From: Crusty Curmudgeon
Subject: Re: Simple? RF question
X-Newsreader: Forte Agent 1.9/32.560
Date: Fri, 03 Jan 2003 22:57:12 -0600
NNTP-Posting-Date: Fri, 03 Jan 2003 22:56:06 CST
Go ahead and ground the circuit to the box. It'll be more stable. However, if
your transmitter is a simple single stage LC oscillator with an antenna
attached, any movement of or contact with the antenna will likely shift the
frequency. It takes several stages of isolation/amplification between antenna
and oscillator to reduce this effect. If you're using a quartz crystal
oscillator the effect is much less, but still measurable.
Mobile 'whip' antennas are notorious for 'singing' in the wind causing FM
modulation of transmitters. I suppose with calibration, you could take advanage
of this to gauge wind speed. :)
On Fri, 3 Jan 2003 21:51:43 -0500, "numberdude" wrote:
>I've been experimenting with FM beacon transmitter circuits as a learning
>project for myself. So far, I've only breadboarded the latest circuit and I
>want to build it permanently. I plan to use a small RF shielded steel box
>from Sescom. I've heard they're pretty good for RF shielding. My question is
>this: I've noticed that some of these circuits get thrown off frequency if
>you touch the breadboard, I guess from body capacitance. Will the RF
>shielded box prevent this? Will it make a difference if I ground the circuit
>to the box? Is there anything else I should consider to reduce this effect?
>Thanks as always for sharing your knowldege.