The 18/24 is not a good analogy, because those bands
are not octave spaced. My modelling indicated that
you need to open up the lower frequency antenna at
two places, 180 degrees opposed, in order for it not
to affect the higher frequency antenna. Also, the
openings should be such that the remaining wires
are cross polarized to the higher frequency antenna.
Rick N6RK
On 9/2/2013 3:09 PM, Herb Schoenbohm wrote:
Several replies to my inquiry on having a closed 80 meter inverted delta
loop inside a 160 meter delta loop brought me some nice replies. So I
decided to build one for 18Mhz and 24Mhz with the feed going to the
outside Delta loop hoping this would properly allow dual band operation
with a single feed. The inside 24 Mhz delta was closed and hung inside a
the fed 18 Mhz antenna. The results showed that it had no impact on the
18 Mhz antenna but the VSWR on 24.9 was unusable. Then I decided to
open the 24 Mhz Delta and connect the two wires to the 18 Mhz feed and
now have both bands working with a VSRW below 1:2 to 1 on either band.
The feed-line for the antenna is RG-213 with a 1/4 wave piece of RG-11
cut for 18 Mhz. I am surprised that the 1/4 wave matching piece did not
seem to impact the antenna on 24.9 at all.
I will now proceed to build an 80 meter full wave delta inside my 160
meter one and rely on the simulation on 18/24 Mhz to get a good match. I
trust it will work although the ground proximity might have some impact
on everything.
Thanks for the replies on this.
Herb Schoenbohm, KV4FZ
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