Topband: FW: Nested Loops with one feedline results
charlie-cunningham at nc.rr.com
Mon Sep 2 19:32:52 EDT 2013
From: Charlie Cunningham [mailto:charlie-cunningham at nc.rr.com]
Sent: Monday, September 02, 2013 7:21 PM
To: 'herbs at vitelcom.net'
Subject: RE: Topband: Nested Loops with one feedline results
Well, the quad was built in "delta" fashion, and I just brought all the
delta drivers together at a common feed-point at the bottom of the driver
array. That resulted in Deltas that were somewhat reduced height for 12 and
10m. The elements do interact a bit, and I just spent a lot of time
adjusting the dimensions for gain, VSWR and a little fit for F/B. Net result
was great. I did most of that work IN EZNEC.
BTW - one "bugaboo" that you may have to contend with, is that your 160
delta will approach 2-wavelengths on 80m and can really screw up the pattern
on 80m. That was a problem for me with 20 and 10m and is not directly
related to the single feedline. The way that I solved it was to reduce t.he
dimensions of t.he 20m delta to less than 2 wavelengths on 10m, and I then
added horizontal wires at the ends of the 20m driver and reflector deltas to
bring them back to resonance. When building the antenna, I adjusted the
horizontal wires with a well calibrated Millen grid dipper that I kept an
eye on with the FT-1000MP. Usiln split bolts while tuning the elements makes
things a lot easier. Then solder them when everything is tuned up! :-)
From: Herb Schoenbohm [mailto:herbs at vitelcom.net]
Sent: Monday, September 02, 2013 7:02 PM
To: Charlie Cunningham
Subject: Re: Topband: Nested Loops with one feedline results
Charlie, Very interesting as it seems you were able to bring all 5 band
feed wires together at a common feed point via a 4:1 Current Balun. did you
you have to change any of the wire lengths to achieve the match on all five
bands of was the fomula 1005/f sufficient?
On 9/2/2013 6:48 PM, Charlie Cunningham wrote:
> Hi, Herb
> Something you might consider is feeding the paralleled loops via a 4:1
> current balun. I used this very successfully on a 2 el 5-band quad (my
> design) fed with RG-213 through a 4:1 current balun. Net result was
> that, while the VSWR wasn't 1:1 anywhere, it was below 1.6:1 across
> all 5-bands 20-10m. Worked great for me, and the antenna was a
> wonderful stellar performer! I did spend some months of modeling and
> working with interactions in EZNEC, but it was well worth it, and the
> antenna tuned up and performed just as the model predicted! A big part
> of the success was the use of the 4:1 current balun to feed the paralleled
> Charlie, K4OTV
> -----Original Message-----
> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of
> Herb Schoenbohm
> Sent: Monday, September 02, 2013 6:09 PM
> To: TopBand List
> Subject: Topband: Nested Loops with one feedline results
> 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 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
> Topband Reflector
More information about the Topband