Dual Rhombic
 

Pierre Desjardins wrote:

I read somewhere that the dual rhombic could give a gain of almost 27
db using these dimension for 144,2 mHz:

L1- 29.5 ft, L2- 50.67 ft, X- 52.2 degrees, Y- 37.7 degrees, R1/2 660
ohms noninductive, Ht: 12.29 ft, Elevation angle: 7.5 degrees, Vertical
beamwidth: 5.5 degrees and Horizontal beamwidth: 8.5 degrees.

Has anyone ever verified this? Here, using simulation with EZNEC+, I
get about 15 dBi in free space and much lower on real ground. Am I
missing something?

No - it was a complete mistake.

First it was an optimistic estimate from pre-computer days. Then too
many different people each added another 6dB for ground gain.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

First it was an optimistic estimate from pre-computer days. Then too
many different people each added another 6dB for ground gain.

LaPorte was an eternal optimist. That's French isn't it?

W4ZCB

W4ZCB wrote:
"LaPorte was an eternal optimist. That`s French isn`t it?"

Edmund A. Laport was Chief Engineer of RCA International Division Radio
Corporaation of America, and is the author of "Radio Antenna
Engineering".

On page 336 of "Radio Antenna Engineering" Ed gives the gain of a
two-layer tiered rhombic as 14.7 dBd.

On page 528 of Arnold B. Bailey`s "TV and Other Receiving Antennas" is
given the gain of a single-layer "horizontal" rhombic in free-space
which has a dide length of about 3.7 wavelengths. It has a gain of about
14.5 dBd.

I`ve used Laport`s criteria in rhombic design and been satisfied.

Best regards, Richard Harrison, KB5WZI

'tis possible that it could have that kind of gain, as the reference
point (compared to Dipole (dBD), Isotropic (dBI), or WET NOODLE dB(?))
was neglected in the gain statement! In fact might be even better than
27 dB (?) when compared with a wet noodle, but that has no bearing on
any credible gain! That ANY antenna would have a gain of some 400
TIMES a dipole, or even an isotropic (Point source) would take up
considerable acreage at 2 meters! A typical moonbounce station uses
about 20 dBD gain , and these are multiple yagi antennas.
see: http://www.bigskyspaces.com/w7gj/longyagi.htm for a 19 dBD gain
2 meter yagi, and note the length! (98-1/2 feet long!)
and also look for VE7BQH - These guys have verifiable antenna gains
and know their stuff! when ANY antenna claims more than 10-11 dB I
gain ,be very suspicious of the claims, also, make sure to see WHAT
that gain is compared (referenced) against! This is at least one of the
reasons that the ARRL is loath to allow gain claims by advertizer,
unless they have been verified by independant sources. Jim NN7K

Pierre Desjardins wrote:
Hi to all

I read somewhere that the dual rhombic could give a gain of almost 27
db using these dimension for 144,2 mHz:

L1- 29.5 ft, L2- 50.67 ft, X- 52.2 degrees, Y- 37.7 degrees, R1/2 660
ohms noninductive, Ht: 12.29 ft, Elevation angle: 7.5 degrees,
Vertical beamwidth: 5.5 degrees and Horizontal beamwidth: 8.5 degrees.

Has anyone ever verified this? Here, using simulation with EZNEC+, I
get about 15 dBi in free space and much lower on real ground. Am I
missing something?

Thanks for your answers

73 de Pierre VE2PID

"Jim - NN7K" wrote in message
...
'tis possible that it could have that kind of gain, as the reference
point (compared to Dipole (dBD), Isotropic (dBI), or WET NOODLE dB(?))

THATS IT! the ultimate reference. I hereby dub that measurement the dBwn
which will from now on be used to get the best gain figures for advertising
in anything except QST.

"Pierre Desjardins" wrote in message
...
Hi to all

I read somewhere that the dual rhombic could give a gain of almost 27
db using these dimension for 144,2 mHz:

Nowhere near 27 dB.


L1- 29.5 ft, L2- 50.67 ft, X- 52.2 degrees, Y- 37.7 degrees, R1/2 660
ohms noninductive, Ht: 12.29 ft, Elevation angle: 7.5 degrees,
Vertical beamwidth: 5.5 degrees and Horizontal beamwidth: 8.5 degrees.
We did once erect exactly the same antenna. It was about 1 S unit worse than
2x 17 elements F9FT yagi, tested on RX only and for

1 hour when we hastily dismantled it due the snow blizzard :(. OTOH, -1 S
unit on 34 el yagi is nod bad for piece(s) of wire...


Has anyone ever verified this? Here, using simulation with EZNEC+, I
get about 15 dBi in free space and much lower on real ground. Am I
missing something?

This is about right. My single rhombic for 1296 MHz got pretty much the
same gain and radiation pattern as simulated in NEC2.


Thanks for your answers

73 de Pierre VE2PID

GL de Mario 9A4DE