[amsat-bb] Lindenblad or DCA???

[Hans (BX2ABT)]

Hello Joe,

Thanks for the reply, appreciate it.

Yes, the phasing harness is different, but my guess was that this 
shouldn't make a lot of difference as long as you get the 90 degree 
phase and the impedance right. If you look at the radiation patterns for 
both then they are nearly identical, hence my question if they are not 
one and the same thing.

It came up here because I have two DCAs right now, one for 2m, one for 
70cm, both RHCP, no pre-amps. I do hear some birds, but signals are very 
weak. The 2m one works fine when receiving the NOAA wx sats, so I was 
wondering if the 30 degree angle of the Lindenblad would be better for 
amateur sats. I lack the knowledge to understand the difference between, 
what you say, the geosynchronous orbit of NOAA sats and the LEO orbits 
of our sats. NOAA wx sats are also LEO sats, not? I'll see if Google 
turns up something there.

It's easy for me to change the tilt of my DCAs to 30 degrees, so I'll 
try that this week. Should be a nice experiment.

73 de Hans
BX2ABT


> Hans,
>
> Here are links with antenna patterns for the DCA:
>
> https://drive.google.com/file/d/0B0Dkk87YYl-xX2gzLXk5MHZKVU0/view
>
> and the EZ-Lindenblad:
>
> http://www.amsat.org/wordpress/wp-content/uploads/2015/08/An-EZ-Lindenblad-Antenna-for-2-Meters2.pdf
>
> The difference is in the lengths of the "RG-59 (75ohm) phasing harness"
> and dipoles to achieve a 50 ohm impedance at the required frequency.
>
> The angle of the crossbooms affects the directivity of the antenna, in
> the examples given, 60 degrees for a NOAA satellite in a geosynchronous
> orbit and 30 degrees for a LEO orbit.
>
> The only differences I see are the 50 ohm load feedpoint and the
> Lindenblad dipoles are not exactly in the same plane as the DCA.
>
> -73, Joe Spier, K6WAO
> President, AMSAT