Re: [Amps] 10dB and propagation

[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.

> Yuri seems to be making the claim
> that path loss can be a highly variable function of
> location, antenna height, frequency, local terrain, the
> ionosphere, the neutral atmosphere, etc. I certainly
> hope nobody is disputing that. If they are then they
> haven't been on the air very much :):)
>
> In regards to Rich's observations, we need to be
> asking several important questions:
>
> 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.
> 2). What experimental protocol did Rich and his fellow
> observers use to control for fading? Calibrated S-meters
> alone aren't sufficient to control for fading.

Numerous On-Off sequences comparing the signal change with On-Off 
sequences from others on the group who were using 10db gain amplifiers.
> 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.
> 73 de Mike, W4EF.........................................
>
>
> ----- Original Message -----
> From: "Ian White G3SEK" <G3SEK@ifwtech.co.uk>
> To: <amps@contesting.com>
> Sent: Sunday, February 06, 2005 3:30 PM
> Subject: Re: [Amps] 10dB and propagation
>
>
> > Yuri wrote:
> > > You guys might try to poke fun at this. But there are many factors
> > > contributing to signal levels received at the other end. Antenna
> > > pattern, local ground conditions, terrain and propagation conditions.
> > > VHFers know about ducting on VHF between W6 and KH6, you drive up the
> > > hill and you can find spot where your signal (few watts) will hit it
> > > and you QSO with KH6. You go few hundred feet up or down and you 
> > > lose it.
> > Sure, all of that is true... but it all goes strictly dB for dB. There
> > is no support for tropo ducts behaving in a non-linear fashion.
> >
> > Let's not confuse the variable *importance* of a dB under different
> > circumstances (which is obviously true) with any suggestion that the
> > propagation medium itself is non-linear.
> >
> > A non-linear medium would have to mean that your signal was directly
> > affecting the ionization density or the refractive index of the
> > troposphere. As I already said, that's wishful thinking at amateur 
> > power
> > levels.
>
>
>
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Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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