Probably a stupid question, but...
 

Anyone have any idea as to the probable performance characteristics of two
whip 40" whip antennas mounted approx. six inches apart, and used for
receiving shortwave, primarily between 6 MHz and 12 MHz? Would they be more
receptive to a signal approaching f/b, as opposed to s/s? Just wondering...
Hoping someone can offer some advice as to whether they would be in any way
directional.

Thanks for any replies,

Dave

Probably a stupid question, but...
 

Dave wrote:
Anyone have any idea as to the probable performance characteristics of two
whip 40" whip antennas mounted approx. six inches apart, and used for
receiving shortwave, primarily between 6 MHz and 12 MHz? Would they be more
receptive to a signal approaching f/b, as opposed to s/s? Just wondering...
Hoping someone can offer some advice as to whether they would be in any way
directional.

They would be directional at the frequency where
6 inches is 1/8 wavelength. :-)
--
73, Cecil http://www.w5dxp.com

Probably a stupid question, but...
 

"Cecil Moore" wrote in message
...
Dave wrote:
Anyone have any idea as to the probable performance characteristics of
two whip 40" whip antennas mounted approx. six inches apart, and used for
receiving shortwave, primarily between 6 MHz and 12 MHz? Would they be
more receptive to a signal approaching f/b, as opposed to s/s? Just
wondering... Hoping someone can offer some advice as to whether they
would be in any way directional.

They would be directional at the frequency where
6 inches is 1/8 wavelength. :-)
--
73, Cecil http://www.w5dxp.com

Hey Cecil, thanks for the reply.

Hmm. So, correct me if I'm wrong, but from what you're saying they would
actually have some directional characteristics at approx. 2.5 MHz. What if
I angled them apart at, say, 45 degrees? That would, I think, put the tops
about 57 inches apart, and the two whips at right angles to each other. Any
ideas what that would do? Or, if I flattened them out in opposite
directions? I need an ARRL Antenna Handbook, only I wouldn't know what to
look up...

Do appreciate your reply. Gives me something to think about...

Dave

Probably a stupid question, but...
 

"Dave" wrote in
:

Anyone have any idea as to the probable performance characteristics of
two whip 40" whip antennas mounted approx. six inches apart, and used
for receiving shortwave, primarily between 6 MHz and 12 MHz? Would
they be more receptive to a signal approaching f/b, as opposed to s/s?
Just wondering... Hoping someone can offer some advice as to whether
they would be in any way directional.

If they are simply in parallel, they would not have much directivity. But
if one were to be phase-inverted with respect the other, there would be a
strong null along the bisector of the line joining them.

The gain at 9mhz is on the order of -30dbi, though so you will need a good
receiver or even a preamp.


--
Dave Oldridge+
ICQ 1800667

Probably a stupid question, but...
 

"Dave Oldridge" wrote in message
9...
"Dave" wrote in
:

Anyone have any idea as to the probable performance characteristics of
two whip 40" whip antennas mounted approx. six inches apart, and used
for receiving shortwave, primarily between 6 MHz and 12 MHz? Would
they be more receptive to a signal approaching f/b, as opposed to s/s?
Just wondering... Hoping someone can offer some advice as to whether
they would be in any way directional.

If they are simply in parallel, they would not have much directivity. But
if one were to be phase-inverted with respect the other, there would be a
strong null along the bisector of the line joining them.

The gain at 9mhz is on the order of -30dbi, though so you will need a good
receiver or even a preamp.


--
Dave Oldridge+
ICQ 1800667

Aha! A strong (or deep) null! That's actually what I'm looking for. So,
what would I look up to start learning how to set one up as phase-inverted?
I have a copy of Joe Carr's Antenna Handbook (think that's the title), would
it have anything on such a setup, do you think? What would I look for in
the ARRL Antenna Handbook? Does this type of setup have a name to search on?

And yes, compared to my 110' longwire, the signal is miniscule. But I'm
working on that.

Thank you so much, Dave, for this input. Now I have some idea as to what I
am looking for, (I *think*).

Much appreciated.

Dave Beane

Probably a stupid question, but...
 

Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able
to fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound
effect on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Probably a stupid question, but...
 

"Roy Lewallen" wrote in message
...
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able to
fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound effect
on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Found my copy of Joe Carr's Practical Antenna Handbook, and re-read the
section on phasing verticle antennas. I believe you. Back to square one,
which was the thought that a loop was probably my best bet (I had come to
that conclusion a while back, but forgot why.)

Did try a shielded loop once upon a time, but didn't feel it gave me
anything to look forward to. Guess I'll dig it out and try it again. Will
try shielding it with copper "tape" and see what that buys me. I did try a
piece of coax wound in a triple-turn loop to give me 2.5 or 3 uH with which
to tune, with the shield cut away to expose the center conductor for a
couple inches, but didn't feel this offered anything either. Not sure what
I'll do. Poke around and try different things until I find something that
works better than the rest. Any ideas? I'm all ears. I tried the whips
because I had them on hand, and they were easy to install. Seems I read
somewhere that contrary to conventional wisdom, the shield on a shielded
loop doesn't actually shield at all, but becomes the antenna element.
Anyone know anything about that line of thought? I obviously know nothing,
and am trying to learn. Just don't know where to focus my energies.

Thanks,

Dave

Probably a stupid question, but...
 

Dave wrote:
. . .
. . .Seems I read
somewhere that contrary to conventional wisdom, the shield on a shielded
loop doesn't actually shield at all, but becomes the antenna element.
Anyone know anything about that line of thought? I obviously know nothing,
and am trying to learn. Just don't know where to focus my energies.

That's been discussed on this newsgroup a number of times. You should be
able to find the relevant threads via groups.google.com.

Yes, the "shield" doesn't shield the antenna -- in fact, the outside of
the "shield" *is* the antenna. What it does is aid in balancing the
antenna, reducing common mode pickup which can reduce the null depth.
"Conventional wisdom" that holds otherwise isn't wisdom at all, but a
lack of understanding of some basic electromagnetic principles.

There's undoubtedly a massive amount of information easily available on
the web regarding building and using small loop antennas. All you have
to do is ignore the ubiquitous "conventional wisdom" explanations of how
a "shielded" loop operates.

Roy Lewallen, W7EL

Probably a stupid question, but...
 

"Dave" wrote in message
...

"Cecil Moore" wrote in message
...
Dave wrote:
Anyone have any idea as to the probable performance characteristics of
two whip 40" whip antennas mounted approx. six inches apart, and used
for receiving shortwave, primarily between 6 MHz and 12 MHz? Would they
be more receptive to a signal approaching f/b, as opposed to s/s? Just
wondering... Hoping someone can offer some advice as to whether they
would be in any way directional.

They would be directional at the frequency where
6 inches is 1/8 wavelength. :-)
--
73, Cecil http://www.w5dxp.com

Hey Cecil, thanks for the reply.

Hmm. So, correct me if I'm wrong, but from what you're saying they would
actually have some directional characteristics at approx. 2.5 MHz.

I don't get that number at all. Splitting the difference between 6 and 12
Mhz, say
9 Mhz, an 1/8th wavelength distance would be about 4 meters.
Anybody have a url of a page that shows receive pattern of two antennas at
different
spacings, 1/8, 1/4, 3/8, 1/2 wavelengths?
Dave, I recommend you download the demo version of EZNEC, it won't take
to long to model a couple of verticals at different spacing.
Mike

Probably a stupid question, but...
 

Dave wrote:
"Cecil Moore" wrote in message
They would be directional at the frequency where
6 inches is 1/8 wavelength. :-)
--
Hmm. So, correct me if I'm wrong, but from what you're saying they would
actually have some directional characteristics at approx. 2.5 MHz.

Make that 250 MHz. If 6 inches is 1/8WL, then one
wavelength would be 4 feet. 984/4 = 250 MHz.
--
73, Cecil http://www.w5dxp.com