Lostgallifreyan wrote:
John S wrote in :

The hallmark of a rhombic is that is long compared to the wavelength of
operation in order to achieve directionality (that is, gain in a
particular direction).


It's totally new to me. I just looked at Google images for a few minutes.
Nice looking constructions. The thing that struck me most was your
description of directionality, non-resonance (at lest, not standing wave),
long compared to wavelength, and termination by a resistance. All these
things can be said of a Bevarage too, but they're obviously very different
too. I don't know what the relation is.

http://en.wikipedia.org/wiki/Rhombic_antenna

http://www.w8ji.com/rhombic_antennas.htm

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.

Otherwise people these days use log-periodics for better performance
and a lot smaller footprint.


--
Jim Pennino

wrote in :

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.


Ok, that rules me out right there. I can maybe manage a long wire laid out
temporarily, but for large scale that's about it for me.

Lostgallifreyan wrote:
wrote in :

A fair antenna is you have a bunch of telephone poles and a huge piece
of empty ground.


Ok, that rules me out right there. I can maybe manage a long wire laid out
temporarily, but for large scale that's about it for me.

Decades ago I was affiliated with an Army MARS station that had inherited
a WWII rhombic array of 4 antennas for 360 coverage that worked fairly
well from about 5 MHz and up.

The thing seemed to be a lightning magenet during thunderstorm season
and sections of the wire that had been vaporized required regular
replacement.

Eventually the Army decided it has better use for the nearly square
kilometer of land the thing took up and replaced it with a log-periodic.

The log-periodic was several dB better, both transmit and receive, in
part because there was no longer the 50% termination resistor loss.



--
Jim Pennino

wrote in :

The log-periodic was several dB better, both transmit and receive, in
part because there was no longer the 50% termination resistor loss.


Thanks, I'll look at those a bit next time I can see well enough to read
much. Even the name is new to me right now..

What I'm wondering is shy so much current discussion of whombic antennas at
all. I try to follow the tech posts because short repeats of good info may be
my best shot at absorbing it efficiently, but I'm not sure how rhombics got
such repeated notice.

Lostgallifreyan wrote:
wrote in :

The log-periodic was several dB better, both transmit and receive, in
part because there was no longer the 50% termination resistor loss.


Thanks, I'll look at those a bit next time I can see well enough to read
much. Even the name is new to me right now..

What I'm wondering is shy so much current discussion of whombic antennas at
all. I try to follow the tech posts because short repeats of good info may be
my best shot at absorbing it efficiently, but I'm not sure how rhombics got
such repeated notice.

Someone is attempting to make some sort of point by comparing apples and
strawberries.

The rhombic was a big deal in it's day back when huge, empty areas were
readily available and better antennas had not yet been invented.


--
Jim Pennino

wrote in :

The rhombic was a big deal in it's day back when huge, empty areas were
readily available and better antennas had not yet been invented.


I like apples and strawberries, but I'll not go into it.

I had a very quick look at log-periodic antennas before I sleep. That looks
like a much more practical notion to me. I guess practical DIY might still be
limited to shorter wavelengths, but it looks like a neat, compact and solid
antenna design, ideally suited to anyone with some accurate tooling and a
need for directivity combined with a relatively broad bandwith reducing need
for adjustments. Would it be a contender against a tuned magnetic loop for a
beginner's experiment?

Lostgallifreyan wrote:
wrote in :

The rhombic was a big deal in it's day back when huge, empty areas were
readily available and better antennas had not yet been invented.


I like apples and strawberries, but I'll not go into it.

I had a very quick look at log-periodic antennas before I sleep. That looks
like a much more practical notion to me. I guess practical DIY might still be
limited to shorter wavelengths, but it looks like a neat, compact and solid
antenna design, ideally suited to anyone with some accurate tooling and a
need for directivity combined with a relatively broad bandwith reducing need
for adjustments. Would it be a contender against a tuned magnetic loop for a
beginner's experiment?

Like all things in life it is a trade off of various things.

The accuracy requirement, at HF anyway, is not that bad and there are
LOTS of plans for DIY log periodic antennas out there.

Upside: Basically frequency independant (over a range), all metal
construction, can directly match 50 Ohms, and gain can be increased
by increasing the number of elements and making it longer.

Downside: A high gain antenna can be quite large, require a lot of
expensive aluminum, be quite heavy and like any beam needs a tower
and a rotor.

Since it is truely frequency independant, for certain uses, like military
that could be operating on any frequency, it is an almost ideal solution.

For hams that are constrained to bands, something like a hex beam
might be a more economical solution.

Your call.


--
Jim Pennino