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Re: Elk Antennas for HTs?



On Wed, Oct 20, 2004 at 10:08:51AM -0700, Emily Clarke wrote:

| The fact that the two antennas in the Arrow have two connectors is not
| because they are 90 degrees out of phase

Is `out of phase' the right term here?

I assume that the reason that the two antennas are 90 degrees apart
from each other is to provide the maximum possible isolation between
the two antennas (after all, the dimensions were carefully calculated.
We don't want to mess that up at all) and yet keep the physical size
as small as possible.

I assume that the reason there are two connectors is because there's
two antennas, for two bands.  You may be using two radios with it.
Also, I would expect that putting a T connector in there rather than a
duplexer (for use with a single radio with a single antenna jack)
might waste some power, as the 2m yagi would be approximately resonant
at 70cm, but it's director/reflector dimensions would be all wrong
causing a wierd pattern that's probably not what you want.

| The primary use of the duplexer is isolation.

Of course.  However, I don't see how an Arrow antenna with a duplexer
(probably built into the handle) is fundamentally any different than
the Elk antenna without one.

(Of course, they're different types of antennas, with different
specifications, but ultimately, both setups provide relatively high
gains in the 2m and 70cm bands, and both provide one connection for
your radio.)

| The original statement was about the IC-W32A which I own (I do not
| own the other radios you mention) so I can't speak for their built
| in duplexers.  However I don't believe the FT-530 is full duplex.

It is.

| I seem to recall it turns off the second receiver whenever you
| transmit

It does not.
 
| My experience with the Elk and the W32A in FULL duplex mode is that
| it desenses the receiver when you are transmitting so you cannot
| hear yourself coming back down on the downlink frequency.

Since you're transmitting and receiving on the same wire coming out of
your radio, I'm not really sure how an external duplexer is going to
prevent this -- if the duplexer inside your radio cannot provide
adequate isolation, I don't see how an external duplexer can do it.

| I have tried the BNC T connector method mentioned above rather than
| the duplexer with the Arrow and it desenses, though not as bad as
| the Elk did since the 90 degree difference in transmit and receive
| antennas offers a little isolation.  With a duplexer you get
| additional isolation and it doesn't desense.

I wonder if the problem you had with the Elk antenna was a higher SWR
(higher than with the Arrow antenna) on your transmitting band -- that
would send more signal back to the radio, which would cause more
signal to get past the internal duplexer, desensing more ...

I'm looking to make an antenna for satellite work.  (I could buy one,
but it seems simple enough to make one.)  I was thinking of the arrow
(two yagis at 90 degrees) design, but the log periodic used by the Elk
certainly seems simpler and more portable, and no duplexer needed (for
my setup) is a nice bonus.  (Yes, I realize that I could use a T
connector, but I think that will cause problems as I mentioned
before.)  I'm trying to decide with which way to go (or maybe I should
just do both :)

It's funny about antennas ... I've found them fascinating, and have
read just about everything I've found on them, but the more I learn,
the more I realize I don't know.  This is true about most things, I
know, but seems much more pronounced with antennas ... 

--
Doug McLaren, dougmc@frenzy.com, AD5RH
I do whatever my rice krispies tell me to.
----
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