Try a loop yagi=

"David" wrote in message
...
Hi,

I am looking for recommendation for a design of antenna to operate
in the band 915-928 MHz.

The desired response is omni-directional with gain greater than or equal
to a 1/2 wave dipole, something that does not require a ground plane
and is reasonably straight forward to manufacture in-house.

So far I am considering a 1/2 wave vertical dipole with feed through lower
element, J-Pole and Collinear.

Thanks in advance for any ideas or link to a web site that might have some
homebrew versions I could replicate and try.


--

Kind Regards

David Huisman

Howard, W3CQH wrote:
"Try a loop yagi."

Construction details are given for 1296 MHz Loop Yagis in my 19th
edition of the ARRL Antenna book and easily scaled to 915 MHz.

Best regards, Richard Harrison, KB5WZI

Howard,

How do you get an onmi-directional pattern from this antenna ?

The other issue is that at 921MHz, the unit is almost 1m long (too big
to mount in our indoor applications)

Howard W3CQH wrote:
Try a loop yagi=

"David" wrote in message
...

Hi,

I am looking for recommendation for a design of antenna to operate
in the band 915-928 MHz.

The desired response is omni-directional with gain greater than or equal
to a 1/2 wave dipole, something that does not require a ground plane
and is reasonably straight forward to manufacture in-house.

So far I am considering a 1/2 wave vertical dipole with feed through lower
element, J-Pole and Collinear.

Thanks in advance for any ideas or link to a web site that might have some
homebrew versions I could replicate and try.


--

Kind Regards

David Huisman




--

Kind Regards

David Huisman
General Manager
-----------------------------------------------------------------------
ORBIT COMMUNICATIONS Pty Ltd - Wireless Solutions that Work
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A.C.N. 107 441 869


Website : http://www.orbitcoms.com
PO Box 4474 Lakehaven
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Mobile: 61-413-715-986

David weote:
"How do you get an omni-directional pattern from this antenna?"

In a point to multipoint system, only the central station needs an omni
antenna.

One orderly radio data acquisition system operates half-duplex. Only one
station at a time transmits, and then only when called upon to do so.

A radio master interrogates remote stations within its reach, addressing
them by name, rhen listens for their response. Only a single radio
frequency is needed as remote stations don`t initiate transmissions
until callef upon. In this master-slave relationship, there is no
competition within the system for radio time.

The radio master can conveniently use an omnidirectional antenna as it
communicates with slaves on various azimuths. The slaves only
communicate with the master, even to communicate with each other. The
slaves each have a directional antenna aimed at the master.

A directional antenna improves signal to noise ratio when transmitting
and when receiving. Great gain and directionality, though desirable,
may be necessary only when very low transmitter power must be used..

The long-boom directional loop array may have a gain of 20 dB. But, a
3-element Yagi can give a 5 dBd gain which may be plenty. This gain is
almost equivalent to cutting the path length by half (6 dB).

The Yagi is close-spaced. With only 3 elements it is small and simple to
build.

Normal narrow-band receivers are very sensitive so that very weak
signals are sufficient if noise and interference are not severe. Higher
gain antennas can be used as needed at remote sites on a case by case
basis.

I built such a system decades ago and it is still in use.

Best regards, Richard Harrison, KB5WZI