View Full Version : antenna choice
Mon 21st Sep 2009, 19:46
I've just got my foundation licence and i will shortly be putting up a decent antenna. I've got plenty of space on a flat roof about 30 feet by 120 feet but the problem is it's about 70 feet up and quite awkward to get up , so once its up i won't be able to get up and tweak it very often.
i'll be putting a small vertical for 2 meters but what would you guys suggest for hf?
i was thinking of a di-pole to cover 10 metres up to 80 or higher so what size would i need as a compromise to cover the lot ?
also would it be ok to hold it down with cable clips , the ones with the plastic bit to hold the cable and a small nail to go in the masonry? or does it need to be hanging freely?
thanks guys, john
Tue 22nd Sep 2009, 15:37
I would personally put up either a dual band Colinear( 2 meters & 70 Cm,) or a tri band Colinear that covers 6, 2 & 70. As that gives you options at a later date.
The dual band option will give you the best Db gain.
For the HF antenna you will be able to fit it to a wall or the guttering, but as an ex builder PLEASE don't fix it down to the flat roof, they are VERY prone to leaking.
If you have access to the whole surround of the flat roof I think I would probably go for a 180 meter windom & cable tie it to the guttering.
Wed 23rd Sep 2009, 11:50
Try to get the VHF antenna as high as possible, using the best coax you can afford - you'll find that you wished you had that extra foot (or metre) of height after a while :)
I had a flat roof once, fixing a longwire was no problem, I took a square of wood about 18 inches wide, screwed a wooden vertical about the same length, through the centre (so it looks like an uspide-down birdtable).
Put this about a metre or so away from the corner of the roof and put bricks on top (about 2 high).
Through the wooden vertical is a hole for a bit of plastic rope and an egg insulator.
A similar affair was at the low end of the roof, which led to a fishing rod, also with a bit of rope and an egg insulator, at the end of the garden.
Just an afterthought, make sure you secure the cables at the top when installing, they weigh quite a bit!
Wed 23rd Sep 2009, 17:19
using the best coax you can afford -
I'll second that...My first real operating lesson as an amateur was discovering I could hear stations on 70Cm using my handheld & whilst sitting in the garden that were not audiable on the base antenna with about 20 - 30 foot of RG-58 to the radio :oops: :oops:
My background was mainly on HF either operating Echo Charlie, Broadcasting on 48 etc or as a SWL & RG-58 when I started playing was the good stuff, as many were using TV coax on HF & VHF & UHF was a steep learning curve.
But lesson learnt...VHF & 70 Cm is now best quality RG-213 as a minimum.
There are lots of online loss calculators for coax & the difference between cheap 213 & good 213 can be more than a watt, even on a 20 meter run & with 10 watts out of the radio.
Wed 23rd Sep 2009, 17:49
I'll third that.
I use EcoFlex 15 for 2/70cm Collinear. It's not cheap, but I can run 10+ meters for same losses as less than 1 meter of RG-58.
Diode Communications in UK supply EcoFlex 15.
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