Re: Useless questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
> 
> Interesting idea... especially since I have been looking at just such
> radars at work for another application.
> 
> One problem will be resolution, but that might not be a problem if you
> consider looking at the "bulk" characteristics of a volume of air
> containing some streamers. At 10 GHz, the wavelength is about 3 cm, and at
> 24 GHz (the other frequency for which these devices are readily available
> cheap), a bit more than a cm.  While one can get resolution smaller than a
> wavelength it's a pain.
> 
> The real problem will be that the inexpensive doppler radars (speed guns
> and the like) are hideously sensitive to interference.  They work by mixing
> a bit of the outbound signal (around 0.5 mW, typically) with whatever gets
> reflected back, and then looking at the audio frequency on the mixer diode.
>  This is called homodyne operation, by the way.   The problem is that the
> selectivity of the receiver is pretty bad; as in non-existent.  Any RF
> power that gets into the horn will be detected by the diode and its
> envelope will show up.

1. Homodyne receivers are plenty sensitive.

2. Think that the actual RF radiation from the streamers won't be a
factor.  Would be easy enough to check by just using the schottky diode
in the detector unit with the power removed from the transmitter.  I
think the main problem would be with audio pickup in the detector
output, and that could (probably) be minimized by careful shielding. 
I've taken pictures of streamers with my camcorder, and didn't have any
noticeable audio pickup when I stuck my hand in front of the mikes.


Ed.

I'm getting interested in the topic now, and wondering what I can do
with my little TC in the basement where the rest of the RF stuff is. 
Maybe...................