Re: [Amps] 10dB and propagation

[R.Measures <r@somis.org>]

On Feb 7, 2005, at 6:48 PM, Michael Tope wrote:

> ---- Original Message -----
> From: "R.Measures" <r@somis.org>
>
> > On Feb 6, 2005, at 6:09 PM, Michael Tope wrote:
> >
> > > You stole my thunder, Ian. Yuri and Rich seem to be
> > > agreeing with each other about two totally different
> > > things. What Rich was talking about is path loss that
> > > varies as a function of EIRP. In my opinion, this is a
> > > very questionable thesis given the amount of power
> > > involved (even 10dB above the legal limit in the US is
> > > a drop in the bucket - remember we are talking about
> > > microwatts/meter^2 whereas the old sol is in range
> > > of KW's/meter^2).
> >
> > Mike -- Which is why I was originally skeptical.   However, the
> > Stanford Research Institute's ionospheric project used 8171 
> > amplifiers.
>
> Did they publish any papers on this phenomenon?

Yes, but I do not know where it could be found today.  However, the SRI 
project involved heating on one frequency and comparing signal strength 
of a second signal on an adjacent frequency with and without the 
heater.  This was obviously better science than what we did.
cheerz, Mike
> > > 1). Was there any time constant associated with this
> > > "non-linear" phenomenon? If for instance the time
> > > constant of the non-linear effect is faster than say 10mS,
> > > then one could expect it to generate IMD products as
> > > the non-linearity would be within the audio bandwidth of
> > > an SSB transmitter.
> >
> > The time constant was long and was seemingly related to sun angle and
> > serendippity.
>
> What do you mean by long - seconds, minutes, hours?
>
> And by time constant do you mean to say that at the first instant of
> comparison, the instantaneous on/off ratio of the 8171 was 20dB,
> but as you worked the frequency harder, the instantaneous on/off
> ratio changed to 23dB?

 Some mornings, 20db more Tx suds produced 20db more Rx signal and on 
other mornings, 20db more Tx would make c. 23db more Rx signal.  There 
appeared to be no way of controlling anything.  It was: what you see is 
what you got, and you can't change it a jot.
> In other words did the instantaneous on/off ratio of the 8171 change
> as a function of exposure time?

Nope.  Maybe a 30db amp could have done that, but a 20db amp rather 
obviously was not up to the job.  As I see it, a homebrew 30db 
amplifier is not do-able without a 2160v 3Ø mains service and a 
forklift to help build one of the suckers.  Also, some lead shielding 
would be a pretty damn good idea since the anode-PS would be c. 22kV 
@10A -- which is definitely downtown X-Ray City.  Another problem would 
be finding some ABS or TFE owls to put on the antenna to keep birds 
from alighting and having their feet burned off by RF.  Another 
obstacle would be getting a building permit to build a moat and 
drawbridge.
> > > 3). What experimental protocol did the 8171 owner use
> > > to ensure that his power gain was really 20.0dB.
> >
> > The V-gain was x 10.
> > > Old measurements that Rich made in his lab wouldn't
> > > necessarily be valid as the new owner's setup could
> > > easily have added 3dB of uncertainty.
> >
> > Not likely because the mains-V was 240v +/- 5% at both sites and no
> > change had been made in the anode or screen supplies.  I measured
> > 1200V-pk output into 50-ohms (14kW), and my guess is that adding 3db
> > (28kW) was not do-able short of going to an 8281 (4cx15.....), a more
> > capable anode supply, and most likely a 200a mains service.
> > >
>
> What about load VSWR? Did his antenna VSWR match
> the input VSWR of the 8171 amplifier?

It wasn't perfect, but since the driver was a TS-830, it wasn't 
bothered by minor SWR like a solid-state radio would have been.

> If not, then his
> on/off ratio could have easily differed from one you
> measured under different conditions.

The conditions were always a TS-830S driving an AB1 8170.  The 830 
delivered 120v-pk into the dipole.  The 8170 delivered 1200v-pk into 
the dipole.  Sometimes the 8170 delivered a 20db increase at the Rx 
end, and sometimes an additional free-3db showed up.

> And was the tuning
> of the 8171 fixed.

gimme a break

> If not, he may have adjusted the tuning
> differently than you did (another source of possible error).

Jim Day knew how to tune up a Class AB1 amplifier because I showed him 
how b4 he hauled it away.  Basically, AB1 tuneup's done with the 
screen-I meter.

cheers, Mike
> 73 de Mike, W4EF..................................

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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