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RE: FMCW radar question...



Art is right,
A few points: 
- A triangular Freq modulation is good, a sawtooth might be better. (because
targets appear only on one side of carrier)
- You need to modulate both the TX and RX (LO) (So targets are resolved to a
single frequnecy). (To see how this works, plot Ftx - (Ftx + delay).. for a
sawtooth, this is a fixed freq proportional to delay (except at transition
points))
- Typically, the resolution you ideally get is proportional to
3e8/bandwidth, IE for a  
10MHz sweep, dont expect better that 30M.
- Faster sweep might help separate target from carrier, at close ranges
- Dont forget to use radar equation to estimate the received target power...
Knowing how much power you are trying to see will help evaluate if the
signal is actually sitting in the phase noise area of LO.
- Typically, these systems require very accurate waveforms to get close to
the theoretical output. Distortion is a big killer. (Digital baseband
generators are the norm these days).

You havent mentioned if you are using CW or Pulsed CW (are you TXing while
trying to listen?). How good is your modulation & Phase noise?
Im happy to help more offline.

Sounds exciting! Good luck 
Dave M.
VK5DSM.


-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
Behalf Of KC6UQH
Sent: Saturday, 23 April 2005 14:51
To: William Leijenaar; amsat-bb@amsat.org
Subject: Re: [amsat-bb] FMCW radar question...


Willam,
I would guess that either your FM modulation is too narrow or your receiver
has a narrow pass band. You will always see changes in output at the
detector from the phase interference and doppler from moving targets. A
stationery target is related to the frequency shift related to the roung
trip time mixing with the frequency a the time of arival of the return
signal. 12.4 microseconds per natutical mile was the round trip time used to
calibrate ships radars. You need a triangular waveform to modulate the
oscillator. As a NM is 6000 feet, 60 feet would give you a time of .124
microseconds. If your carrier (output of the Gunn Diode changed 100 KHz per
microsecond, you should have a frequency of 12.4 KHz for a target at 60
feet.

Hope this helps,
Art KC6UQH
----- Original Message -----
From: William Leijenaar <pe1rah@yahoo.com>
To: <amsat-bb@amsat.org>
Sent: Friday, April 22, 2005 6:44 AM
Subject: [amsat-bb] FMCW radar question...


> Hi AMSATs,
>
> Are there any hams that have (design) experience with
> FMCW radar systems ???
>
> I am doing some experiments with a self made system to
> get it working as a distance meter.I have a modulated
> 10GHz signal as source (I see it on Spec.Analyser),
> but the only thing it detects is movement but not
> distance of a none moving object.
>
> It seems that physics is not working right here,
> I am out of options, and looking for sugestions...
>
> It seems a none amsat topic, but for a future moon
> landing mission this radar might be helpfull ;o)
>
> 73
> William
> ---
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