My reply was there are two answers, the "correct and academic" one and the "I don't have a 25m tower" answer. The former is covered in great detail on g3sek's excellent ifwtech.co.uk website and other places I'll mention later and the latter is "as far away as is practical to put it given your space!"
Now unlike many active stations on VHF and up, here on the Fen Edge I live in a modest house, surrounded by neighbours, so a tower is a non starter and all my Terrestrial antennas live on two poles, one on each gable end. I manage 2 VHF bands, and at least 3 microwave bands with this system, but compromises have to be made. A single 60cm dish does two GHz bands without compromise (except maybe height agl) but the boom of my 1296MHz Yagi is only about 500mm above the boom of my 50 and 70 MHz YU7EF dual bander. They both "work," the VSWRs are not compromised and I get excellent results on 1296 and can have Sporadic E fun in the Summer on the lower bands. That's really all this hobby is about to a certain extent.
My Good friend Kent Britain WA5VJB (Google his name and you'll see he's a "proper" antenna engineer as well as being a bit of an iconoclast) authored an excellent paper in the 2010 Central States VHF conference proceedings about
close stacking and is a "must read" on the topic. In it he states that UHF antennas can be stacked "closer than you think." Unfortunately that paper does not seem to be on-line anywhere obvious, but it was covered in Winter 2010 "CQ VHF." Gerald Johnson K0CQ's follow up paper takes the usual "Dr Jerry academic approach" and is worth a read.
I've
always put my antennas as far apart as I can here, and with me that's
very close indeed as I only have a short pole on the gable end. I have
serious limitations when winching the pole up past
the house eaves.
Honestly, I wouldn't die in a ditch about it, and take
the pragmatic view for terrestrial that as long as the VSWR is not
seriously compromised by proximity just do it!
Or don't sweat about what
you can't control! Live with it!
1 comment:
John, Thanks for the post and notes (it was me!).
72 Dom M1KTA
Mentioning gable end antenna mounting.
Got to laugh... neighbor, who rents his house put up a TV pole with not one but three separate Digital TV antennas on it...didn't ask permission either it seems. He took the H&K bracket off the main house wall (I have no idea how!) where it was fine, moved it to the gable end of the old downstairs toilet. Every house on street uses the house wall but he knew better obviously and that also meant he could do it with a low ladder.
Up come the high winds... he discovered why everyone was telling him it is a bad idea to put it there, it is lime mortar single skin brick so it will not hold a loaded 20ft pole in high winds in a million years.
Rats was too slow with the camera (I was laughing too hard) has covered the collapsed wall and caved in roof with a sheet.
I guess that is his security deposit gone then!
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