Low-band dipole (DB212) mounting question

[n4dbm]

Hi,
I have had quite a bit of experience with the DB-212 low-band antenna elements, from one, two, and four element arrays mounted directly to the tower face. I have converted quite a few to the 6-meter ham band with a perfect match at 52.5 MHz when mounted directly to the tower.

I have an opportunity to have an old "emergency management" 47 MHz dipole removed, then replaced with my 52 MHz element, but it has to go on the tower EXACTLY as the old one came off. I have added a photo for clarity. The existing element is mounted to a "perch" which is about a foot away from the tower. The DB212 instructions say to mount the element directly to the tower for proper tuning and loading. While the existing 47 MHz antenna matches well at the end of the feed-line in its current state, I am curious to hear opinions on how this might affect the pattern and how unpredictable it may be. The element is at 850 feet and fed with 950 feet of 7/8" Heliax.

Perhaps with the amount of metal behind the antenna, the extra foot off the leg won't make much difference. The tower face is 6 feet and the legs are 4 inches in diameter.
Thanks for the opinions.

 

[prcguy]

Your antenna will be a little shorter getting it a little further away from the sheet metal above and below the antenna, which I think is a problem. The current antenna is much further away from a reflector compared to factory specs, so I believe the pattern will be narrower and the impedance will be a little higher and your higher freq antenna would be slightly worse.

 

[n4dbm]

I'm trying to understand what "slightly worse" means.. Worse gain, worse VSWR, worse overall pattern? Unlike the Sinclair and Comprod loops, which have instructions to vary the distance off the tower in respect to frequency, the DB212 dipoles, from 25-88 MHz all use the same spacing from the tower. Such a small amount of spacing is what Decibel Products claimed made their DB212's more omni-directional even when mounted on one side of the tower. The match where it's cut for is near perfect on the ground, given 2.2 dB of feed line loss.. So the match is very good even though the antenna is mounted a foot out from the tower further than what it's supposed to be.. Seems odd, as I would have thought doing such would have really made the match pretty bad.

The ice shield above it is something else that I'm not fond of, either. I can't help but think it's affecting it somehow, because there isn't supposed to be anything 1/4 wave above or below the low-band antenna to begin with.

Don't know what the end results will be. Whatever the result is, it will have to be better than what it is now for 6-meters. The people who used this 47 MHz system 20 years ago said they could work this station in most all directions 60+ miles out in the mobile with a 50 watt Desk-Trac station at the base. Guess we'll find out when and if we are able to get it changed.