Topband: Two Wire Beverage Query...

[Ford Peterson]

Interesting results...  Good, solid data confirming ON4UN's table 7-10 info.

After taking Tom's advice and choosing to measure the impedances correctly (i.e. lashing the two wires together at each end), I have pretty convincing evidence that my termination impedance should be about 353 ohms.  Since I wound it for 450 ohms, perhaps this also explains why my feedpoint impedance consistantly comes in at 40 ohms at most frequencies below 8MHz.

Term      Measured
Ohms    Min    Max    Sqrt(RminRmax)  Range   Error
340        338    372          355                 34        15
351        340    367          353                 27          2
360        335    363          349                 28      -11
379        327    370          348                 43      -31

My best guess based on this is 353 ohms.  This appears to be consistant with Table 7-10, which used meters intead of 9 feet and 12" spacing (710 ohms) instead of my 10" spacing (688 ohms).  So my termination transformer will get wound as close to (688 : 353) as I can get.

By the way, using the Autek VA1's 300 ohm mode, it was difficult to sweep and document the variation in SWR since all of the above values never fell outside the 1.14 to 1.24 SWR relative to 300 ohms.  So the Square Root of the Minimum times the Maximum reading over frequency was the best of the two approaches.  In all the measurements, I swept from 600 KHz to well over 8.4 MHz.  The data started to fall apart at about 7.5 MHz, so I limited my sweep to about that spot.  None of the above data points were any where near either frequency extremes.

Thanks for all the help.  I can now fix my beverage and forget about whether it is 'right' or not.  Problems in pattern will no-doubt be sourced to other issues, rather than termination design.

Ford-N0FP
ford at cmgate.com