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[Articles Home]  [Add Article]  

5/8 40-Meter Antenna

K0FF (K0FF) on January 24, 2010
View comments about this article!

 

KØFF Homebrew Tips

 
KØFF's 5/8 40M Transmit Antenna
 
 
Probably all hams of a certain age have dreamed about an insulated 5/8 wavelength antenna for 40 meters at one time or another.
 
My version of ON4UN's 83 foot transmit antenna is used at KØFF for 40 meters only, but his article in LOW BAND DXing
shows how to use it on other bands as well.
 
The first challenge was to decide on which base insulators to use from the various styles available,
both new and surplus
Fig. 1:
 
I chose the medium sized High Voltage Buss insulators, shown in various sizes in the above photo.
These were mounted between two 1/4" CRS steel plates that I had designed and built (one is shown in above photo),
resulting in a "sandwich" that was exceptionally strong and rated at very high voltages.
 
A"sandwich" at work. While the compression strength of the assembly is absolutely no problem, the
shear strength was unknown, so slots were engineered into the plates to accept steel pipe spacers held in place with
large bolts, used during tilt-over events.
Fig. 2:
 
A FEW DETATILS ABOUT THE BASE INSTALLATION
 
Three one foot holes for concrete were drilled into the earth with a tractor mounted post-hole digger. Only about 4 feet deep,
into these were inserted large J-bolts then filled with concrete. A form was used to keep the bolts aligned during curing.
Once prepared, a one meter diameter heavy aluminum plate was first installed, rim drilled to accept the 1/4" galvanized radial bolts.
Then on top of the J-bolt is mounted the bottom plate of the sandwich and the rest installed piece by piece. The top plate of
the sandwich holds the Rohn tiltover clamps to which the 56' tower is eventually mounted. Radials are tuned and insulated above ground their whole length, cut for 160, 80 and 40 meters since at the time I had ideas for a multiband vertical.
 
A Rohn 56' self-supporting tower was selected to use as the main antenna element with aluminum tubing gleened from various previous vertical projects. Out the top of the tower is a short 2" mast to which the top element is clamped using a typical vertical antenna mount.
 
Because the antenna is mounted near the edge of the bluff, heavy winds were anticipated. To eliminate this as a problem two levels of Dacron rope were used as guys. Guypoints were made from pieces of UNISTRUT and bolted to the tower at the joints using the regular tower bolts supplied by Rohn.
 
Fig. 3 - Guypoint hardware:
 
MATCHING to FEEDLINE
 
This antenna is one of several I made to use 75 Ohm feedline. The L-C match was worked out with the assistance of K7GCO.
 
Heavy duty parts were employed for long life, including doorknob capacitors.
Fig. 4:
 
As usual with my antenna installations, grounding and counterpoise are considered separate elements.
 
Next to the antenna I mounted a telephone pole with a big pulley at the top. With the aid of my trusty tower rope and
tractor, installation and service is a dream.
 
FINISHED ANTENNA
 
Fig. 5 My dream 40M antenna:
 
RESULTS
 
It's been up over 15 years now and I must say that I am pleased with the results. No way would I ever use a vertical antenna to receive on, but for transmitting, it is superb. Signal reports have been embarrassing actually. Once during the initial test-out, I was tuning up on SSB, and a stateside ham broke in and said" My gosh! You have the strongest signal I have ever heard on 40M". I went back to him and explained the antenna, and that I was tuning up with ONE WATT!
 
See you in the pileups,
Happy Homebrewing, Geo>KØFF

Member Comments:
This article has expired. No more comments may be added.
 
5/8 40-Meter Antenna  
by K9WJL on January 24, 2010 Mail this to a friend!
I really like reading your articles. I'd like to read about your antennas for receive someday.
Did you ever paint or galvanize the pads or enclose the matching network?
73,
Bill K9WJL
 
5/8 40-Meter Antenna  
by N2EY on January 24, 2010 Mail this to a friend!
Fascinating!

But why not some form of shunt feed?

73 de Jim, N2EY
 
RE: 5/8 40-Meter Antenna  
by K0FF on January 24, 2010 Mail this to a friend!
Thanks for your comments. Some of my receive antenna stuff is in the archives here at eHam, especially the
shielded Loops or Sloops. Also I have personally found that Beverages work fine on all bands, 40 and below. They
seem to drop off the earth at 30M for some reason.

All steel fixtures here get a coat of cold galvanizing spray, and usually a top coat of grey enamel. The cold galvanizing
works well, especially after an item has been sandblasted. Cold galvanizing comes in spray cans like paint or in paint
cans to be applied with a brush. Check your local hardware supplier or W.W. Grainger. Whenever welding is necessary,
we do it with MIG machines so that the flux is nil. Rod arc welding is had to clean up after, in terms of corrosion proofing.

One of our towers is a Rohn SSV commercial tower, with a 3N top section. At that time ( early 1990's) they did not make rotor
plates or top plates for these towers, so we built our own out of 1/2 steel. The cold galvanizing has held up well now for well over 1
5 years. The mast on that tower is 24' of heavy wall, 80,000 PSI mechanical tubing of chrome-molly. also cold galvanized.

73's
Happy Homebrewing
Geo>K0FF
 
RE: 5/8 40-Meter Antenna  
by WD8LIC on January 24, 2010 Mail this to a friend!
Very nice. Thanks for sharing!

Bob wd8lic
 
RE: 5/8 40-Meter Antenna  
by K0FF on January 24, 2010 Mail this to a friend!
Jim said: "But why not some form of shunt feed?

73 de Jim, N2EY "

Shunt feeds work extremely well too of course. The "why" part is because I always wanted to, and now had a chance to have an insulated platform for experiments.

http://www.qsl.net/k0ff/Antenna%20Projects/Station.txt

Geo>K0FF
 
5/8 40-Meter Antenna  
by W4II on January 24, 2010 Mail this to a friend!
Hey George.....

How about some info on the LC feed/matching device? I have seen your location many times driving to K0CA or K4VX QTH's. GREAT location!!

73 John W4II
 
RE: 5/8 40-Meter Antenna  
by WX7G on January 24, 2010 Mail this to a friend!
Nice antenna. Simulation shows a gain of 2.7 dB over a 1/4 wavelength vertical. This is at a take-off-angle of 10 degrees and over 'average' ground.
 
RE: 5/8 40-Meter Antenna  
by K0FF on January 24, 2010 Mail this to a friend!
John said: "Hey George.....

How about some info on the LC feed/matching device? I have seen your location many times driving to K0CA or K4VX QTH's. GREAT location!!

73 John W4II "

Hi John, this is a very radio-active part of the country, 3 stations all on or close to same road, all top of the honor roll! Glad we are spaced out a few miles apart!! Must be the good soil?? Stop by sometime or we all can do lunch.

The matching section is taken directly from Low Band DXing as far as component values, just beefed up a bit to handle power.

Have plans for a remte tuner for multiband but like so many other plans, it never happend (yet?).

Geo>K0FF
 
5/8 40-Meter Antenna  
by N0AH on January 24, 2010 Mail this to a friend!
You know Geo...it is just a matter of time before MFJ begins mass marketing your antenna now- nice article- enjoyed seeing the insulators-
 
RE: 5/8 40-Meter Antenna  
by N2EY on January 24, 2010 Mail this to a friend!
K0Ff writes: "The "why" part is because I always wanted to, and now had a chance to have an insulated platform for experiments."

Two EXCELLENT reasons! Each, by itself, is more than enough.

Thanks

73 de Jim, N2EY
 
RE: 5/8 40-Meter Antenna  
by K9MHZ on January 24, 2010 Mail this to a friend!
Very nice!

Excellent point by mentioning the compression and shear strengths of the insulators. One of the first things taught in a materials course in an engineering curriculum is that ceramics (insulators) are very good in compression (like in your design), but not as good when loaded in other axes (normal or shear stresses).

Looks like you nailed it.

Cheers,

Brad, K9MHZ
 
RE: 5/8 40-Meter Antenna  
by K5END on January 25, 2010 Mail this to a friend!
"...One of the first things taught in a materials course in an engineering curriculum..."

That reminds me of the professor in my materials course. He must've said 1,000 times, "thou shalt not put ceramics in tension." I still get a laugh when I recall that from decades ago.

 
RE: 5/8 40-Meter Antenna  
by W5WSS on January 25, 2010 Mail this to a friend!
Nice job on the design and install. I can not see the feed line well enough to determine whether or not you have it weather proofed. I can see polyethylene and I can see braid maybe you used a clear silicon treatment. If not have you done a feed line check for more than spec attenuation? Sometimes it is so gradual we do not even notice. 73
 
RE: 5/8 40-Meter Antenna  
by W7ETA on January 25, 2010 Mail this to a friend!
All of my straight keys, bugs, and paddles salute your problem solving skills. TU FB article.

73
Bob
 
RE: 5/8 40-Meter Antenna  
by K0FF on January 25, 2010 Mail this to a friend!
"Posted By W5WSS

Nice job on the design and install. I can not see the feed line well enough to determine whether or not you have it weather proofed"

Yes feedline is 75 Ohm, twin shields. One shield grounded at antenna end, both are grounded at the entrance panel.

All coax's here use self-amalgamating pure vinyl tape over the connector, topped with Scotch 33+ black tape and a final spray of clear Krylon.

At this tower, the feedline terminates in a PL-259, then a barrel connector, and a short piece of coax to the antenna feedpoint.

When going around rotors, use a similar setup, with a jumper between the fixed part of the tower and the mast. This jumper can be removed for antenna/ feedline testing, or replacement.

This form of weather sealing has served us well, yielding fresh as new looking connectors after 10 to 20 years in the weather.

Geo>KØFF
 
RE: 5/8 40-Meter Antenna  
by N2EY on January 26, 2010 Mail this to a friend!
I am reminded of two sayings that apply:

"Anything worth doing is worth overdoing."

"Because he can"

Again, a great article. Although you have Beverages, loops and such, I wonder how it works on receive during low-noise times.

Can we see more pictures?

73 de Jim, N2EY
 
RE: 5/8 40-Meter Antenna  
by K0FF on January 26, 2010 Mail this to a friend!
Jim, N2EY said:"I wonder how it works on receive during low-noise times."

I could answer that by asking, "when are the lower bands in a low noise time?"
This antenna receives just fine. The gain on transmit also applies to receive. However once you
ever use a receive antenna, you'll know why I call this and all my verticals "transmit antennas".


Geo>K0FF
 
RE: 5/8 40-Meter Antenna  
by KU7I on January 27, 2010 Mail this to a friend!
George,
What time of day are you usually on? What freq? I would love to hear this on the air.

Lane
Ku7i
 
RE: 5/8 40-Meter Antenna  
by PA7WWO on January 27, 2010 Mail this to a friend!
Hi to All

Last summer we have put up 2 portable half wave verticals for 40 mtrs. and we put them apart a half wave.
Then we started to feed these antenna's in phase or out of fase.

Feeding was done with old fasioned 600 ohm ladderline, and the fasing line between the verticals was also a half wave 600 ohm ladderline.
Switching was done by just simple plugging one vertical to the other wire of the ladder line.

We have had great fun and great reports using these verticals.

At home I use a single 1/2 wave vertical on 40 mtrs which I also use as a 1/4 wave on 80 mtrs.
It is a non guied antenna and its standing for 6 years now without any trouble.

I have made beatifull dx's with this antenna.

Details on how to make a J-antenna for 40 mtr or 20 mtrs you can find on this website.

http://blogs.hamstart.net/blog02/archives/33

You can also find the methode of fasing and feeding with ladderlines.

good luck with your 5/8 for 40 mtrs.
I ll have to do with just my half wave at home.
But I only have a small garden of only 18 x 45 ft and my shed is also in the garden so I dont have that much room to put up antenna's or towers.
That is why it is a non guied construction as I dont have the room to connect any gui wires.

73 Jos
 
RE: 5/8 40-Meter Antenna  
by KA4KOE on February 10, 2010 Mail this to a friend!
I play with a 32' military AT1011/U hitch mounted on my Tacoma. Its embarrassingly awesome in terms of radiating. We understand your reluctance to brag about your antenna, of course. I may add a couple of sections to the AT1011/U to get a full 5/8th wave on 40m.

FEELEEP
KA4KOE
 
RE: 5/8 40-Meter Antenna  
by K0FF on February 11, 2010 Mail this to a friend!
KA4KOE said:
I play with a 32' military AT1011/U hitch mounted on my Tacoma. Its embarrassingly awesome in terms of radiating.

FEELEEP
KA4KOE "

That would be a most interesting article.
Please do write it up. What do you do about the counterpoise? Just use the vehicle? Do you tune the vehicle half of the antenna? Geo>K0FF
 
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