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I'm pretty new to all of this, so if this is a silly question forgive
me ![]() I thought I'd go ahead and make a 2m Yagi antenna so I can give transmitter hunting a try. (The plan I'm using is made of PVC pipe and 1" tape measures ... simple enough.) The other thing you usually need is an attenuator, to cut the power when you get close. I've got instructions for one of these too, and it's pretty simple -- just a bunch of resistors and double throw switches to activate each stage, all in a shielded box. The values of the resistor are given without explanation, but I'm sure those values were chosen to 1) attenuate the signal by the desired amount and 2) maintain the antenna/radio's impedance of 50 ohms. (I guess I could verify this with a little math if I felt the need ...) With about 5 stages, the total cost of parts is $30-$40 at Radio Shack. Since you're not going to be transmitting through this attenuator anyways (it would just release the magic smoke) then why is it important to keep a good SWR ratio? Couldn't you just take a variable resistor (with an audio/logarithmic taper) and put it in series or parallel (which exactly depends on it's value) with the antenna input, and then adjust as needed until you have a sutiable signal level again? Or would the messed up SWR ratios actually make the antenna not directional anymore or something like that? (http://members.aol.com/homingin/index.html has lots of stuff on transmitter hunting, but no answers to this question. The offset attenuator seems good, however ![]() -- Doug McLaren, "Can of worms? The can is open... the worms are everywhere." |
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