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Discussion in 'CB Antennas' started by bestro, Feb 28, 2012.
Should work just fine . . .
Wouldn't hurt to put one on.
5 turns of RG-58 coax on a 4 inch PVC coil form below the feed point and not touching any metal of the mast should work OK.
An RF choke is not needed to prevent CMC, but as ROBB said it sure would not hurt anything.
If you live in a windy location the chimney mount may vibrate in the wind eventually cracking the mortar between the bricks on the chimney.
put it on chimmney mnt,it wont hold durring winds,it has a good wind load and ice load,73 de JW
roof antenna mount tripod - Google Search
You could look at something like this mount if you do not want to use the chimney.
i would not be drilling any holes into the chimney, if i'm seeing it right this sounds to be a small chimney to vent gases maybe from a gas furnace or other gas appliance but let us know if it is other wise.
i would check the integrity of the mortar and bricks well. I lived in an older house built in the 40's at one time and the mortar was falling apart after 45 odd years just from the elements alone.
My preference(if the integrity of the chimney is good) would be to use mounting hardware with stainless steel straps that wrap around the entire chimney.
Some folks say that standard antenna mounts are ok, but i like to be sure because there are considerable wind forces on the mast and antenna.
What would be worst case scenario, the chimney crumbles you may or may not be able to use said appliance, you hire a mason to rebuild you a chimney, then you buy a separate mast or tower. Just thinking outloud here, i like to think things through.
Hope this helps out and not hinders any. Best of luck
A gamma fed antenna won't create CMC?
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The transmission line (coax) shield is not part of the antenna or counter poise per say.
Common mode current
Some reading on CMC.
The Gamma match provides a transition from unbalanced coax to balanced antenna. Adjusting the Gamma for lowest Z or VSWR if only a VSWR meter is available will usually eliminate CMC as equal but opposite currents are flowing on the transmission line.
I have never seen a yagi excited with proper drive cause CMC, now I have seen amplifiers being over driven into saturation and beyond cause splatter but the yagi can not be blamed for the splatter, the operator sure can.
The bottom telescoping section was 10' and I had the next two extended 9' and 8' respectively, plus a 30" mast coming from the top of the HD-73 rotator. This was all on a 20' roof peak and guyed 4 directions so the boom was right at 50'.
Having no tower it was all I could do, and it lasted for over 10 years without issue before I took it down to try something different.
I didn't use a tripod at the bottom, I simply walked it up and set the bottom of the mast into the roof-mounting base (after setting the 12 well-insulated guy wires during a dry-run without an antenna on it) with the beam and rotator installed but collapsed down to about 15' total, then I leaned a ladder against the mast and pushed up the 2 top sections until the I saw the marks, then tightened the turnbuckles until taught & true.
It was a little hair-raising but it only took an hour or so afterword for my nuts to drop back down. :redface: