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the antenna gods seem to hate me... 10m/20m, Inverted V, fan dipole will not work

M

mr_fx

Sr. Member
Oct 8, 2011
1,536
172
173
Kansas City
well I had so much luck last year... antennas just tuned up and worked for me...

well I built a 10m/20m fan dipole, cut the wire long (18ft per side on the 20m and 12ft on 10m)

I used 17 gauge insulated wire (copper) got the feedpoint at around 40 ft, suspended from a tree branch

at first I had a really bad slope about 45 degrees from 20m wire to 20m wire, and even worse for the 10m

for some reason the 857d seems to read a lower SWR on the tippy top upper portion of 10m... but the analyzer did not seem to agree...

well the best match I could find was around 10MHz, lol even then is was like 2.5:1

well today I talked Joe (the guy next door) and asked if I could shoot a few wires into his tree, he said sure, now I was able to broaden the angle, 120 or so for the 20m and around 90 for the 10m wire

for some reason after doing this the best match I could find was upwards of 5:1, that was doing a sweep with the analyzer from 10Mhz to 30Mhz
 

well first your lengths are way too long and some people swear that by using insulated wire will affect it so you need to make it even shorter than you think.

20 meters should be in the range of 16' 4" to 16' 9" per side
10 meters should be in the range of 7' 11" to 8' 4" per side

your 10 meter wire is roughly cut for 17m
your 20 meter wire is roughly cut for somewhere around 25m which isn't a legitimate band
 
hows your weather?

don't tell me you made the mistake of working on an antenna when the WX was nice:blink:
 
QROdx said:
well first your lengths are way too long and some people swear that by using insulated wire will affect it so you need to make it even shorter than you think.

20 meters should be in the range of 16' 4" to 16' 9" per side
10 meters should be in the range of 7' 11" to 8' 4" per side

your 10 meter wire is roughly cut for 17m
your 20 meter wire is roughly cut for somewhere around 25m which isn't a legitimate band
Click to expand...

I know all of this... I cut it long, but it SHOULD have a usable SWR SOMEWHERE... I checked it with the analyzer from 10MHz ALL the way to 30Mhz... never drops below 2.2 ANYWHERE...

The other thing that I am thinking is this... the feed point is about 35ft-40ft above the ground, BUT it is sitting 25ft-30ft above my deck (30ftx40ft) and a couple inches under that is a 30ftx40ft flat steel roof...

maybe 10m and 20m just don't play well with each other? I mean 20m 1/4 wave element would be seen and a 10m 1/2 wave element...
 
I have no idea why you are seeing the results you are seeing. And starting a -little- 'long' is a fairly good idea with wire antennas, much easier to trim length than add it. Fan dipoles do take longer to tune correctly, and there will be an affect on both antennas when one is adjusted. They are handy though, and they do work.
The metal roof, if it's something like 10 - 20 feet under the antennas (if I'm reading that right) shouldn't be a big problem. It will affect both antennas to some extent, but that affect can usually be compensated for in the tuning. It's really not something to waste a lot of worry over. Probably the biggest 'affect' will be in the resulting radiation pattern and it would be unusual if it 'skews' it enough to be noticeable.
I hope you've suspended the thing on pulleys, you'll go 'up/down' with it a number of times adjusting lengths.
Have fun.
- 'Doc
 
I don't think any amount of trimming is going to fix this problem... I mean no where does it drop below 2.2:1.

every time I tuned an antenna, even with my 2m stacked halos... EVERYTHING scaled... . if the first time I checked an antenna it was giving me a nice match of 1.2:1 @ 26.000Mhz and I wanted the match to be at 28.500Mhz then I would do this

28.500-26.000=2.5

2.5/26=9.6% so I would shorten the wire by around 9% and guess what!!! that 1.2:1 swr that I saw at 26.000Mhz was now a or near the target frequency of 28.500Mhz

But if the lowest swr seen is 2.2:1 even if I do trim the antenna to bring the match to a higher frequency then the match will still be 2.2:1, it will just be on a different frequency.... right?
 
How far apart are the ends of the dipoles? Not length but separation from each other. Many years ago I had a fan dipole consisting of five parallel wires all close spaced and only a few inches apart. I ran 10 thru 80m with it bit no WARC bands. Ot worked OK but was a real bitch to tune. I used a small manual tuner on the shack so anything under a 3:1 and I was happy.
 
1:1 current balun at the feed point or wrap an rf choke.

I have a multi band fan dipole for 80 through 17 works great.

15 meters off the third harmonic of the 40 meter leg.

If you take your time space the legs separately and use PVC at the ends to keep the wires spaced out and steady, tune the lowest band first, then work your way to the highest band.

With just a two band dipole it should be easy to tune. You do need to look at that metal roof, any thing metal will mess with an antenna.

the answer to your comment that "It should have a low vswr somewhere" shows thee is major inter action with something else besides the legs of the fan dipole.

Get a current balun at the feed point, get that antenna away from metal structures, tune it and talk on it.

I have contacts all over the world using mine, most of the time a 100 watts.

Have fun
 

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