[Elecraft] Rhombic antenna "gain"

[Lyn Norstad]

While I would love to have a rhombic, or multiple rhombics, it's not a
consideration for me.  But I do have a 2 acre "semi-rural" lot, and approx.
400 x 150 feet clear space behind the house.  We have an HOA with antenna
restrictions, but I managed to get elected to the board and was subsequently
able to convince my colleagues to change the rules just a bit.

After establishing my coverage goals and analyzing different options for
best use of that space (including available supports) and my resources, I
decided on an Extended Double Zepp.  It's oriented to give me maximum gain
at 3.5 MHz in a North-South direction with NVIS properties (desired), and
maximum gain in an East-West direction on 40 meters. On 30 meters, and to a
lesser degree on 20 meters, it produces NE, SE, SW and NW lobes.  It tunes
to a very useable match on all bands, 160 thru 6 meters.

I feed it with 600 ohm True Ladder Line from a hybrid (4:1 voltage/1:1
current) balun in the attic requiring only about 20 feet of coax to the
KPA/KAT500 in the shack.

In a box outside I have a balanced line lightning arrestor, and also a heavy
duty knife switch for positive antenna grounding (I am admittedly paranoid
about lightning ...).

It theoretically produces 4.7 dbi gain on the major lobes, and serves my
purposes very well on all bands.

Prior to the HOA changes, I was limited to a G5RV Jr. in the attic.  It
worked fairly well, but nothing like this.  I still use it as a backup
during thunderstorms when the EDZ is disconnected.

Lyn, WØLEN



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic Rosenthal
Sent: Saturday, September 14, 2019 5:56 AM
To: Elecraft Reflector
Subject: Re: [Elecraft] Rhombic antenna "gain"

Just bring 600 ohm open line feedlines down from each end to a common point,
where you have a relay or two to switch the feed and the terminating
resistor. Then you can reverse it with a flip of the switch. Although
transmit gain is the same as bidirectional, you can cut the noise by 3 dB.

Victor 4X6GP 

> On 14 Sep 2019, at 2:21, Fred Jensen <k6dgw at foothill.net> wrote:
> 
> Mike:  Rhombics can be operated either terminated or unterminated.  If
unterminated, they are bi-directional with half the power in each lobe.  If
terminated, the resistor absorbs half the power in the reverse lobe.  Either
way, half your power goes the "wrong" way, either behind your desired
direction or heats a big resistor.  They have a very low radiation angle and
a fairly narrow beamwidth which is why they're flame throwers and very
common in military and commercial stations, particularly in the days of
point-to-point radio circuits.  V-beams, sometimes called Half-Rhombics are
sort of likewise only broader azimuth patterns more suitable for maritime
ship-shore telegraphy circuits.  For ham applications, Google W6AM
> 
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
> 
>> On 9/13/2019 3:24 PM, Mike Markowski wrote:
>> Can you expand on this, Ken, or if easier, a reference?  I'm curious what
tradeoffs are made.  I used a rhombic at Ft. Monmouth, NJ before the Army
base was closed in 2011, and used to boom into Europe and Russia.  It was
amazing.  I also got copies of WWII manuals on rhombic construction while
there.  You know, just in case I became wealthy with tens of acres of land.
:-)
>> 
>> 73,
>> Mike ab3ap
> 
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