Help making a basic aerial

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Re: Help making a basic aerial

Postby m0lsx » Sat Jul 22, 2017 6:16 pm

Vertical. As a general rule, SSB is Horizontal & FM is Vertical.
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Re: Help making a basic aerial

Postby Portisheadsea » Sat Jul 22, 2017 7:33 pm

So, if I cut the legs at 47cm each then, and dont use an vswr , I'm not likely to damage the scanner am I if its not quite correct ?
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Re: Help making a basic aerial

Postby m0lsx » Sat Jul 22, 2017 8:03 pm

On receive you can experiment all you want & no, no damage will occur. It's transmit where you need to be careful.
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Re: Help making a basic aerial

Postby Portisheadsea » Tue Jul 25, 2017 12:50 pm

So, I've put this up in my loft. It definitely works. I'm collecting transmissions from all over the shop. I've used inner core of electrical cable and soldered to the coax core and shield.
Is it worth putting it outside on a wall?
Would it be worth using copper pipe? Does the thickness or the rods make any difference?

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Re: Help making a basic aerial

Postby m0lsx » Tue Jul 25, 2017 1:52 pm

That looks good. Putting it outside will improve reception. By 3 & 6dB is I thing the figure. So by around half to one S point.
But if you do put it outside don't use black or grey plastic tubing to shield it. As that often has graphite in it. Use white.
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Re: Help making a basic aerial

Postby uniden125 » Wed Aug 02, 2017 3:47 pm

Can you just cut back the sleeving of the coax to 47 cm and separate the two strands and open them in a straight line?

Secondly, what difference does the 75 Ohms make?

Third - is a balun needed and does it make a difference?

Newbie questions I know but we all start somewhere.
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Re: Help making a basic aerial

Postby m0lsx » Wed Aug 02, 2017 6:49 pm

uniden125 wrote:Can you just cut back the sleeving of the coax to 47 cm and separate the two strands and open them in a straight line?


Yes you could.
Take a look at designs like The Bazooka antenna & Coax antennas.

Image

http://www.iw5edi.com/ham-radio/?the-vertical-bazooka-antenna,18

Image


uniden125 wrote: Secondly, what difference does the 75 Ohms make?


In relation to SWR, very little. The SWR on 75ohms is 1.5:1 so on something like a quarter wave, which should have an impedance of 37ohms, it makes sense. The same with a few other antennas, 75 ohm Coax can make sense.
A half wave antenna should be 73 Ohms, so 75ohm Coax is no different to a half wave antenna when it comes to SWR.


uniden125 wrote: Third - is a balun needed and does it make a difference?


No, you will not, or not on a RX antenna.
And the word Balun is not a simple as it should be as we use it to describe things that are not actually Baluns.
A Balun should be something that matches balanced & unbalanced. It should transform. Hence 4:1, 9:1 etc. The numbers relate to the number of turns of wire.

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