Testing Ideas

Before doing any tests, these are my ideas for testing antennas:

All antennas are to be tested in the same way.

  • The antenna is placed at the same height
    • There are different kinds of gain antennas, so. . .
      • For a vertical (stacked) array, the center of the vertical height of the antenna is to be placed at the testing height
      • For a horizontal array, the center of the horizontal length will be placed at the correct height and centered on the antenna mast it is mounted to.
  • The antenna mast is placed in the same position (North/South/East/West).
  • The antenna must point in the same direction(s), at the same angle/heading.
    • Having some kind of pointing meter is probably a good idea so that the antennas can be pointed at the same tower and peaked so that we know, as best we can, that the antenna under test is now pointed as well as possible at the signal/channel, of interest.

I must admit that I have no way of figuring out the dBi or dBd gain of any antenna at present. My tools are simply not that good. My TV or DTV converter boxes give a number for the signal strength, but, there’s no documentation as to what that number means other than some kind of relative signal strength indication (similar to the old S-meter, I guess). Check your documentation and see if it says something similar to this: “a signal strength of 60 or above indicates a solid signal.” That’s not much to go on as far as I’m concerned but that’s all they give us.

I own an Alinco DJ-X10 wide band hand-held receiver which I can tune to any TV frequency. Originally, the frequencies placed into the receiver were for the audio FM section of the TV channel being monitored. Today it’s just a portion of the band being used in digital mode. I believe that I should be able to figure out some way to use the radio and its little band scope (spectrum display) to allow me to look at enough of the signal to see how good it is. The radio has its own attenuator built in which I can swap in or out, going through the menu system, and I also have 50 Ohm 3, 6, and 9 dB attenuators. The problem is that, with the limited display on the radio, it displays about one to eight vertical dots to indicate the signal strength for that frequency band. It might be impossible to determine the actual dB gain. I’ll probably just give relative improvement information from my standard reference antenna. If it seems possible to determine a measured improvement or loss, I’ll give that information in dBs.

Example: The signal strength measured using the TV’s meter reads 48 for the bowtie. The signal level for another antenna with a bit more gain reads 96. This is twice that of the bowtie, and if the meter is linear, we could say that the antenna has a 3dB gain over the bowtie or ~ 5 dBi. While dBi is 2.15 more than dBd, I’m going to drop the .15.

Again, I’m not certain that the TV meter is calibrated so that 100 is, in fact, twice 50. I would hope it is but it may not be. As far as I can tell from all the TV and converter box user guides, that kind of information is completely missing.

I fully expect that things will change. As I gain experience with the antennas and tools at my disposal, I fully expect that my testing skills will improve. I also expect to come up with better methods to determine the gain of any antenna under test.

Let me know your ideas on this as well. I know my new TV has a signal level meter and I’m fairly sure that all of my converter boxes also have meters. Unfortunately, I know that the little portable HDTV I have does not have a meter, or at least I’ve never been able to find it and there is no mention of it in any literature on the TV.

I have since tested a few things, the HDBLADE100 Blade antenna and the SL 1000 Signal Finder. I’ve also built a four element fullwave-loop turnstile antenna and am planning on testing out a friend’s location for TV signals. The DJ-X10 seems to do a good job at measuring a signal’s relative strength and with a little practice I should be able to figure out how to know from these signal levels if a signal is good enough to be able to watch. All of this will come out in future articles.

Until Next Time,
Phil Karras