How close can I install the OCF DX Flagpole to my home?
Hello Friends and Peers!
Many have asked, "how close can I install the antenna to trees" or "my home" and "surrounding buildings" so we asked antenna designer and engineer, John Portune.
He came back with a worst-case scenario for us by calculating an OCF Flagpole near metal siding!
John's findings are encouraging indeed. What can you learn from John's experiment? Read his notes below and let us know your thoughts too!
TU and 73
Does it matter where you mount the pole?
By John Portune (October 29, 2018)
My existing 20 ft. flagpole (4+16 ft. 2 in. aluminum, 1 ft. fiberglass base insulator and 4 in. fiberglass feed point insulator spacing) sits roughly 18 in. from my metal-skinned mobile home. I added a new mount 15 ft. away from the house.
In both locations I used my VNA to measure the impedances and SWR's at the input of the 5 ft. 450 Ohm ladder line from the base to the feedpoint in three situations.
(1) near the house with a flag,
(2) away from the house with flag and
(3) away from the house without a flag.
The graph below shows the SWR vs. frequency.
Clearly, the flag has no effect, the two curves, with and without a flag, totally overlap. From 40m and up, the house has only a little effect. On 80m the house increases the SWR.
I also measured the impedances but did not plot them on this chart. The R is very much the same for all bands. The reactance (X) follows the SWR. These are not surprising.
I think these measurements show that the user does not need to pay much attention to where he mounts the pole. My metal-skin house is pretty much a worst-case scenario. However, very close to a large metal building may make it difficult for an auto-tuner to tune on 80m.
Thanks, John! Hope you learned a little something here. I sure did. Looking for just a little more confidence to get you and your friends back on the air!
73 Jon KL2A