[eagle] Re: Another idea on phased array configuration

Dick Jansson-rr rjansson at cfl.rr.com
Thu Apr 26 09:34:29 PDT 2007


And thermally that all is pretty bad (being as civilized as I can say it)!
We cannot allow ourselves be sucked into such dreadful thermal situations.
 
Dick Jansson, KD1K
kd1k at amsat.org 
kd1k at arrl.net 
---------------------------
-----Original Message-----
From: eagle-bounces at amsat.org [mailto:eagle-bounces at amsat.org] On Behalf Of
Louis McFadin
Sent: Thursday, 26 April, 2007 1508
To: K3IO at verizon.net
Cc: AMSAT Eagle
Subject: [eagle] Re: Another idea on phased array configuration


For 43 of the Hittite devices it would take 132 w to deliver 43w of RF.
This doesn't count the circuitry needed to drive the finals or other
spacecraft requirements. 
This will also present a huge thermal problem with the need to dump around
100w of heat on the top of the spacecraft.
At least 250w of solar capacity would be needed to support this based on
current requirements.

On Apr 26, 2007, at 1:08 AM, Tom Clark, K3IO wrote:


Bill Ress wrote: 

Hi Tom, 

Thanks for sharing your thoughts on the phased array approach. 

I especially appreciated your block diagrams which really helped. I'm
sorting through the approach and will likely have some questions. 

Regarding amplifiers for 5.7 GHz, Sirenza has a 1/4 watt for $4.80. It draws
165mA @ 5V or 7 amps for 43 of them. 

Now here's the real heartburn device. The Hittite HMC409LP4 (I think the one
you referred to) provides just over 1 watt, costs $8.52 (not bad at all) but
runs 615mA at 5V - or  26 Amps for 43 antennas. If that input power doesn't
bother anyone - there's part of our design! 

I've never heard any estimates of what DC power Eagle is planning to
deliver. Is that figure available yet? 

Thanks again Tom for your time and thoughts. 

Regards...Bill - N6GHz 


Bill -- it was the Hittite HMC408 that we looked at. We (N4HY, W3GPS & I)
got one of the HMC408 eval boards and tested it in Sep.'05. I presented a
quick summary of our tests at the Eagle working group meeting in Pittsburgh
in Oct.'05. I looked around for my PowerPoint presentation and found it; it
can be gleaned on my "freebie" website at
http://mysite.verizon.net/w3iwi/HMC408.ppt. The presentation, as posted, has
one glaring error: the Hittite brick is missing from Slide #7. It's pretty
obvious, bur it is a block between the DB6NT  upconverter and the -16 dB
directional coupler. I never had a reason to re-present the talk, so I never
bothered to fix the drawing.

Anyway, the main conclusions from our "quickie" tests were


1.	It worked as advertised in the data sheet (within ~ 1 dB which was
comparable to our measurement accuracy). 

2.	We concluded that we could affect you could optimize efficiency at
any given power output level by tweaking Vctl. 


3.	The peak DC>RF efficiency we saw was ~ 22% for Vctl in the 3.5-4V
range and Vcc1=Vcc2=5V.


4.	There is a possibility of doing even better by doing a more careful
optimization of Vcc1 and Vctl. I suspect that Vcc2 needs to be the
recommended 5V. This is especially true if we are going to be able to use
constant envelope BPSK.  (i.e. something approaching Class-C). 

5.	Any amplifier can be easily shut down by setting Vctl=0. 

Let's hope we can find a more efficient amplifier chip!

73, Tom


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