meaningless as the exciter has
more than enough oomph to drive the amp anyway. 

I'm sure the coax solutions works - it's just that I hate to apply a
solution to a problem without understanding the why and how. 

For instance, I'm at a loss as to why the coax would be an advantage when
added to an already near perfect (toroidal) match; the phase shift you talk
about is on the output side of the amp relative to the transceiver output,
is it not? Isn't the input side of the amp effectively unshifted? ( can see
the instability problem if there are two tuners in series, each with a large
phase shift, and some spurious feedback path, but I don't see it as a
problem at all with only one major phase shift in the line)

Again I ask, what am I missing - I just plain don't understand.

Robert Murray    VA7RMM
RR1 S5 C16
Edgewood, BC    V0G 1J0
Phone/Fax (250) 269-7698
 
> Message: 8
> Date: Tue, 24 Oct 2006 10:18:38 -0400
> From: "Mike Schatzberg" <cherokeehillfarm at earthlink.net>
> Subject: Re: [1000mp] MK 5 Driving Amp - a twist?
> To: "All about Yaesu 1000mp" <1000mp at mailman.qth.net>
> Message-ID: <012101c6f777$4d7f6000$6601a8c0 at mike>
> Content-Type: text/plain; charset=iso-8859-1
> 
> Hello Rob:
> 
> There are a few amps out there with toroidal input.  They 
> still seem to
> benefit greatly from the Collins approach.
> 
> I am a little confused about the difficulty difference 
> between winding and
> installing a toroidal impedance matching transformer, versus cutting a
> length of coax.  I would think that you might want to take a 
> little time,
> and start with the 23 foot length of coax and prune for 
> lowest SWR.  By the
> way, the resulting solution length of coax can be coiled up 
> for convenience,
> it does not effect the solution, or the resulting phase shift.
> 
> Then if this method fails, you can then redesign the input of 
> your Dentron,
> finding room for the toroid, winding it, installing and testing.
> 
> Perhaps you could then share the results of the two methods 
> with the folks
> on the reflector.
> 
> 73 and Happy DXing,
> 
> Mike
> W2AJI
> ----- Original Message ----- 
> From: "Rob Murray" <rmmurray at xplornet.com>
> To: <1000mp at mailman.qth.net>
> Sent: Tuesday, October 24, 2006 9:58 AM
> Subject: [1000mp] MK 5 Driving Amp - a twist?
> 
> 
> > I have been following the exciter/amp interface thread with great
> interest,
> > and have learned a lot from it, thank you all. I have a Mk 
> 5 driving an
> old
> > Dentron MLA-2500 full power amp, and on reading much 
> earlier in this forum
> > that the Mk5 internal tuner did not add much to the 
> process, discontinued
> > using that tuner.
> >
> > This leaves me with pretty much a permanent SWR at the Mk 5 
> of about 1.8,
> > independent of band choice; I haven't worried about it 
> much, but have
> > thought it would be nice to get it lower. While the thought 
> of the 20.5 ft
> > coax matching section is most interesting, I had been 
> thinking of simply
> > winding a toroidal impedance matching transformer (say 
> N1/N2 = 1.4:1) and
> > placing it somewhere in the input line of the amp (on the 
> amp input side
> > after the bypass relay). This thinking based on the thought 
> (guess?) that
> > the amp input impedance is pretty well set by the 100 ohm 
> input swamping
> > resistor, slightly reduced by the tube input, ie., about 90 
> ohms resistive
> > (generally), consistent with the Dentron specs in the manual.
> >
> > Since none of the discussion has considered such a 
> solution, I must be
> > missing an important point (or two or more...)
> >
> > What am I missing?
> >
> > 73
> >
> > Robert Murray    VA7RMM
> > RR1 S5 C16
> > Edgewood, BC    V0G 1J0
> > Phone/Fax (250) 269-7698
> >