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Old 24-Jun-2017, 11:27 PM   #2
rabbit73
Retired A/V Tech
 
Join Date: Aug 2012
Location: S.E. VA
Posts: 2,747
I found some of the original Channel Master 94444 baluns and was able to make measurements of three different baluns. I connected two of each, 300 ohm to 300 ohm, and measured the loss at three frequencies in the UHF band.



For the first measurements, I used a Blonder Tongue HAVM-1UA Frequency Agile Modulator as a stable signal source, and a Sadelco DisplayMax 800 Signal Level Meter. The modulator puts out an analog signal; I used the video carrier for each channel. The Sadelco meter has 0.1 dB resolution.



I was having a problem getting consistent measurements. The Sadelco meter has a built-in calibration reference and at certain intervals will correct its readings. This was difficult for me to deal with when making 0.1 dB resolution measurements, so I switched to my Sadelco 719E meter that has a panel meter with wide 1 dB divisions in the center of the scale that allows me to interpolate to the nearest 0.1 dB.

The Sadelco 719E is on the left; the DisplayMax 800 on the right:



I used the red divisions and the second scale -10 to +20 dBmV.



I would read that as +2.8 dBmV.

To make a measurement, I first connected the modulator to the meter with an F-81 adapter and took a reading. I then substituted the balun pair for the adapter for the second reading. If the loss of each balun is the same, then the loss of one would be half of the pair connected together.

There was an attenuator at the output of the modulator and at the input of the meter to try to keep the line "flat" (low SWR).

Code:
Loss of Three Different Baluns

Ch       Winegard                Channel Master           Channel Master
         TV-2900                 Original 94444             New 94444
          
     F-81  Bal  Dif  Ea       F-81  Bal  Dif  Ea       F-81  Bal  Dif  Ea
     --dBmV---  ---dB--       --dBmV---  ---dB--       --dBmV---  ---dB--

15   7.2   1.5  5.7  2.9      7.2   5.5  1.7  0.9     7.2    1.9  5.3  2.7

28   6.2  -1.0  7.2  3.6      6.2   3.2  3.0  1.5     6.2   -2.6  8.8  4.4

45   5.3  -1.3  6.6  3.3      5.3   2.6  2.7  1.4     5.3   -3.8  9.1  4.6
The Original Channel Master 94444 is clearly the best.
Attached Images
File Type: jpg 3BalunsMeter.jpg (85.2 KB, 5620 views)
File Type: jpg 3Baluns1.jpg (152.2 KB, 4156 views)
File Type: jpg DisplayMaxImg1 (3).jpg (100.4 KB, 4581 views)
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Last edited by rabbit73; 25-Jun-2017 at 2:33 AM.
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