[AMPS] Propeties of plastics at 10 GHz

[Rich Measures]

>
>> >Sorry this is not stictly about amps, but I guess someone here might
>> >know the answer.
>> >
>> >We have a student working on using a 10 GHz transmitter (burgler alarm
>> >type, using a 10GHz Gunn diode) and detector (Schottky diode) to measure
>> >attenuation caused by cloathing soaked with water (to determine the
>> >amount of water in the cloathing). We need to find a plastic (or other
>> >material that we can machine things from) that *absorbs* microwave
>> >energy at 10 GHz. I don't want a good reflector (metals), but something
>> >that will attenuate by absorption (ie it would get hot if we used enough
>> >power).
>> >
>> Nylon.  Vinyl.  Delrin.
>> 
>> Rich...
>> 
>> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>------------
>Howdy,
>Nylon, vinyl and delrin are poor absorbers at 10 GHz.  

This issue came up during the "grate vhf parasitics debate", so I went to 
the local plastics distributor to get some info. on dissipation factor - 
a.k.a. D-factor  Nylon has a high D-factor at 1MHz and an even higher 
D-factor at 10MHz.   The various vinyls and Delrin have a lower D-factor, 
however, not nearly as low as the stryrenes, polyethelynes or Teflon..  . 
 .  I had PVC water pipe catch fire at the end of a 40m dipole.  I had a 
40m dipole that was supported with nylon line reliably decend to the 
ground when the linear amplifier was switched on.  .  Does it seem likely 
that nylon would have high absorption at 7MHz and poor absorption at 
10GHz.?  - - - To check it out, put a styrene cup half full of water, 
along with a sample of the plastic you want test, in a microwave oven and 
blast away for a dozen or so seconds.  .  
-  later

> They do work well if you want to change the phase of a signal @ 10 GHz.
>
>Cuming Corporation, 230 Bodwell St., Avon, Ma 02322 manufactures
>machinable, absorptive materials that will do what you want.
>
>Good luck,
>Bob, W5AH



Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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