KB2GOM
Active Member
Someone here on RR posted that they had repurposed an old TV rabbit ears antenna for monitoring air frequencies and that it worked pretty well (If I could find the post again, I would reference it). If I recall correctly, they adjusted the rabbit ears until each was about 18 inches long. I look up online, and a quarter-wave of 128 MHz is around 19 inches. Close enough.
Hmm, I thought, I've got an old rabbit ears antenna somewhere . . . I found it; a ham friend (thanks, Steve!) whipped up a jumper cable to connect the rabbit ears to the BNC connector on my SDS200, and -- voila! -- we're in business. I figure the ATIS signal at Albany Country Airport will work just fine as a reference signal, so I lock the SDS200 onto that. The indoor antenna I am using for the SDS200 is a Comet W100RX, extended to its full length, about 40 inches. The signal strength meter is showing just one bar.
I hook up the rabbit ears (set to 18 inches long) to the SDS200, and the ATIS signal is immediately worse; no bars. Making sure the switch on the antenna is set to VHF, I try clicking the dial for various VHF settings on the rabbit ears antenna. No improvement, and some positions are noticeably worse.
As I am putting the Comet antenna back on the SDS200, I notice that there are markings on the black barrel of the first segment of the telescopic antenna. One of them says "VAIR," and it indicates that the W100RX should be extended 5 1/2 segments to receive VHF air frequencies. So I try that and -- ta da! -- the SDS200 shows two bars on the ATIS signal. Cool! I measure the length of the Comet antenna at 5 1/2 segments, and it's 27 inches to the right-angle bend where the BNC is connected.
So maybe the rabbit ears need to be adjusted to 27 inches. I try that, and it works no better than before.
That 27 inches looks kinda familiar, though, so I measure the stock telescopic antenna that comes with the SDS200, and it is almost exactly 27 inches. I connect that antenna to my Uniden 125AT, and it, too, shows two bars of signal strength on the ATIS frequency (and that's better than my Diamond 77 antenna). Very nice . . . an improved setup for listening to civilian air frequencies on two scanners.
But now here is the question: why should a 27-inch antenna work better? It's not -- as near as I can tell -- quarter wave, or half wave or five eighths wave. It is approximately 3/8 wave.
Can someone please shed some light?
Hmm, I thought, I've got an old rabbit ears antenna somewhere . . . I found it; a ham friend (thanks, Steve!) whipped up a jumper cable to connect the rabbit ears to the BNC connector on my SDS200, and -- voila! -- we're in business. I figure the ATIS signal at Albany Country Airport will work just fine as a reference signal, so I lock the SDS200 onto that. The indoor antenna I am using for the SDS200 is a Comet W100RX, extended to its full length, about 40 inches. The signal strength meter is showing just one bar.
I hook up the rabbit ears (set to 18 inches long) to the SDS200, and the ATIS signal is immediately worse; no bars. Making sure the switch on the antenna is set to VHF, I try clicking the dial for various VHF settings on the rabbit ears antenna. No improvement, and some positions are noticeably worse.
As I am putting the Comet antenna back on the SDS200, I notice that there are markings on the black barrel of the first segment of the telescopic antenna. One of them says "VAIR," and it indicates that the W100RX should be extended 5 1/2 segments to receive VHF air frequencies. So I try that and -- ta da! -- the SDS200 shows two bars on the ATIS signal. Cool! I measure the length of the Comet antenna at 5 1/2 segments, and it's 27 inches to the right-angle bend where the BNC is connected.
So maybe the rabbit ears need to be adjusted to 27 inches. I try that, and it works no better than before.
That 27 inches looks kinda familiar, though, so I measure the stock telescopic antenna that comes with the SDS200, and it is almost exactly 27 inches. I connect that antenna to my Uniden 125AT, and it, too, shows two bars of signal strength on the ATIS frequency (and that's better than my Diamond 77 antenna). Very nice . . . an improved setup for listening to civilian air frequencies on two scanners.
But now here is the question: why should a 27-inch antenna work better? It's not -- as near as I can tell -- quarter wave, or half wave or five eighths wave. It is approximately 3/8 wave.
Can someone please shed some light?