[amsat-bb] new sats and 23cm
zleffke at vt.edu
Wed Aug 5 05:12:01 UTC 2015
Directive Systems and engineering has loop yagis specifically for the amateur satellite service in this band. It is what we will be using in the Virginia Tech ground station. No feedback yet on performance (we're not up yet) but they look very well made and the folks at the company are fantastic and they have a great reputation with their antennas at microwave and up. They are fairly compact and lightweight as well and could likely be added to a G5500 style setup with ease and minimal additional strain on the motors.
I'm not aware of any omnis for this band off the top of my head, but being that it is an uplink only allocation, lack of gain and increased path loss could be made up for with power (bearing in mind the recent threads on proper uplink power levels). Consider though that there is about 18.8dB and 9.7dB of additional path loss over VHF and UHF respectively. Assuming similar rx gains and noise performance on the bird at 23cm, as well as atmo/iono losses, that additional loss will have to be overcome on the ground, either with increased antenna gains, or with increased power. Given that the 9100 makes about 10W on 23cm, it may be time for a decision. a) 23cm module plus fairly beefy amp plus homebrew omni, or b) 23cm module plus rotator system plus well built (and factory tuned) yagi.
Personally, I'd recommend option b with rotator plus beam plus lower power, mainly because antenna gain is easy/cheap at 23cm and PAs can be expensive/tricky at 23cm, but I have access to existing rotator systems which bias my opinions.
My two cents....
Also it might be interesting to see some more rigorous analysis and antenna designs for 23cm (omnis and beams). Maybe comparisons of various omnis and various beams and how they affect G/T (imagine a cute little lindenblad or turnstyle or eggbeater for 23cm and how physically small it would be compared to what we are used to at VHF/UHF, it would be roughly a third of the size of its UHF equivalent!). Once we can get some details from the Fox engineering crew or Ops crew on the expected performance of the uplink receiver on 23cm, could make for a good article or two for the Journal (especially the bit on 'microwave omnis' and their feasibility, I'm sure the eng/ops crew has or will have a solid handle on the overall receiver performance and link budgets).
On Aug 4, 2015 11:32 AM, David <dwarnberg at verizon.net> wrote:
> I see lots of talk about some new sats going up that will be utilizing 23cm.
> so I have some questions.. first let me explain what I have setup
> 1) Icom IC-9100 (23cm module not added yet)
> 2) M2 eggbeaters (70cm and 2m) with preamps
> So I am contemplating adding the 23cm add on for the 9100 but perplexed
> about an antenna. suggestions?
> David, KK4QOE
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