so im wondering if its possible to build an antenna that would cover 70CM-6M? and id like it if it was a multi load single unit, but not even sure if its possible. any ideas? and i understand that 2M and above would obviously have to be quarter-wave or less.
multi band antenna
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majoco
Stirrer
Why build when discones are freely available, 6m = 50MHz, 70cm = 430MHz approx, not a great ask. I wouldn't transmit on all those frequencies but receive only shouldn't be a problem.
I created an account on this forum just so I could ask you this: Where do you find freely available discones?
N3JI
Member
Since you didn't specify omni or directional, and RX only or TX/RX, a TV antenna with VHF-Lo will cover that range, which will be directional, likely an LPDA. Tennadyne makes an LPDA also that covers that range and then some for both RX and TX. I personally have a vertical that covers 6m/2m/70cm, but not continuously for TX. RX it works well though. It's a Diamond V2000. Diamond® Antenna ~ V2000A Tri-band Base Antenna
And a Discone was already mentioned for continuous omni coverage...
Good luck,
Joe
Are you looking for a free discone, or are you looking for a place to buy one from?
Diamond makes some pretty good antennas.. Here' a link to one of their products. Diamond® Antenna ~ D3000N Super Discone Antenna There's a link on that page to help you locate a convenient dealer.
A tradational, properly designed Discone covers a frequency range of about 8:1, so if you have a big one that goes down to 6m or 50MHz, its top end would be around 400MHz. Another problem is the Discone radiation pattern is good at the horizon from its lower design freq to about halfway through is range then the pattern shifts upward and the performance at the horizon is diminished, so a 50Mhz Discone would be usable to about 200Mhz then the pattern shifts up.
Otherwise, its very difficult to design an antenna that will cover 6m through 70cm or 50MHz through about 450MHz. A nest of dipoles or a ground plane with multiple elements is a problem due to lower freq elements operating as a 3/4 wave on higher bands with a not so good radiation pattern at the horizon and if you add 1/4 wave resonant elements where another resonates as a 3/4 wave, they both will carry current on the band of interest with undesirable patterns and they will load down the feedpoint impedance too much.
Plus a nest of dipoles or multi element ground plane will only work well on the few discreet frequencies its designed for and not continuously from 50 to 450MHz and so on. If you want all those bands then there are commercial antennas already designed for those bands, or for continuous coverage you could use two Discones that cover different parts of the bands and combine them with a diplexer.
prcguy
Otherwise, its very difficult to design an antenna that will cover 6m through 70cm or 50MHz through about 450MHz. A nest of dipoles or a ground plane with multiple elements is a problem due to lower freq elements operating as a 3/4 wave on higher bands with a not so good radiation pattern at the horizon and if you add 1/4 wave resonant elements where another resonates as a 3/4 wave, they both will carry current on the band of interest with undesirable patterns and they will load down the feedpoint impedance too much.
Plus a nest of dipoles or multi element ground plane will only work well on the few discreet frequencies its designed for and not continuously from 50 to 450MHz and so on. If you want all those bands then there are commercial antennas already designed for those bands, or for continuous coverage you could use two Discones that cover different parts of the bands and combine them with a diplexer.
prcguy
N3JI
Member
ANY multiband antenna is going to have pattern shifts from one frequency band to the next, with very few exceptions. How it's mounted, proximity to other structures and antennas, how the feedline is routed, and height will all cause differences. But either way, we still don't know exactly what he wants to build (I actually missed the part about him wanting to build it), so I think we still need more info. The RS discone I use has a gap between 50 & 100 MHz because of the "stinger" it uses for 50 MHz coverage, but is quite good up to 70cm.
Free as in beer or very inexpensive. I read majoco's comment to mean that there are businesses and people practically giving them away -- maybe government surplus or whatever.
But if majoco meant "freely available" as in "widely available" then yep I found Diamond antennas and such.
majoco
Stirrer
Well, mine was 'free' as I retrieved it from a scrap heap but I really meant "widely"! Sorry for the confusion 
Well, mine was 'free' as I retrieved it from a scrap heap but I really meant "widely"! Sorry for the confusion
Free as in speech. Ok no worries!
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