[time-nuts] Choke Ring Pictures

Bob Camp lists at rtty.us
Mon Mar 15 21:21:08 UTC 2010


Hi

If I ever need to duplicate the raydome on a B-29 I now know right where to
look.

===========

Lots of math and some crazy looking plots of what happens as you start going
at off angles to the material. The problem certainly isn't just one of loss
since the raydome acts as sort of a lens over the antenna. 

No matter what, raydome is a better thing than a bird sitting on top of the
antenna. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bruce Griffiths
Sent: Monday, March 15, 2010 4:35 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Choke Ring Pictures

For some idea of the considerations involved in selecting materials for 
and designing a radome see:
http://ia331316.us.archive.org/0/items/radarscannersand033384mbp/radarscanne
rsand033384mbp.pdf 


A list of the properties of some dielectrics at microwave frequencies in 
inluded.


Bruce

Bob Camp wrote:
> Hi
>
> Any idea what the funnel was made out of? Some plastics aren't real great
at
> microwaves...
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Brian Kirby
> Sent: Sunday, March 14, 2010 8:50 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Choke Ring Pictures
>
> The home made choke ring was calculated and the pie/cake pans came
> close.  I think somebody all ready pointed at it, but Unavco or NASA had
> the dimensions to about 6 or 8 common choke ring reflectors on line.
>
> They are aluminum cake pans - I bought them in a crafts store.  They are
> one inch apart between the rings.   They are 2 inches deep at the rims.
> The outside pan is 12 inches (measured inside).  Next is 10 inch,  then
> 8 inch, then 6 inch, and 4 inch.
>
> When making them, I found the center of each pan and then drilled them.
> Then I used a bolt to hold them all together except for the very center
> unit.  Then I drilled two holes about and inch from the center and used
> thin long bolts to  attach them to a piece of square tubing on the
> bottom.   The alignment bolt was removed from the center hole and
> drilled out larger to pass the antenna coax thru.    The very center
> pan, I used epoxies to glue the antenna too and I used a clamp to hold
> it in place.   Then the  coax was pass thru a hole I drilled out thru
> the center holes of the other pans.   Then I glued the antenna pan to
> the other pans and used several blocks of wood to center the pan and a
> big piece of pipe and weights as a clamp to hold it down while it was
> curing.   The square tubing was aligned into a  laser level mount and
> epoxied and that allows the unit to be attached to a tripod.  The mount
> has three adjusting screws that allows the antenna to be leveled.   I
> used the units in pairs when surveying and always aligned then north in
> an attempt to bias out centering differences.
>
> The first unit mounted on the house roof did have a drainage problem the
> first time it rained.  I drilled 1/8 holes inside of each ring to let it
> run out.  That was not the worst problem.  A bird decided it would make
> a good home and started building a nest on it when I went on vacation.
> I bought a large plastic funnel and inverted it and glued it inside of
> the outer ring to stop that.
>
> The antenna is the common Antenna97 from Motorola, the coax was cut at
> about one foot (I think it was originally 18 feet long) and a connector
> was attached.  I then used a very low loss coax (1/2 inch heliax) about
> 40 feet long to bring it into the basement.
>
> Brian - KD4FM
>
>
>
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