Help making a basic aerial

A place to talk about everything Radio and Scanning

Help making a basic aerial

Postby Portisheadsea » Fri Jul 21, 2017 10:30 pm

Hi.
Id like to make and put a basic aerial on my roof to scan marine channels as the attached aerial on the scanner isn't much good down stairs .
I have a TV Wall socket that I'm going to modify which has coax up to the roof and as I live next to the Bristol channel Id like to use a better aerial. Could anyone tell me how to make a basic aerial I can attach to coax and put up there?
Portisheadsea
 
Posts: 6
Joined: Fri Jul 21, 2017 3:25 pm

Re: Help making a basic aerial

Postby m0lsx » Fri Jul 21, 2017 11:12 pm

If you are using the TV coax, don't forget it's 75 Ohms. That is not an issue, just something to take into account when you are making the antenna.
A radio wave travels at 300,000 meters per second. So 300 divided by the Megahertz, ( MHz,) gives you a starting point for a free space length.
I assume the main frequency you want is 156 mhz spectrum. So cut it for about 156.500 which gives 1.91 meters. This will be too long. as it's a free space wavelength. A half wave is thus 0.95 Meters & a half wave centre fed is a decent antenna, so thats 0.47, or 470cm per leg, before you slowly fold a cm at a time back & then cut, until you get the right VSWR.
Always fold the wire back on it's self, check the SWR & then cut.
A simple chocolate block will give a connection between coax & antenna.
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
73 De Alan (M0LSX.)
http://www.qrz.com/db/M0LSX"
User avatar
m0lsx
 
Posts: 5146
Joined: Wed Nov 21, 2012 9:14 pm
Location: Norwich. TG21.

Re: Help making a basic aerial

Postby deadite66 » Sat Jul 22, 2017 7:49 am

i made a chocblock dipole for marine band, though it's in the attic and not the roof.
http://imgur.com/a/xkV3q

connected to a rtlsdr v3 dongle, would dearly love to put my airspy on it but the program i'm using is rtlsdr only atm.
Airspy R2 on a Discone
rtlsdr v3 on a choc bloc copper dipole.
Windows 10 and Antergos Linux.
Yupiteru MVT-9000 MKII telescopic ant.
RSP2 Pro currently unused.
deadite66
 
Posts: 15
Joined: Sun Dec 20, 2015 6:38 pm
Location: Great Yarmouth

Re: Help making a basic aerial

Postby Portisheadsea » Sat Jul 22, 2017 10:18 am

Are you saying I need 4.7 meters per leg on an antenna?
I was hoping for something like about 1mtr long or so??? I don't have that much room! Must be a typo?

Or am i missing something
Also I don't have an swr Meter. Is it that crucial?
I'm looking at listening to stuff around 30 miles line of site I guess

Also, I can't really see from deadite66 picture, does one leg get soldered to the core of my coax and one leg to the shield?
General electrical core wire ok for the legs?
Portisheadsea
 
Posts: 6
Joined: Fri Jul 21, 2017 3:25 pm

Re: Help making a basic aerial

Postby alpha_india » Sat Jul 22, 2017 11:16 am

Portisheadsea wrote:Are you saying I need 4.7 meters per leg on an antenna?
I was hoping for something like about 1mtr long or so??? I don't have that much room! Must be a typo?

Or am i missing something
Also I don't have an swr Meter. Is it that crucial?
I'm looking at listening to stuff around 30 miles line of site I guess

Also, I can't really see from deadite66 picture, does one leg get soldered to the core of my coax and one leg to the shield?
General electrical core wire ok for the legs?

No, he meant 47cm and an extra zero crept in.

If you search the forum you'll find details of a choc block bowtie (search for "bowtie") which is a really effective antenna that costs next to nothing to make and covers a good range of frequencies. I use one in the loft and it's good for airband and marineband.
alpha_india
 
Posts: 212
Joined: Thu Mar 19, 2015 10:56 am

Re: Help making a basic aerial

Postby deadite66 » Sat Jul 22, 2017 11:33 am

sorry it wasn't clear.
new pic http://imgur.com/a/u2Mve
ignore the red wire i only added it for stability.
Airspy R2 on a Discone
rtlsdr v3 on a choc bloc copper dipole.
Windows 10 and Antergos Linux.
Yupiteru MVT-9000 MKII telescopic ant.
RSP2 Pro currently unused.
deadite66
 
Posts: 15
Joined: Sun Dec 20, 2015 6:38 pm
Location: Great Yarmouth

Re: Help making a basic aerial

Postby m0lsx » Sat Jul 22, 2017 11:37 am

Sorry about that zero..

The Bow tie makes perfect sense for a RX only antenna. They do also make good TX antennas. But the fact they are wonderfully broadband, means length is not critical..
The following site will allow you to design a antenna from a centre frequency.
http://www.changpuak.ch/electronics/Butterfly-Antenna-Designer.php
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
73 De Alan (M0LSX.)
http://www.qrz.com/db/M0LSX"
User avatar
m0lsx
 
Posts: 5146
Joined: Wed Nov 21, 2012 9:14 pm
Location: Norwich. TG21.

Re: Help making a basic aerial

Postby Portisheadsea » Sat Jul 22, 2017 12:37 pm

Thanks guys. Perfect picture dead.

Great helpful info.
I'll give it a try and come back with results?!
Just need to find some wire now! Wooden coat hangers are no use...
Portisheadsea
 
Posts: 6
Joined: Fri Jul 21, 2017 3:25 pm

Re: Help making a basic aerial

Postby m0lsx » Sat Jul 22, 2017 1:26 pm

Portisheadsea wrote: Just need to find some wire now! Wooden coat hangers are no use...


Have you discovered Freegle & Freecycle? They are recycling sites where people can pass on unwanted items. I have acquired some very usable bits & pieces via them down the years. The rule is, it must be free.
I have also passed on some of my unwanted bits & pieces to some really nice people too. The idea is what you call rubbish, someone else will say it's just what they want.
I also find that the brake cables from Police Cars make good antennas too :biggrin: :biggrin:
And just to avoid any misunderstanding. The above was not a serious comment. They make a better mast support than an antenna. :thumbup: :thumbup:
Buy a database from Kimmy JS19 via http://ukscanningdirectory.co.uk/
Or do Google search of this forum via https://www.google.com/cse/home?cx=partner-pub-6291336405621919:2662881632
73 De Alan (M0LSX.)
http://www.qrz.com/db/M0LSX"
User avatar
m0lsx
 
Posts: 5146
Joined: Wed Nov 21, 2012 9:14 pm
Location: Norwich. TG21.

Re: Help making a basic aerial

Postby Portisheadsea » Sat Jul 22, 2017 5:39 pm

Does it go horizontally or vertically?
Portisheadsea
 
Posts: 6
Joined: Fri Jul 21, 2017 3:25 pm

Next

Return to Radio and Scanning Chat

Who is online

Users browsing this forum: Silage, Yandex [Bot] and 4 guests