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Author Topic: 30-40-80m dipole/inverted V  (Read 4418 times)

Posts: 2

« on: February 22, 2013, 01:43:37 PM »

Hi guys
I would like to experiment making a 30-40-80m inverted V
I have searched the web and numerous publications, but can find any construction details
I then decided to try design one myself, no luck either.
unless I am missing something (could be)
What I can't seem to to find or understand, is how to design the loading coils and wire segments in between

Can some one please direct me in the right direction


73 de KB2SSE

Posts: 1819

« Reply #1 on: February 22, 2013, 02:15:51 PM »

Have you searched for info on "trap dipoles"?  I just tried that and found some hits.  Most of the designs tend to cover bands in addition to those you mentioned.  An 80M dipole fed with open wire line and a simple tuner will work at least as well as a trapped version and is what I use for the bands you are interested in.

73, Floyd - K8AC

Posts: 17484

« Reply #2 on: February 22, 2013, 03:23:29 PM »

Analysis is not a trivial task, though easier if you have a computer modeling
program to work with.  A trap can use a range of values for L and C, and
doesn't need to be resonant on the operating frequency.  The connecting
wire lengths depend on the details of each trap.

Traps are somewhat more efficient when the traps are NOT resonant at
the operating frequency, but that means that ALL the wire lengths affect
the tuning on ALL bands, which makes it more difficult to adjust it properly.

The pragmatic approach may be better:  start with a set of traps for 30m
and 40m.  Cut a dipole for 30m and adjust the length until it is resonant.
Then add the 30m trap and some extra wire for 40m.  Adjust the end of
the wire to get the 40m resonance where you want it (the wire will be
shorter in overall length than for an unloaded 40m antenna.)  You may
need to make small changes to the 30m resonance.  Once you get it
working on both bands, then add the 40m trap on the end and enough
wire to resonate on 80m (again, it will require less total length than
an unloaded 80m dipole.  You should be able to tune up this way, which
may well be faster than trying to calculate the exact lengths.

Posts: 4314


« Reply #3 on: February 22, 2013, 06:02:55 PM »

I would like to experiment making a 30-40-80m inverted V.

How about a 148 ft. dipole fed with ~90 ft. of 450 ohm ladder-line through a 1:1 choke? It will work on 80m and 40m without a tuner but needs a tuner on 30m. You could adjust the tuner for 30m and put the tuner in bypass mode for 80m and 40m. It will also work well on 17m and 15m. The antenna is described at:

73, Cecil,

Posts: 2

« Reply #4 on: February 23, 2013, 07:43:22 AM »

Thanks to every one who replied
I knew I was on the wrong track, I did not realize that the "coils" were traps
I know how traps work, so now that I got pointed in right direction, all is well
It actually turns out, that VE6YP, the Coaxial Trap Designer, has the dimensions for what I need in the
help file of the program.

73 de KB2SSE



Posts: 9930

« Reply #5 on: February 23, 2013, 11:18:12 AM »

fan dipole

Posts: 1790

« Reply #6 on: February 23, 2013, 05:26:52 PM »

In order of ease of construction and tuning, the easiest antenna to cover that range may be a "Fan Dipole" with dipole elements for the three bands.  Second, would be something like a 130 ft. center fed "doublet" or "center fed zepp", fed with ladder line to a balanced tuner. The advantage of that antenna is you can work ALL HF bands above
80 M with that set up. (That is what I use on all bands; 128 ft. center fed system; by far the most mechanically simple/cheap and frequency flexible antenna out there.). By far, the most difficult to construct mechanically and electrically, and certainly the most time consuming to tune, would be a trap dipole with traps for 30 and 40 M. One way to make that easier might be to buy commercial traps. Mechanically, coaxial cable traps would be pretty heavy.

I am kind of biased, but I have yet to find a more effective  SIMPLE  all band antenna than the "doublet/center fed zepp" system. The only downside to this
antenna is that you need a decent tuner and you have to retune if you make large frequency changes, but you can use the antenna from 160 M (by tying the conductors together and feeding it as a random end fed wire) to 6 M or even above if you have an appropriate tuner. It is not the perfect antenna, but it is a highly efficient radiator and almost infinitely frequency flexible. A lot to like for a few bucks of wire, three insulators and some ladderline. There is a reason this antenna is still very popular and widely used after 70 years.... it is simple and it works very well.

73,  K0ZN
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