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Date: Sat, 22 Nov 2008 20:07:13 +0000
From: Peter Dodd <g3ldo@ukonline.co.uk>
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Subject: Re: LF: More on Admittance
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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 <g3ldo@ukonline.co.uk> wrote:
>
>   
>> From: Peter Dodd <g3ldo@ukonline.co.uk>
>> Subject: LF: More on Admittance
>> To: rsgb_lf_group@blacksheep.org
>> 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.
>>>       
>
>
>
>