Simple Base antenna
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Simple Base antenna
Looking to put an antenna for a 45w GM300 in place in an attic. I cant afford to install an exterior antenna. If i use a standard 1/4 wave antenna mounted to a metal plate, will that suffice to do the job? The primary mission of the radio is receive, as opposed to transmit. It will rarely be used to transmit.
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Tom in D.C.
- Posts: 3859
- Joined: Tue Sep 04, 2001 4:00 pm
- What radios do you own?: Progreso soup can with CRT
Re: Simple Base antenna
What you describe should work fine. If you want to pick
nits, use wire radials rather than a plate. That way you can
bend the radials down somewhat and get a real 50-ohm
match. If you use a plate make it a half wave in diameter,
meaning a quarter-wave radius.
nits, use wire radials rather than a plate. That way you can
bend the radials down somewhat and get a real 50-ohm
match. If you use a plate make it a half wave in diameter,
meaning a quarter-wave radius.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: Simple Base antenna
Can you explain that in beginner terms! Dimensionally please. Thanks. The antenna is the 18" whip that, as I understand is referred to 1/4 wave. I have an old steel mounting plate for a syntor radio that I can mount it to, will that work?
Re: Simple Base antenna
Antenna lengths and radials can be figure out in a simple formula:
L=234 divided by frequency in MHz for 1/4 waves
L=468 divided by frequency in MHz for 1/2 waves (the totals you receiver are antenna lengths in feet)
Example: say you want to create a 1/4 wave antenna for 150MHz
234 divided by 150 = 1.56 ft. or a 17.6 inch antenna. If you wanted to mount it to some sort of steel plate it would be mounted in the center of roughly a 35.2 inch plate but as Tom pointed out that will not be a true 50 ohm impedance but will probably be close enough for what your looking to do.
Doug
L=234 divided by frequency in MHz for 1/4 waves
L=468 divided by frequency in MHz for 1/2 waves (the totals you receiver are antenna lengths in feet)
Example: say you want to create a 1/4 wave antenna for 150MHz
234 divided by 150 = 1.56 ft. or a 17.6 inch antenna. If you wanted to mount it to some sort of steel plate it would be mounted in the center of roughly a 35.2 inch plate but as Tom pointed out that will not be a true 50 ohm impedance but will probably be close enough for what your looking to do.
Doug
May the Schwarz be with you.
Re: Simple Base antenna
So, if I understand, the antenna has to be mounted to a metal surface, I already figured that. Does that surface have to be grounded?
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Tom in D.C.
- Posts: 3859
- Joined: Tue Sep 04, 2001 4:00 pm
- What radios do you own?: Progreso soup can with CRT
Re: Simple Base antenna
Not really. It will be automatically grounded to the shield of
the coaxial cable you run from the radio to the antenna connector,
or if for some reason it's not then it should be. An actual earth
ground, like in old time radio days, wouldn't be necessary with an
antenna such as this. If you got into something more permanent,
and the antenna was outside on your roof, that would require proper
grounding of the system.
The way the vertical antenna works is that the quarter-wave that sticks up does most of the radiating of power, and the plate, or ground plane, takes the place of the other half of the antenna, making it a kind of skewed half-wave antenna. The vertical part connects to the center of the cable and the ground plane/plate is connected to the shield braid of the antenna. With a setup like this you should have no problems getting it to work very well immediately with no problems. Just be sure to cut the vertical
piece as exactly as you can to the middle frequency of all the
channels you'll be transmitting on.
the coaxial cable you run from the radio to the antenna connector,
or if for some reason it's not then it should be. An actual earth
ground, like in old time radio days, wouldn't be necessary with an
antenna such as this. If you got into something more permanent,
and the antenna was outside on your roof, that would require proper
grounding of the system.
The way the vertical antenna works is that the quarter-wave that sticks up does most of the radiating of power, and the plate, or ground plane, takes the place of the other half of the antenna, making it a kind of skewed half-wave antenna. The vertical part connects to the center of the cable and the ground plane/plate is connected to the shield braid of the antenna. With a setup like this you should have no problems getting it to work very well immediately with no problems. Just be sure to cut the vertical
piece as exactly as you can to the middle frequency of all the
channels you'll be transmitting on.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
Re: Simple Base antenna
Thank you