[amsat-bb] Re: Question adding RHCP to Cheap Yagi

[Howard Long]

Hi Curt

There are several ways to skin the same cat.

Although they are fed in phase, they are orthogonally mounted and with their
spatial separation a 90 degree phase delay is created, thus creating CP.

If the elements are still orthogonal but are at the same location along the
boom, then the delay would need to be inserted electrically, with an
electrical 1/4 wave section of 50 ohm coax. Some CP antennas use a
combination of both spatial and electrical phase difference.

To switch RHCP to LHCP can be achived by any of the following three means:

O Insert an additional 180 degree electrical delay between one arm of the
power splitter and the antenna, with an electrical lambda/2 50 ohm coax
section;

O Physically move one set of elements 180 degrees forward or behind;

O Turn one of the driven elements 180 degrees so the loop is on the other
side of the antenna, but maintain the same electrical connections.

This may (of may not!) help... http://www.g6lvb.com/remotepolarization.htm

It takes a bit of lateral thinking, but once you've figured it out it's a
bit like learning to ride a bike in that you don't forget, although in later
years I find one may become a little wobbly.

73, Howard G6LVB


-----Original Message-----
From: Curt Nixon [mailto:cptcurt at flash.net] 
Sent: 02 January 2009 16:50
To: Howard Long
Cc: 'AMSAT-BB'
Subject: Re: [amsat-bb] Question adding RHCP to Cheap Yagi

Hi Howard:

Thanks..I've looked at alot of your info on-line--especially the sub-500GBP
AO-40 setup. 

I guess I still don't get it..if I just feed them in-phase with both
connections same polarity, what controls RH v. LH?

Or is it RH if the front half loop is to the right and LH if the front
half-loop is to the left?

Thanks

Curt

Too cold to not get it right on the first try!! 



Howard Long wrote:
> Hi Curt.
>
> Either way will work.
>
> http://www.g6lvb.com/AO-40%2070cm%20uplink%20antenna.htm
>
> I have had superb success with mine, in fact during the days of AO-40 
> I worked the world with it as an uplink antenna with 50W.
>
> http://www.g6lvb.com/3A2%20ops.htm
> http://www.g6lvb.com/dayton_demo_2002.htm
>
> 73, Howard G6LVB
>
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] 
> On Behalf Of Curt Nixon
> Sent: 02 January 2009 15:19
> To: AMSAT-BB
> Subject: [amsat-bb] Question adding RHCP to Cheap Yagi
>
> Good Morning All:
>
> I've been using a 10el version of Kent Britain's Cheap yagi for my 
> 70cm downlink antenna.  It suffers from deep fades so I am going to 
> add the second yagi with physical offset to get to RHCP in the x config.
>
> Question is:
>
> normally I would reverse the coax connections to a dipole driver but 
> this is a hairpin (half of a folded dipole. )
>
> Do I reverse the connections as normal?  Kents instructions just say 
> offset the elements and feed in phase.
>
> Thanks
>
> Curt
> KU8L
>
>
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