Re: interesting discovery closeness of scanner antenna ok try again


Message posted by lone wolf on June 08, 2004 at 13:15:21 PST:

It's not that I didn't see the original post, it's that I don't have a good answer for the question. I looked up the part number and figure the antenna would be a half wave a bit above 200Mhz. From the diagram in the catalog, it appears to have radials on the bottom, which act like a ground plane. My guess is that when you had it on the ground, you may have been getting a lucky reflection.

Scanning aircraft is a funny task. Generally what you do with a vertical antenna to get gain is you stack antennas with phasing element between the stack. This is known as a colinear design. Sometimes the phasing element is just the antenna coiled up a bit, and sometimes the element is "covered" in a metal container, that is you see a bulge on the antenna. However, stacking antennas makes the response to the sky get weaker and concentrates the radio signal out on the horizon. Imagine that the antenna reception pattern went from a ball to a donut. The taller the antenna, the flatter the donut. With a vertical antenna, there is no reception at all from directly above it.

What you see used most often for aircraft reception by the military is a small discone:
http://www.rami.com/mil028.htm
The discone is wideband, has some reception to the sky, but is low gain. This particular discone is designed just for mil air. The ones radio shack and diamond sells really aren't all that good because they don't have enough radials. This antenna is hard to find used, and you wouldn't like the price of a new one. They are about $100 on the used market, and require a bit of hacking to convert from a military connector, HN, to a standard N connector.

What I do for military air is use this:
http://www.rami.com/mil015.htm
mounted to a piazza pan for a ground plane. It's low gain, but also has reception towards the sky. This antenna shows up on ebay motors in the avionics section from time to time. I got one for $25 plus shipping. The antenna has a female N connector. I modified a magmount to hold a male N connector.


In Reply to: Re: interesting discovery closeness of scanner antenna ok try again posted by aaron johnson on June 08, 2004 at 11:46:36 PST:

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