Steve & Vic,
Really good points. If he's using a meter with a simple directional coupler
(e.g., Monimatch, Bruene, Bird Thruline), then I would expect the indicated
forward power reading to increase well above 800W. The better the amp's
output network is converting Z between the PA and line input, the higher the
indicated forward reading.
If the amp output network could tune and match between the PA source and
line input Z, then a loss-less line should show high reflected power with
the forward indicator reading the reflected value + 800.
But there's another possibility. I don't think the originator of the
message thread indicated the type of line being used. My apologies if I
glossed over it. It's possible that a 12:1 SWR exists on the line and yet
have a Z of 50+j0 at the line input by having the right dynamics of line
length, line Zo, and terminating Z. In that case, 800 watts is indicated,
800 watts is really delivered, zero reflected watts are indicated and zero
watts are truly reflected. The SWR on the line is 12:1, but the SWR (50) at
any point between the generator and the line input is 1:1.
Also, I really detest the notion that watts are being reflected -- or
somehow moving forward on a line. Despite being lazy about it myself, it's
probably best to discuss what happening in terms of voltage, current,
forward wave, and reflected wave. Power is an end result of those forces.
It's not moving in any direction.
Paul, W9AC
----- Original Message -----
From: "Steve Katz" <stevek@jmr.com>
To: "Vic K2VCO" <k2vco.vic@gmail.com>; <amps@contesting.com>
Sent: Monday, July 30, 2012 2:06 PM
Subject: Re: [Amps] Al80b
> Bingo. I'd say the same thing.
>
> 12:1 SWR is 42% reflected power and most every "wattmeter" in the world
> measures a combination of F+R when measuring forward power. So if it
> reads 800W, actual forward power is likely 464W (and reflected is 336W).
> Happens with every meter I have. Bird dedicates a page in their Thruline
> manuals about this.
>
> -WB2WIK
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Vic K2VCO
> Sent: Monday, July 30, 2012 10:44 AM
> To: amps@contesting.com
> Subject: Re: [Amps] Al80b
>
> I believe that he is getting some kind of meter to tell him that he is
> getting 800 watts output. I doubt that he is. I don't know of any
> commercially available wattmeter that is accurate when the SWR is so high.
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|