[CQ-Contest] Help making single stubs

Sam Ferris ve5sf at sk.sympatico.ca
Fri Jun 19 05:59:05 EDT 1998

Need some advice from the contest reflector members who may have 
experience with making stubs - I'm sure ther must be lots of you out 
there.  Yes I'm into the final phases of getting ready for our local club 
field day effort and this year some stubs to help more with the QRM 
would be nice.  Only made one so far, a 15 metre shorted 1/4 wave stub 
(actually it started out as a 20 metre version - but you all know what 
happend.....).  The length came out pretty close to what I expected using 
246/F x VF, but I was not able to achieve the desired resolution in 
measurement that I expected using the method that I tried.

In ON4UN's 2nd edition of Low band DX'ing, John describes a method using 
a transmitter feeding a Bird wattmeter, then a coaxial "T" to a 50 ohm 
dummy load on one side and the 1/4 or 1/2 stub under test on the other 
side of the "T".  I was noted that very precise timing could be achieved 
using this method allowing trimming to within a few KHz.  My result was 
somewhat different.  There certainly was a dip in the SWR at resonance, 
but no where near what I would have expected to achieve for cable length 
measurements within a few KHz... maybe a 100 KHz resolution at best.

Anyone else have this experience with this method?  Any suggestions as to 
what I may have done wrong what I can do to correct it or better methods 
of measurement with minimal of test equipment?  The connectors I used 
were UHF style amphenol.  The cable is also good quality RG-213.

Many thanks... 

Sam ... VE5SF

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