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'[EE]: Circulator'
2001\12\15@172317 by Sean H. Breheny

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Hi all,

Does anyone have (or know where I could find at a reasonable price) a
circulator for the 3.45 GHz amateur band? I'd prefer one with some type of
coax connectors, not waveguide. I'm having a heck of a time trying to find
one of these! Can't find any surplus or used, and the one company I
contacted so far which makes them has not returned my email (presumably
because I'm not a high volume buyer).

Thanks,

Sean

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2001\12\15@193217 by Bob Barr

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On Sat, 15 Dec 2001 17:21:06 -0500, "Sean H. Breheny" wrote:

>Hi all,
>
>Does anyone have (or know where I could find at a reasonable price) a
>circulator for the 3.45 GHz amateur band? I'd prefer one with some type of
>coax connectors, not waveguide. I'm having a heck of a time trying to find
>one of these! Can't find any surplus or used, and the one company I
>contacted so far which makes them has not returned my email (presumably
>because I'm not a high volume buyer).
>

Have you tried eBay? They always seem to have lots of RF stuff there.

Regards, Bob

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2001\12\15@195131 by Sean H. Breheny

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Hi Bob,

Thanks for the suggestion but yes, I have been monitoring eBay for this for
about two months. There are a number of circulators which keep showing up
(apparently not too many people want circulators) but none for this frequency.

Sean

At 12:18 AM 12/16/01 +0000, you wrote:
{Quote hidden}

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2001\12\15@210802 by Jon Baker

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Forgive my naivety. but what is a circulator exactly? Its not a term I've
come accross before.

Jon

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2001\12\15@225840 by Sean H. Breheny

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Hi Jon,

It's an RF device that has at least three ports (but can have more). The
ports are numbered. RF energy entering at one port can only go "around" the
sequence of ports in one direction. So, for example, if the "circulation
direction" is from 1 to 2 to 3, then RF entering at port one can travel to
port 2 but not directly to port 3, it will only go to port 3 if it is not
completely absorbed at port 2 (i.e., if there isn't a correct match at port
2). RF energy entering at port 2 goes directly to port 3 but not directly
to port 1, etc. A more concise way of saying this might be "RF entering at
a particular port is directed completely to the next port in the
circulation direction, provided that next port is correctly terminated."

In practice, they work imperfectly and there is some insertion loss and
also some RF energy does go around the wrong way (even with properly
terminated ports), but it is usually attenuated by about 20dB (called the
isolation).

They are used in some situations to allow a transmitter and receiver to be
connected to the same antenna. In the above example, if you attach the
transmitter to port 1, the antenna to port 2 and the receiver to port 3,
theoretically all of the TX power would go to the antenna and all the RX
power would go to the RX.

They are usually made using ferrite materials which cause Faraday rotation
(that is, a rotation of the polarization of the wave which is different as
it goes through one direction versus the other direction). This
non-reciprocal behavior is used (along with polarizers, I think) to allow
propagation in one direction but not the other.

In my particular instance, although I have way too many irons in the fire
already, I am gathering parts that I need for my amateur weather radar
project (which I mentioned on the list a few months ago). The circulator
would be the main T/R "switch" for the system, allowing the TX and RX to be
connected to the same antenna. I already have a 20 Watt 3.45 GHz amplifier,
some microwave cables, and a 3 foot parabolic dish. I also just completed
the design of the local oscillator unit for the system (a dual PLL,
producing 640MHz and 2.8GHz signals) and I've got all the parts. I plan to
assemble and test it over my Christmas break coming up.

Sean


At 01:59 AM 12/16/01 +0000, you wrote:
>Forgive my naivety. but what is a circulator exactly? Its not a term I've
>come accross before.
>
>Jon
>
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2001\12\16@075114 by Jon Baker

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Sean,

Thanks for that - a good explanation. Your weather radar project- are you
just detecting cloud levels.. or are you going the whole 9 yeards and trying
to make a doppler system :)

Jon

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2001\12\16@092714 by Friedel Bruening

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You can try http://www.ukw-berichte.de which a german amateur type
magazin about VHF/UHF/SHF. There i have seen all kinds
of stuff of this nature, there are lots of links to providers,
it´s in English to, with some providers you may have
language trouble, if so you may contact me, so I will
help you out.
The magazin I would rate as very good BTW, but it´s in German.

Friedel

At 05:21 p.m. 15/12/01 -0500, you wrote:
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2001\12\16@094603 by Sean H. Breheny

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Hi Jon,

Thanks, I'm glad you liked it! I'm trying to control my feature creep
tendencies, so I'm just going for an incoherent, non-Doppler radar right
now. However, I plan on providing an RX IF output jack and TX IF input
jack, so that it would be easier, later on, to add a coherent signal
processor if I ever get around to it. The LO board I just designed should
be very stable and fairly low phase noise, so I think it might be good
enough as a basis for a coherent system.

Essentially, I'm hoping for something that can map out moderate to heavy
rain within a several tens of mile radius. My biggest limiting factors are
a 20 Watt peak output power (only affordable amplifier I could find) and
the 3 foot dish (need to fit it in my car).

Sean

At 12:43 PM 12/16/01 +0000, you wrote:
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2001\12\17@025456 by Vasile Surducan

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Sean, maybe you will laugh, but my brother which is an microwave
specialist have built a 10 GHz circulator himself. Is not an easy job, it
required a lot of fine mechanics but is perfectly possible, using amateur
working conditions. ( plotter, masks etc, ceramic support and ferrite )

Just a thought,
Regards, Vasile

On Sat, 15 Dec 2001, Sean H. Breheny wrote:

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