[time-nuts] Choke Ring Pictures
Bruce Griffiths
bruce.griffiths at xtra.co.nz
Mon Mar 15 20:34:44 UTC 2010
For some idea of the considerations involved in selecting materials for
and designing a radome see:
http://ia331316.us.archive.org/0/items/radarscannersand033384mbp/radarscannersand033384mbp.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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