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eHam Forums => Antenna Restrictions => Topic started by: KD2HCU on November 26, 2022, 06:06:47 AM

Title: Sideways J shape random length antenna
Post by: KD2HCU on November 26, 2022, 06:06:47 AM
       Living in a condo I have serious antenna restriction problems.  I have a very low attic in which I placed my antenna.  I've set up a random length (about 40') in a 26' long space, which resembles a capital "J" laid on its side.  It works better than I expected in the direction of the long side (south) in about a 270 degree arc, but seems to be totally blind in the direction of the short part.  I live on Long Island and can reach Georgia and the Carolinas with ease, get the Michigan and Wisconsin area but the furthest I've gotten to the north is eastern Connecticut.  I don't know how to use modelling software and it probably doesn't work for something like this.  Any ideas how to string 40' in a 26' space without blocking out a major portion of the pattern?
Title: Re: Sideways J shape random length antenna
Post by: GEORGEMINK on November 26, 2022, 06:17:42 AM
If you have room, I would try to make a W pattern horizontally with 90 degree legs
Title: Re: Sideways J shape random length antenna
Post by: K9AO on November 26, 2022, 09:27:04 AM
Could you get a remote tuned magnetic loop up in the attic on a rotator or manually rotate it?

It's hard to figure patterns inside. You'll have wiring and other metallic and lossy material in places you can't see. Some of that might create reflections or losses.

The best thing to do is to experiment.

How are you feeding that wire?
Title: Re: Sideways J shape random length antenna
Post by: WB6BYU on November 26, 2022, 10:01:49 AM
What bands are you using?

How are you feeding it?

Are you using any sort of ground / counterpoise /
radials at the feedpoint?

What is the spacing between the short and long
sides of the J?
Title: Re: Sideways J shape random length antenna
Post by: KD2HCU on November 26, 2022, 04:20:38 PM
I appreciate all of the responses.  The height of the attic is 4' at the peak with wooden truss construction.  Plenty of electrical wires up there too.  The "W" might work if I can get far enough towards the eaves, don't think a loop with rotator would fit and wouldn't want to go up there to rotate it.  I'm feeding it with rg8x with an ugly balun choke and 3 counterpoise wires.  Gonna try shortening it to 31' and see if its been blocking itself with the short side.  So far I've been able to reach anybody I can hear and usually only run 20 to 40 watts (never over 60 yet).  I suppose I should be happy with the performance considering what it is, but as hams we always want to improve.
Title: Re: Sideways J shape random length antenna
Post by: WB6BYU on November 26, 2022, 05:51:00 PM
Better and easier than modeling software:

Generate an azimuthal map (https://ns6t.net/azimuth/azimuth.html) centered on your QTH.

Set the distance field to 3260.  That spaces the distance circles on
the map at 500 mile increments from your QTH.

Now, consider the density of hams in the arc between 340 degrees
and 200 degrees, and within 2000 miles of you.  And especially
between 30 degrees and 1800 degrees within 1000 miles.

There just aren't a lot of hams in that area.  Yes, there are a few in
W1, VE1 and VO (and FP, of course).  But generally very low
population density, ham or otherwise, in NE Canada and the
Atlantic Ocean.

Of course, it will also depend on what band you are using.
At a relatively low height, you are likely to work mostly within
1000 miles on 40m and 80m, and not less than about 500
miles or more on higher bands, depending on propagation
at the time.  If you're trying to use 20m, then you aren't
going to get much to the NE other than relatively local
E-skip.

So a number of factors will affect your ability to work
stations to the East of you, including propagation, frequency,
and time of day, but mostly there just aren't a lot of
hams in that area, and probability theory would suggest
you are much more likely to make random contacts in
other directions instead.

And that is without considering the radiation pattern of
the antenna itself.
Title: Re: Sideways J shape random length antenna
Post by: KD2HCU on November 27, 2022, 06:01:12 AM
Never considered the population of hams in New England, gotta be some up there.  I even tried reaching some that were spotted in POTA with no luck.  The dead spot seems to be from about 300 - 50 degrees (why isn't there a degrees symbol key on my keyboard) I can live with that but still gonna try messing with the antenna.  I've made several contacts in the Canadian maritime provinces and Ontario, which are beyond where I can't hit, radio propagation is a strange thing.
Title: Re: Sideways J shape random length antenna
Post by: WB6BYU on November 27, 2022, 10:55:03 AM
Years ago I was operating my QRP rig from a campground
in New Hampshire during a rainstorm.  I gave my QTH, then
as I signed over to him, one corner of my tarp came loose,
and I had to run around and tie it off before everything got
soaked.  When I finally put the headphones back on, he was
just finishing some sentence, and proceeded with the usual
exchange.  Turns out the whole time I was otherwise occupied,
he was whooping and hollering about finally working a NH
station.  I don't remember his QTH, but he was a W1 or a W2.
Overall, the number of stations in the first call area is less
than any of the other 10 districts - look at the current callsign
assignments and see the difference.  And the Maritimes aren't
very heavily populated, either.  VE2 is certainly more common.


Propagation can be quirky.  At night, you may not be able
to work stations closer than 400 miles or so on 80m.
Even during the day, 20m may not open for distances less
than 600 to 1000 miles, depending on conditions.

Those are likely to skip over much of New England and the
Maritimes, although close contacts (like CT) may be made
via other modes.

So it makes a big difference what bands you are using,
as well as the time of day and the height of your antenna.

Two tools that I like for checking propagation are VOACAP (https://www.voacap.com/hf/)
and the Australian Space Weather Forecasts (https://www.sws.bom.gov.au/Category/HF%20Systems/Online%20Tools/Prediction%20Tools/HF/HF.php?CatID=6&SecID=7&SecName=Online%20Tools&SubSecID=1&SubSecName=Prediction%20Tools&LinkName=HF), particularly
their LAMP (Local Area Mobile Prediction) charts for local
contacts out to 1000 km / 600 miles.  They don't always agree
with each other, as they make different assumptions. (VOACAP
lets you define power level, antennas, etc.)



The orientation of your antenna, and where it is fed, makes
a difference, too.  Generally, longer distance contacts will
be more difficult off the ends of the wire than off the sides,
although close contacts (on 40m and 80m when the
ionosphere is cooperative) won't show as much difference.
Title: Re: Sideways J shape random length antenna
Post by: WA3SKN on November 27, 2022, 02:56:57 PM
OK, got you in the middle of Long Island in a condo/townhouse.  The building is at a 30 degrees/210 degrees true.
Now what bands are you using and at what time of day?  Who are you trying to contact?  I assume no outside antennas, but can you hide a stealthy one?

-Mike.   
Title: Re: Sideways J shape random length antenna
Post by: KD2HCU on November 27, 2022, 03:52:15 PM
I'm mostly on 20 and 40 Meters, mostly trying to hit some POTA stations and an occasional CQ caller.  I always start out at 5 watts, and go up from there, generally if I hear someone I can reach them with no more than 60 watts (my wire is hung from wooden rafters and I'm overly cautious about generating heat).  I've gotten great responses here.  This morning I rolled up 10 ' of the curved end to see if it would help, Heard plenty but nothing in New England, was raining pretty hard so that wasn't a valid test.  I have a wire in the tree outside, but I use it with a weaker rig and a battery.  My yard is about 20x25 with tree cover over most of it, its a bit hard to throw a line straight up.  I find playing with antennas to be fun.
Title: Re: Sideways J shape random length antenna
Post by: WA3SKN on November 28, 2022, 08:54:08 AM
Trees! ???
Just shoot a wire over one of the trees.  Then pull on both ends and the wire will find a home in the branches.  End feed with a tuner working against ground.  40m and 20m should be easy enough to load.
Radiation pattern should be mostly low angle vertical polarization and good for DX.

-Mike.