[email protected] wrote:
It seems improving the 2.4 dB of insertion loss of the diplexer would be a better strategy (although not necessarily easy in the space available) than attempting to modify what is very mechanically sound antenna.
73, Joe kk0sd
I am surprised that the duplexer/diplexer (take your pick) has that much loss. Has anyone verified this via a direct measurement (such as via a network analyzer)?
Bob K0NR
I had a great time experimenting with homebrew handheld dual-band antennas for satellite work before I bought an arrow antenna. It is important to note that, as in so many applications, higher antenna gain is not necessarily better. Think of it as a narrower flashlight beam: are you sure you can point the beam directly at the bird? If you lose track of it, how easy will it be to find it again? Moreover, a longer boom means a heavier antenna, and it is amazing how heavy a handheld antenna becomes after 10 minutes!
So I'd say that it is just important in our discussions of antenna gain to discuss pattern. If the handheld satellite antenna's gain is improved by making a pencil-thin front lobe and some side lobes, that's really no good: you'll be too frustrated trying to find the bird.
There are, however, some aspects of the entire receiving system that we can improve. This diplexer number is a bit alarming. I expect it is possible to do better.
Another trick commonly used on home stations is to put a preamp at the antenna output. The low-noise preamp improves the overall noise figure of the system, and compensates for the 'down-stream' losses if put before them, i.e., at the antenna.
As it happens, I've been thinking about how it might be possible to super-charge an arrow antenna with a 435 preamp. I have a small ARR switching preamp handy, but it needs 12v. Some sort of AA battery pack with a charge-pump circuit might do the trick of small enough. Will the added weight on my wrist be worth the improved reception on 435? Only experimentation will tell.
73, Bruce VE9QRP
On Sun, Dec 28, 2008 at 3:22 PM, Bob K0NR (email list) [email protected] wrote:
[email protected] wrote:
It seems improving the 2.4 dB of insertion loss of the diplexer would be a better strategy (although not necessarily easy in the space available) than attempting to modify what is very mechanically sound antenna.
73, Joe kk0sd
I am surprised that the duplexer/diplexer (take your pick) has that much loss. Has anyone verified this via a direct measurement (such as via a network analyzer)?
Bob K0NR
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Bruce,
Putting on a preamp worked wonders (I used a Hamtronics). I'd go in the backyard with it and I put the Arrow on a tripod. It worked out well but I did have desense problems. I finally went to separate antennas, put them on an MFJ tripod and bought a rotor from Radio Shack. I pointed the antennas up at a 30 degree elevation and had my best success this way.
The boom was regular schedule 40 pvc and had quite a bit of sag, the 2 meter antenna was vertical and the 70 cm was horizontal. I then rearranged the antennas to the opposite orientation (I don't remember what my justification was) but I never did get a chance to compare them, life events made operating take a back seat.
I still had desense issues so I finally tossed in a Comet diplexer that I had in the box of goodies....(I don't have a "junk box".
I also had about a 10' run of RG-8x so system losses didn't amount to much.
Just my experience but I recommend use of a diplexer as a filter for the receive....terminate the 2 meter side (I used an old Ethernet 50 ohm terminator).
Good luck!
Tim T K4SHF #35580
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bruce Robertson Sent: Sunday, December 28, 2008 10:41 PM To: Bob K0NR (email list) Cc: [email protected] Subject: [amsat-bb] Re: Fw: ELK or ARROW
I had a great time experimenting with homebrew handheld dual-band antennas for satellite work before I bought an arrow antenna. It is important to note that, as in so many applications, higher antenna gain is not necessarily better. Think of it as a narrower flashlight beam: are you sure you can point the beam directly at the bird? If you lose track of it, how easy will it be to find it again? Moreover, a longer boom means a heavier antenna, and it is amazing how heavy a handheld antenna becomes after 10 minutes!
So I'd say that it is just important in our discussions of antenna gain to discuss pattern. If the handheld satellite antenna's gain is improved by making a pencil-thin front lobe and some side lobes, that's really no good: you'll be too frustrated trying to find the bird.
There are, however, some aspects of the entire receiving system that we can improve. This diplexer number is a bit alarming. I expect it is possible to do better.
Another trick commonly used on home stations is to put a preamp at the antenna output. The low-noise preamp improves the overall noise figure of the system, and compensates for the 'down-stream' losses if put before them, i.e., at the antenna.
As it happens, I've been thinking about how it might be possible to super-charge an arrow antenna with a 435 preamp. I have a small ARR switching preamp handy, but it needs 12v. Some sort of AA battery pack with a charge-pump circuit might do the trick of small enough. Will the added weight on my wrist be worth the improved reception on 435? Only experimentation will tell.
73, Bruce VE9QRP
On Sun, Dec 28, 2008 at 3:22 PM, Bob K0NR (email list) [email protected] wrote:
[email protected] wrote:
It seems improving the 2.4 dB of insertion loss of the diplexer would be a better strategy (although not necessarily easy in the space available) than attempting to modify what is very mechanically sound
antenna.
73, Joe kk0sd
I am surprised that the duplexer/diplexer (take your pick) has that much loss. Has anyone verified this via a direct measurement (such as via a network analyzer)?
Bob K0NR
Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
_______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Bob K0NR (email list) wrote:
[email protected] wrote:
It seems improving the 2.4 dB of insertion loss of the diplexer would be a better strategy (although not necessarily easy in the space available) than attempting to modify what is very mechanically sound antenna.
73, Joe kk0sd
I am surprised that the duplexer/diplexer (take your pick) has that much loss. Has anyone verified this via a direct measurement (such as via a network analyzer)?
Bob K0NR
I don't have a network analyzer handy, so I did an A/B test driving the Power Meter on my HP 8920A using a handheld radio. At 435 MHz, the measured power with just a cable connection is 2.5 W. With the Arrow duplexor inserted, the power is 1.8 W. This implies a loss of 10 log (1.8 /2.5) = -1.4 dB, more than I would have expected.
How accurate is this measurement? I dunno, probably no worse than 0.5 dB. This deserves further investigation.
73, Bob K0NR
participants (3)
-
Bob K0NR (email list) -
Bruce Robertson -
Tim Tapio