Two each of the test baluns were purchased from an online seller of TV accessories. The subject baluns were tested for insertion loss using the conventional back-to-back method utilizing an HP8569B/8444 combination. Each balun pair was installed into the same fixture (a DB2/4 balun box) so that there would be no difference in the layout of the 300 ohm side of the baluns. Each pair was swept from 50 to 1,000 MHz and the resulting plots were overlaid on a grid representing the scope's graticule. The scope's text display and a legend was added.
Each graph represents the frequency response of a PAIR
of baluns. If each device of the pair were identical, the insertion loss of a single device would be half the measured value of the pair. Since there are variations in devices, this should be accepted only as a genera idea of how each device performed, but, due to the lack of a significant sample size, should NOT be extrapolated to the larger population of devices under the same model number from the same manufacturer. A much larger sample would be needed to identify any trends. Anyone who publicly attempts to make a reach based on this limited data set will be severely chastised.
Reading the plots
The center horizontal line is the 0 dB reference. Each additional line below the middle line represents 2 dB of insertion loss at an given frequency. The center vertical line represents a frequency of 500 MHz. Each vertical line one both side of this line represents 100 MHz difference in frequency. Therefore, from the left, the first vertical line after the border represents 100 MHz, the second 200 MHz, and so forth. Anything under 50 MHz as shown on the plot should be ignored as it is below the operating range of the equipment and there will be anomalies in that part of the graph.
Keep in mind that the equipment used is only able to represent the baluns' response as a scalar value. It is not able to measure complex values related to phase or impedance variations.
As a comparison, ten pairs of the balun/PCB that we use in the C5 were tested and the results are shown below. This balun was selected for superior high-VHF response with as good of UHF response as we can get. They are hand-assembled, so there is definitely some variability in the batch that is apparent in the UHF band.
Discussion is now welcome!