[BC] Wanted: Bird Model 43 Slugs

[bob at broadcast-devices.com]

Jeff:
For a model 43 I suspect that the level of accuracy of "just good 
enough" is what the user is probably looking for. Of course you are 
right on with the fact that to get a higher level of accuracy with 
any D.C. elemental slug/line section system special attention need to 
be paid when it is being called upon to measure over a frequency 
range even as narrow as the FM band. Dynamic range of the system is 
also a factor and commonly misunderstood. Most manufacturers of D.C. 
elemental systems specify accuracy as so many per cent of full scale. 
The error level can ratchet up if you are trying to use a 10 kW 
element to measure 3 or 4 kW. Now your 5% of full scale is more like 
a possible 40 or 50% of full scale. A tip I would add is that if you 
are using a D.C. element to measure power make sure you are using one 
that is not only for the frequency range needed but that is a full 
scale rating just above what you are trying to measure to minimize 
error due to the non linear nature of su!
  ch elements.
D.C. elemental systems are largely being displaced by RMS measurement 
techniques due to the fact that diode detectors are not terribly 
linear, bandwidth is narrow as you pointed out in your post and that 
they are really not accurate for complex modulation systems or for 
multi carrier measurements such as in broad band lines from the 
output of an FM/IBOC or TV combiner.
For those interested BDI has a white paper that we distribute free of 
charge discussing various RF measurement techniques as this is a line 
of business for us.  Please  feel free to email me off line and we 
can send you a copy. It occurred to me as I was writing this that we 
should publish this on our web site which we will do in the near future.
All the same you make some very good points about the use of D.C. 
elemental measuring equipment.
Sincerely,
Bob Tarsio
President
Broadcast Devices, Inc.
www.broadcast-devices.com
(914) 737-5032

 >Since we're on the subject, I need a 50-watt 100-250 and a 25 watt
 >400-1000
One thing to keep in mind - if you want accurate results, the slugs 
need to be calibrated to the specific directional coupler and meter 
movement to be used, that's why all of our elements have the serial 
number of the meter/coupler they are to be used with stenciled on 
them. Bird used to do this for a nominal fee (I assume they still 
do), not sure if any other sources do or not, but it's worth 
remembering. Bird would provide error an error chart across the 
frequency range so you always knew what the power was at that 
frequency - at least for that point in the line!
Best,
Jeff
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