This update includes MOVING the Feedline point (the 300-75ohm transformer) to see
what affect it has on the Searcher II antenna.
*photo at the right - far right is NORMAL Position, Center is Yes... CENTER Postion, and far left is END position, you will need this information when viewing the charts if you are unfamiliar with this antenna.
I charted the normal setting for the Antenna, by normal I mean where the original ST-2 antenna placed the transformer which is out on the end with the small radials which are used in the 800-1000MHz range.
I then moved the Feedline transformer to the CENTER of the antenna mounted to the Long center radials. and I recorded those numbers as well.
I then moved the Feedline transformer to the very end of the antenna where there are NO radials the the aluminum connecting rods that go from point to point and tie the antenna together, I think I may have called them Transmission lines at one point, I am sure you know what I am talking about.
I calibrated the VNA at the beginning of this test, when I moved the transformer feedline to the other sections I DID NOT RE CALIBRATE the VNA, I wanted the same calibration to read all the feed point changes, every time you re calibrate the VNA, it puts new setting into the way it reads the antenna, I wanted all the positions measured with the same VNA setting so I DiD NOT re calibrate when moving the transformer from position to position. Is this the right way to do testing? It is when I am doing it, You can do it however you want :).
Scans in all 3 positions were run from 25.000MHz to 1000.000MHz and Peaks and Valleys were recorded.
There were 125 points measured and documented for each of the three positions
for a total of 375 points, this took about 2 1/2 day's to combine into a chart.
...............( to be continued)..............
I wasn't really sure what this testing would show but I knew it had to make changes to the antenna.
The testing showed that when the transformer (feedline point) was in the Normal position it had a clear advantage from 25MHz - 334MHz.
When the feedline (transfomer) was moved to the Center position there was NO Major change, Yes it caused change no doubt about that, but it made no specific change as far as any certain band width improvement.
With the feedline (transformer) was move to the END position, there was a considerable change for the better from 336MHz-586MHz.
The rest of the bands from 593MHz - 1000Mhz data showed no noticeable favor to any of the 3 positions, mostly hit and miss for all the positions see below.
593MHZ - 635MHz - Slight advantage in the End Position
642MHZ - 708MHz - Slight advantage in the Center Position
717MHz - 783MHz - No noticeable change from any of the positions
719MHz - 857MHz - Slight advantage in the Center Position
865MHz - 922MHz - Slight advantage in the Center Position
931MHz - 1000MHz - No noticeable change from any of the positions
When I refer to the changes, That is in reference to the NORMAL position
of the Transformer, which is where 99.9% of ST-2 users would put the
Transformer since that's where the Antennacraft manufacture tells you to put it.
This is NOT a ST-2 antenna, But Testing is compared to Normal ST-2 use.
If you were to move the transformer on the ST-2 (which you can't because they use rivets in the center and end positions) you would see and get the same results as my testing show's or very very close to it
From a testing stand point, I would say with the Transformer feedline placed in the Normal position you would see the standard results of any ST-2 antenna, However if your range of monitoring is in the 330-600MHz range I would move the transformer to the End Position.
Charts from this testing is shown below.
I did Feedline testing by removing the connecting rods between the elements.
Those results were very interesting.
The test VNA photo's above are not very good in quality, but I feel they are good enough to get the idea of what's changing when modifications are carried out.
Details of the modifications will not be revealed.