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Author Topic: Antenna question for my SW radio  (Read 371 times)
KC8YWO
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Posts: 19




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« on: February 16, 2007, 06:38:41 AM »

I currenty have an Icom IC-R75 SW receiver. I have it hooked to an RF Systems EMF wire antenna. Currently, part of the antenna is taped to the wall of my apartment with the remaining six feet dangling off my window blinds. The antenna is not mounted in a straight line, but rather thrown across objects.

First question: What is the difference between an active and passive antenna?

Second question: Should I consider an active antenna for my radio? If so, which brand/model?

Third question: Does it matter that my current wire antenna is not mounted in a straight line?

Fourth question: Any advantage in a loop antenna over a wire antenna?

For the most part, I am getting fair signals with my antenna, however a good SINPO rating quickly falls to a bad SINPO rating after listening for only a few minutes. I didn't know if it's due to my antenna mounting, type of antenna, or just the time of year for listening.

I enjoy listening to my SW receiver, but have become very disappointed in how fast the reception drops out.

Please be, "easy" on me. Although I am currently studying for my General certificate, antennas and propagation have been tough areas for me to grasp.

Any help would be greatly appreciated!

73's.

-Chris
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K7UNZ
Member

Posts: 691




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« Reply #1 on: February 16, 2007, 09:24:51 AM »

Hi Chris!

Nothing wrong with your questions, basically we all started asking the same ones ourselves.

Antennas are funny things, and what works well in one situation may be a total loss in another.  So I'll just keep it to a generalized response.  Bear in mind, you already have a very good radio!

Active (power required) antennas usually have a pre-amplifier and/or pre-selector.  That is, they are adjustable over a tunning range for "best" signal.  However, the better active antennas also rely on your being able to install the actual antenna outside, and in the clear.  Not always possible in apartment living.
Is it worth the money (a couple of hundred bucks for a good one), usually not for just listening.

A passive (no power required) antenna is simply an antenna directly connected to the radio, no external power required.  A hunk of wire, a dipole, a verticle, whatever.

Receiving antennas are quite forgiving and require no where near the care and tunning a transmitting antenna requires.  For apartment life, you can usually do just fine with a single wire running around the room on an exterior wall. As long as you can make it, and avoid running it near the power lines in the wall (great noise sources!).  Tack it up where the ceiling meets the wall, and go around the room if possible.  Longer is better.  Not sure about the R-75, but if it has a single wire antenna terminal, that's where you connect the end of this simple antenna.  If it only has a coax connector, then either just stick the wire in the center conductor hole, of add a bananna plug to the wire end for a better connection.  True plug and play...

Loops may, or may not, work better....depends on your specific location and installation.

The signal fade you mention is normal on HF.  It's a little worse now due to the solar cycle minimum, and also depends on frequency and time of day.  Don't expect much from the higher frequencies until the cycle improves. But expect the fade, even with a super antenna.  And in apartment living, expect noise!

Can't really say more without knowing more about your specific situation Chris.

Didn't mean to write a book.....hi!

73, Jim/k7unz





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AA4PB
Member

Posts: 12779




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« Reply #2 on: February 16, 2007, 05:05:02 PM »

Normally on HF with a decent receiver, an active antenna won't provide any benefit over a passive antenna. In order to get better receiption you have to increase the signal to noise ratio. On the HF bands the receiver is limited by the external noise that the antenna picks up. If you add an amplifier you amplify the signal and the noise by the same amount so the ratio and the receiption ability remains the same.
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