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Author Topic: rain gutter antennas  (Read 7839 times)
K8RBV
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Posts: 11




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« on: August 08, 2014, 07:01:46 PM »

The best choice for me to operate on 40 meter QRP (5 watts) CW may turn out to be an existing rain gutter downspout.  I know, something of a compromise, but I'm willing to give it a try, at least.  Just gonna' run a wire to the downspout and a wire to a ground rod.

Any thoughts on the best tuner for such an antenna?  I'm using an MFJ-9040 rig, but will purchase an appropriate tuner.

I"ve read a lot, but would welcome thinking about this "plan."

Thanks,

Bob

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G4AON
Member

Posts: 529




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« Reply #1 on: August 09, 2014, 12:24:08 AM »

There will be significant losses with just using a ground rod. It will work better if you can run two elevated radials around 32' long. Or several buried radials around 22'.

Depending on the materials in your house, there maybe a lot of your RF absorbed in the building and also lost by being induced in house wiring.

I once ran an inverted L antenna up a house wall to a fishing pole on a balcony, then horizontally down the garden. I used a bunch of elevated radials running along the house wall. The results with a K1 on the patio table were mediocre. I did work a few stations but not many.

The inverted L was quickly replaced by a ground plane on the balcony with world wide results.

You can see the patio and balcony at my EA5 QTH (with fishing pole ground plane) on my QRZ page.

I didn't need to be stealthy, but I got much better results with the antenna out and in the clear. Perhaps you could use a temporary fishing pole with a wire up it, that is removed when not in use. It won't look too much like an antenna...

To see how far you are getting out, check the reverse beacon network   http://www.reversebeacon.net/dxsd1/dxsd1.php?f=0&c=YOUR_CALL&t=dx replace YOUR_CALL by your call and send a short test message such as VVV DE K8RBV K8RBV in a minute you will see the results.

73 Dave
ps forgot to add, if you use an ATU there will be some loss associated with it. It's much better if you can use a resonant antenna that doesn't need an ATU. Saves a few dollars too...
« Last Edit: August 09, 2014, 12:29:37 AM by G4AON » Logged
WB0FDJ
Member

Posts: 143




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« Reply #2 on: August 10, 2014, 10:55:39 AM »

Bob

Over the years I've run across several hams who were using rain gutters for antennas. Nearly all of them were doing so out of necessity. They were also all QRO. Back when I was in college I worked a guy at the University of Oklahoma who was loading the screen in his dorm window. Just about everything with metal has been tried at least once I'd guess.

Dave's comments are right on. FWIW: if I had to use a rain gutter running QRP I would make this as efficient as possible. That would entail using radials at the base, the more the better. Something to match impedance at the point where the transmission line hooks up to the rain gutter, would reduce coax losses. That said, have at it! Back in my novice days we used things for antennas that I would be embarrassed to talk about now. It was a great learning experience.

Doc WB0FDJ
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WB6BYU
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Posts: 13248




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« Reply #3 on: August 12, 2014, 04:48:19 PM »

1) Make sure all the downspouts and rain gutters are aluminum rather than vinyl.  (If the latter,
you can run a wire inside them, though putting it under the eaves will be less effected by rain.)

2) Make sure that all the downspouts and rain gutters are well bonded together - don't assume
that any joints will make good electrical contact.  A couple stainless steel sheet metal screws
in each joint are usually a good start, along with some Ox-Gard or No-Al-Ox to keep the joints
from corroding.

3) Sometimes there may be portions of the rain gutter / downspout system that you don't
want included in the antenna - in that case, use some vinyl gutter / downspout material to
insulate it.

4) If your downspouts go up to the second story and around part of the roof, that should work
reasonably well.  Generally the longer and higher the better, but it is possible to have it too long
and/or too many pieces running in different directions.

5) A single ground rod may work somewhat if it is right at the base of the antenna (though it
also has to be bonded back to your electric system ground with #6 wire for safety) but they aren't
really good for RF grounds.  Better would be some number of ground radial wires, even if you
can't make them all long or cover all directions.  At least run some wires along the sides of
the house where possible.  (Radials are a complicated topic.)

6) As long as you have at least 40' of rain gutter / downspout in the system, you should be able
to match it on 40m using an "L" network of 1 coil and 1 variable capacitor, either home made or
commercial.  The tuner should be mounted as close to the base of the antenna as possible, which
makes it inconvenient to adjust it from the shack unless you use a remote autotuner.

But if you are only trying to cover 40m, then you don't need to readjust it frequently.  I've used
fixed-tuned networks:  a adjust a tap on the coil and a variable capacitor for a match, then put
a cover over it to keep the rain off and leave it alone.  While you can do this with a commerical
tuner, that seems a bit of a waste, so I make my own using a homebrew coil and a variable capacitor
from a hamfest (possibly one that requires a screwdriver to adjust:  they are often cheap because
they aren't as convenient to use for most applications.)  It takes some trial and error to find the
right combination for a good match (though an SWR analzyer can allow you to calculate good
starting points) but once it is set it doesn't require any further attention.
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KC2UGV
Member

Posts: 441




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« Reply #4 on: August 13, 2014, 02:14:06 PM »

The best choice for me to operate on 40 meter QRP (5 watts) CW may turn out to be an existing rain gutter downspout.  I know, something of a compromise, but I'm willing to give it a try, at least.  Just gonna' run a wire to the downspout and a wire to a ground rod.

Any thoughts on the best tuner for such an antenna?  I'm using an MFJ-9040 rig, but will purchase an appropriate tuner.

I"ve read a lot, but would welcome thinking about this "plan."

Thanks,

Bob



Instead of the gutter, I would run wire under the eaves/gutter.  You're QRP already, and I would think there'd be WAAY to many variables to want to deal with.

At least with the wire, you'll know what to cut to tune.  I would also try to beg/borrow an antenna analyzer, and make sure it's tuned to your desired "watering hole", and let the tuner take care of allowing you to work the entire band.
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ZENKI
Member

Posts: 935




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« Reply #5 on: August 15, 2014, 03:59:28 AM »

Any antenna should be designed with a the question of how much gain it will have between the angles of 1 and say 20 degrees. If local communication is the only purpose then the same question should be asked about the gain at higher angles. Many hams only think about just getting the antenna up even if its  just a piece of wire stapled to the house gutter without asking this question.

If you ask this question you can find antennas like shortened verticals and magnetic loops  mounted vertical or horizontal can outperform many sneaky wire antennas. You need to learn to design antennas that plug the holes in your radiation pattern and make sure you antenna is delivering gain at the appropriate takeoff angles. In many cases hams  are installing antennas that are no more effective than laying a piece of wire on the ground because  they not asking what power they are radiating at various takeoff angles. Do more research/modelling and design any hidden antennas with gain at the appropriate takeoff angles.

KM5KG wrote a very good article  on how he installed vertical and horizontal antennas inside his roof while at the same time considering his radiation pattern for dx work. It was published in one of the antenna books. You might consider reading that article to understand more broadly what I am saying.

I once lived in an apartment in NY during a work assignment and I  had very good results with  short verticals and horizontal shortened loaded antennas. My success was playing the takeoff angle. Once settled i moved just to get access to a rooftop and used the same simple antennas. Moving away from the building metal shadow gained me 20db with a regular sched into Europe using the same shortened antennas. You have to play the gain game and takeoff angle  game with a lot of seriousness. At the end of the day  thats what counts not just putting up any antenna just for the sake of it without an design objective which seems to be the objective of many hams these days.
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K8RBV
Member

Posts: 11




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« Reply #6 on: August 15, 2014, 12:10:56 PM »

Wow.  Thanks to all for great information!

I may reconsider the rain gutter.  Back to the drawing board to find a way to put a basic dipole up somewhere.

Bob
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KL7CW
Member

Posts: 71




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« Reply #7 on: August 16, 2014, 11:41:33 AM »

Bob,
  Much good advise was posted.  Since we are hams it is OK to simply try something like a rain gutter and see how it works.  That being said, I have found modeling programs very useful and fun to use, and some models have evolved into very useful antennas which I built and used.  My "HAM" experience over 60 years has shown me that height above ground and buildings with stone walls or metal roofs and siding is often worth many dB (10 dB, 20 dB ??).  Professionally I do not like "rules of thumb",  However I have found that a 1/2 wave dipole can sometimes be shortened up to ABOUT 50 % and with reasonably designed loading coils about half way out each leg may have a loss of only a very few dB's. Dipoles (including inverted V's) shorter than this tend to suffer from greatly increased losses partly due to the loading coil, but also the low antenna Z mismatch to the coax, and greatly decreased bandwidth.  A shortened 1/4 wave vertical antenna can be reasonably effective, but this is only true if you install a very good buried radial system (lots of wire), or above ground resonate radials, AND if the vertical is reasonably in the clear. A 40 meter resonate dipole (horizontal or inverted V) is about 66 feet long.  If you need to shorten it to something like 40 feet it might be within a very few dB's of a full size dipole.  If the dipole is in the attic or under the eves it will probably work, but possibly (probably) have high receive noise from the house electronics.  If the same dipole is moved as little as 5 or 10 feet away from or above the house you could easily gain 10db or possibly much more in signal strength and possibly significantly lower receive noise.  I helped a friend install an stealth antenna under the eaves of his house.  Performance was poor, but he did make contacts.  A year later we moved the antenna up to perhaps 5 or 10 feet above his roofline.  Performance was MUCH improved for local and DX.....my very uneducated guess was 10 to 30 dB better (I know anecdotal studies are considered worthless).  A few years later we moved it way up in the trees.....I know he was a very happy camper....sorry no solid data or studies.  I have used compromised and stealth antennas and even made some good QSO's with an attic dipole on 20 meters, and ever made some 1 watt QSO's with a rain gutter antenna when visiting a friends house.  I suspect that most of these compromises cost me at least several S units.....but I still had fun.  Probably the rain gutter antenna is the worse choice but give it a try...nothing to lose.
        Rick   KL7CW   Palmer, Alaska
PS....  linear loaded shortened elements are NOT a magic solution...and may or may not outperform coil loading.  End fed half wave antennas are a good option that is favored by some QRP operators.  There are some issues with this concept, especially when running high power, such as RF in the shack, and very high voltages (many Kv !!) in the matching network or sometimes (yuk) transformer.
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QRP4U2
Member

Posts: 115




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« Reply #8 on: Yesterday at 10:58:51 PM »

WB6BYU has some good points regarding bonding of metal gutter joints.

When I ran QRP I used the MFJ-16010 tuner and the gutter as an Inverted-L antenna.

Out of the MFJ-16010 I ran the outer shield of the coax to a 4-foot ground rod about 6" away from the bottom of the downspout.

The inner conductor of the coax was connected to the downspout about 3 feet above ground, departing from the coax to the downspout at about a 60 degree angle.

Not super efficient, but it worked well on 40 and 20 meters.



Phil
« Last Edit: Yesterday at 11:03:02 PM by QRP4U2 » Logged

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