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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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Old 06-13-2018, 2:32 PM
   
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Smile help please.

im new to this forum, so please excuse my lack of knowledge,
i have been set a task from work to build an improvised antenna for a hf radio, using don 10 cable.
as i have been told the freq i have to use and cant be changed being 4.4650 mhz, we have to be able to transmit over 30m.

can anyone please give me some guidance/ help with how i can make a compact or smaller antenna that meets with these reqs.
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Old 06-14-2018, 7:00 PM
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A simple dipole would work if you have the room. The standard fomula for a dipole is 468/(frequency in Mhz) =(length in feet). Cut the above in the middle with an insulator and feed the two ends of the insulator with a coax to the radio. -Make sure you are licensed for that frequency. The range will vary based on time of day with daylight giving short range and nights the range will go out to hundreds of miles depending on power and electrical noise. That frequency behaves quite a bit like the AM broadcast band. The antenna should be as high as feasible and 'In the clear'. Use either a single wire or 'short' the two conductors together. Not sure how strong DO-10 but the antenna will be over 100 feet long so it may break under the strain.

More details about what you are doing would help a lot.
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Old 06-16-2018, 10:28 PM
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Hi Stan .....
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4465Khz... you aren't with the Russian Navy are you ...?...lol
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Don10 cable is a bit unique for antennas- its for military field 'phones, No?

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But is very strong, and it can support quite a heavy load.
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I am curious why you are using this frequency for a range that is so short-- 30 miles?... 4.5 Mhz can be a very long range frequency; day time 2-300 miles can be expected... at night time- the other side of the world. But if the distance gets too short, like your 30 miles , and there are intervening hills etc., the signals can drop down to noise. With normal antennas, it is just too close for any atmospheric returns, and too far for groundwave (which is practically non-existent on 4.5Mhz anyway.)
To have a successful close-in radio circuit on that frequency you'll need an antenna that radiates its energy nearly vertically- so the angle at which it is refracted comes done close to your station -- think geometrically. They are call'd Near Vertical Incidence (NVI) antennas, and most aren't difficult to construct.... the big thing if they are horizontal is to not elevate the wire more than 10-15 feet above the ground. You can construct a dipole (about 102 feet long @ 4.5Mhz,) or use a random length of wire with a tuner.
NVI is a major issue for close range HF tactical ground communications, and its important in airborne HF use. I could tell you stories about inadvertently switching in a NVI used for aircraft and wondering why we weren't talking any distance anymore. They can be very close range'd
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I hope this helps- but ask more question if necessary.
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Lauri
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Old 06-16-2018, 10:40 PM
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Curiosity got me and I did a quick search of DON10 wire for antennas .
Its not a usual antenna material, but it is wire, so 'why not?"
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At least this group thought so, and they discussed it from the advantage of their experiences-- perhaps adding at bit to all this ?
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https://www.eham.net/ehamforum/smf/i...?topic=64674.0
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Old Yesterday, 9:32 AM
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Default 4.465 MHZ

Like the Cobra Jr. antenna. Can be used as an inverted V.
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