[amsat-bb] Re: Almost There

Jim Jerzycke kq6ea at verizon.net
Sat Jan 4 17:55:11 PST 2014

Getting rid of the diplexer will reduce the loss, but not improve the 
gain. The gain is dependent on the design of the antenna.

73, Jim  KQ6EA

Adding a preamp at the antenna is always a good idea for satellite use.

On 01/05/2014 12:42 AM, Joel Black wrote:
> After a rocky start to my Christmas Vacation (I fell off a ladder 
> while pruning limbs from a tree - nothing broken, just banged up and 
> bruised), I almost have my satellite station back on the air.
> After doing some selling and horse-trading, I am back in possession of 
> my FT-847 that I sold to my dad.
> After cleaning out my storage building, I found a couple of fairly 
> long runs of LMR400UF. I need to measure them, but I think it is more 
> than enough to get me outside and up the mast.
> I also have a U-100 control box thanks to someone on the list.
> I operate an iMac with Mac OS X 10.9.1 so, for now, I am using SatPC32 
> on my virtual machine. I have played around with MacDopplerPro, but it 
> locks up on my computer continuously. I don't know if it has something 
> to do with the USB-to-serial converter (I *do* have a null modem cable 
> between the USB-to-serial converter and the FT-847), or if MDP is just 
> limited in the unregistered version. The USB adapter works fine with 
> my K3.
> Let me ask a question about the Arrow Antenna. Someone mentioned Elk 
> Antennas and, while I'm sure it's a fine product, I am already in 
> possession of the Arrow. I've done a lot of reading and without 
> getting into the arguments about Arrow vs. Elk and length of elements, 
> etc., element isolation, and published vs. unpublished gain amounts 
> let me tell you what I'm thinking:
> First, I'm going to eliminate the diplexer. I will not need it for one 
> thing. For another, it's limited to 10 W max input. From what I have 
> read, my gain will be increased quite a bit. I don't remember the 
> exact amount, but it's quite dramatic.
> Second, the feed on the Arrow is a gamma match. From my reading, and 
> I'm no engineer, for a gamma match to work properly the element(s) (at 
> least the driven element) needs to be grounded. That's fine and, 
> again, I don't want to get into the "why's" I just want to make sure 
> I'm correct. Therefore, my question is:
> Is there any reason I cannot turn the driven element 90 degrees to 
> allow for a better connection to the BNC connector? Maybe not even 90 
> degrees, but enough to get to the BNC connector without the male 
> connector on the cable touching the boom. I want to weatherproof those 
> connections. What I'd like to do after I turn the gamma match is feed 
> it with a very short length of LMR240 and then into a preamp. After 
> the preamp, I'll have the LMR400UF to run to the FT-847. Most gamma 
> matches I see on commercial antennas are on the side of the antenna - 
> if horizontal, they're below (or above) the boom; if vertical, it's 
> off to one side. The Arrow is the only antenna I've seen with a gamma 
> match on which the gamma match is not to one side or the other of the 
> boom. I hope I'm making sense.
> Anyway, I wanted to let those folks who helped out know that I 
> appreciate it and that I'm much closer to being back on the birds than 
> I was a few weeks ago.
> 73,
> Joel - W4JBB
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