Cecil Moore wrote:
Roy Lewallen wrote:
Why does this seem so complicated?

The SWR bridge circuitry may not correctly display the
actual SWR. Please see my latest response to Tarmo.

The SWR bridge samples the current and voltage and
performs a phasor addition and subtraction to get
voltages proportional to the forward and reflected
powers. If there is a high voltage caused by reactive
components, it will be close to 90 degrees away from
the current. But phasor adding these two values gives
something slightly greater in magnitude than the high
reactive voltage. That high voltage gets rectified and
displayed as the forward power when it is not actually
the forward power but reactive power flowing from one
reactance to another.

Even in this unusual situation, the behavior of the meter is completely
predictable, including the incorrect power indication.

Remember that the meter doesn't actually measure power - it is only
*calibrated* to *indicate* power. When placed in a situation where its
calibration is not valid, then of course it won't indicate power
correctly. But even its wrong indication can be predicted if you know
the detailed values to plug into a circuit model.

There's really no mystery about it.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Ian White, G3SEK wrote:
Even in this unusual situation, the behavior of the meter is completely
predictable, including the incorrect power indication.

There's really no mystery about it.

My point exactly! So, in the same vein, can the source impedance
adversely affect the SWR meter reading?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Cecil Moore wrote:
Ian White, G3SEK wrote:
Even in this unusual situation, the behavior of the meter is
completely predictable, including the incorrect power indication.
There's really no mystery about it.

My point exactly! So, in the same vein, can the source impedance
adversely affect the SWR meter reading?

It will affect both the forward and reverse readings, but in equal
proportion, so it won't affect the indicated or calculated SWR (unless
there are nonlinearities in the meter, or the meter is not being used
correctly).


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek

Ian White, G3SEK wrote:

Cecil Moore wrote:
My point exactly! So, in the same vein, can the source impedance
adversely affect the SWR meter reading?

It will affect both the forward and reverse readings, but in equal
proportion, so it won't affect the indicated or calculated SWR (unless
there are nonlinearities in the meter, or the meter is not being used
correctly).

How about what Chipman says?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----