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Re: LF: More on Admittance

To: [email protected]
Subject: Re: LF: More on Admittance
From: Peter Dodd <[email protected]>
Date: Sat, 22 Nov 2008 20:07:13 +0000
In-reply-to: <[email protected]>
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Hi Alan,
Thanks for the information. Most noise bridges use serial variable resistance and reactance bridges but there is a circuit of a bridge using a parallel arrangement in the W6SAI radio Handbook although it doesn't say what the advantage of such an arrangement is.

Regards

Peter, G3LDO
Hi Peter I think it more due to the fact that commercial bridges and meters 
really want to cover the widest range. There is obviously a problem with serial 
connected reactances when one is very much larger than the other. Then the 
nulls on bridges become shallow and ill defined. If you use a parallel 
arrangement this is not a problem. For most Amateur aerial cases you can get 
away with serial connection because there is not the need for the wide range 
needed for laboratory equipment.....10^3 compared with maybe 10^6.

Alan G3NYK




--- On Wed, 19/11/08, Peter Dodd <[email protected]> wrote:

From: Peter Dodd <[email protected]>
Subject: LF: More on Admittance
To: [email protected]
Date: Wednesday, 19 November, 2008, 6:55 PM
Many thanks to those who responded to my question regarding
an Admittance to Impedance converter.
I have a further question. Since most of the measurements
we make on antennas and transmission line require the answer in term of impedance why are there so many commercial instruments calibrated in units of Admittance, particularly at VHF and UHF. I suspect that it is because it is easier to make accurate variable bridge standards if they use a parallel arrangement; is this true
Regards

Peter, G3LDO


The best program (as far as I am concerned) is called
Z-Y Converter,
which was sent to me by Rik Strobbe.
It came direct because it gave the reflector
indigestion although it
is only 160KB.
I was given a General Radio 1602-B Admittance Meter as
a pre Christmas
present, which is calibrated in millimhos, which I
guess is the same
as millisiemens.






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