• Bow Tie Antenna Angle Tests



    This is the last article in the series of bow tie (BT) antenna tests. In this test, the angle used, or put another way, the separation distance between the two ends of the BT "V," was changed to see what effect this had on the signal levels of the various TV channels.

    The approximate separation distances and approximate angles used were:





    Each pair of elements was attached to the BT antenna mount and all tests were run for that antenna. First, a set of readings for the standard angle of approximately 22 degrees, then the angle was change to approximately 36 degrees and another set of readings was taken, then the last angle change was made to approximately 50 degrees and the last set of analog signal level readings was taken.

    These tests were all made without the transformer being used. The repeatability tests showed that we cannot trust anything less than 1.1 dB difference. Anything below that could be in the noise, so we need to ignore all changes below 1.1 dB.


    The data for the 8" BT is listed below:





    It can be seen that for the 36-degree angle there was only one station with an improvement of more than 1 dB, while there were five stations that were better off at 22 degrees, three of which were better than 2 dB. Also, notice that there is no overall shift to indicate that the change had any affect on the frequencies in any given range. The differences of the stations between 22 degrees to 50 degrees was just as uneventful; here there were three stations that improved more than 1 dB and three stations which were better off with 22 degrees. Again, these stations for both angles are scattered, 7, 36, and 46 better for 50 degrees and channels 29, 35, and 50 better with 22 degrees.

    I think it is safe to conclude that for the 8" BT, changing the angle does not seem to have a marked affect on the frequency response of the antenna within the TV frequency range.


    The data for the 12" BT is listed below:





    Here we see four stations improved using the 36 degree angle by more than 1 dB, of which only one was a very substantial change of 4 dB. The 22 degree angle was better by 1dB for also four channels but the best was only better by 2.3dB. The channels seem to be scattered for both the 22 or 36 degree improvements. For 36 degrees, the improvements were for channels 13, 24, 38, and 40. It looks like I should have included channel 39 to see if this was a small three-channel grouping. The channels better for the 22 degree angle were 29, 33, 41, and 46, and here there were no stations between 29 and 33 to include to see if this were a five-channel grouping or not. So for now, I think that there is no reason to use 36 degrees rather than 22 degrees.

    As for the 50-degree angle, we have seven stations that were better than 1 dB improvement and, again, channel 50 was the best at 3.8 dB. This is starting to look like a trend. There were four channels that were better using the 22-degree angle and the best was an improvement of 2.5dB. For 50 degrees, the channels were 13, 24, 29, 38, 40, 48, and 50. For 50 degrees, the best was channel 38, and for 22 degrees, the best was channel 33 which is different than for the 22 to 36-degree change.

    All that can be said is that some improve a little and some degrade a little; there were no significant improvements or insignificant changes. Again, I can't see that changing the angle is of any benefit.


    The last antenna is the 16" BT.





    For the 36-degree change, there was only improvement of greater than 1 dB but, again, they were small and only for three stations. The worst degradation was only -0.7 dB below the 1 dB threshold, so here one could say that the 36-degree angle is better to use than the 22-degree angle. On the other hand, since only one of those stations improved by more than 2 dB why bother?

    Looking at the 50 degree test, there were five stations that improved and four of those had better than 2 dB improvements. There were no stations better at 22 degrees by more than 1 dB, but channel 50 got close at 0.9 dB. In this area, none of the improvements were on stations that really needed improving. This was the only version of the bow tie that showed some improvement and not just a shift of better-to-worse channels.

    There were only improvements for the 16" bow tie when changing the angle to 50 degrees. All oher versions and angles simply made minor changes showing minor improvements for some stations and minor degradations for others.

    CONCLUSION:
    The conclusion is simply that the angle doesn't seem to affect the general frequency response of the antenna, no matter what the length of the bow tie element is. There were no noticeable shifts of improvements, most improvements were clearly scattered around, and some others are uncertain. The bottom line is that it didn't help substantially or consistently, so use a convenient separation and try to make all separations, in making the elements, the same as close as possible.

    The Bow Tie antenna has many different versions, from lengths of 5 to 9 inches that I have seen on the web and with angles from 22 to about 50 degrees. No length or angle that I have tested seems to make any substantial or consistent improvements including using or not using the standard transformer. So pick a length, a separation, and either use or not use the transformer, as you desire, and know that any change you would have made would probably not result in any substantial improvements. One thing I will point out is that you should use some form of RF blocking to keep RF off of the outer shield and since the transformer will do this as easily as buying a clip-on choke, and itís probably easier to find than a choke, it would be a good thing to use.

    Until next time, happy viewing!
    PhilK


    All my blog articles are listed at: Karras' Corner
    or
    Karras' Corner Article Links on my KE3FL web site.

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