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[Articles Home]  [Add Article]  

Screwdriver Antenna Use with a Motor Home

Ted (WB2LOU) on January 14, 2011
View comments about this article!

Back in my eHam.net article of February 2, 2007 titled "My Motorhome Installation of a Screwdriver Antenna," I described my project of setting up and using a ground mounted screwdriver antenna for operation while in living in my motor home.

Over the years this worked quite well. The only problem or headache was the wire radials.The wires were small diameter wires and easily broke off if someone tripped on them.

Well when AD9DP wrote the article in the November 2010 issue of QST about his portable tape measure antenna, I realized his use of metal tape measures for the vertical section as well as his radials was an excellent substitute for the wire radials on my screwdriver antenna set up. His idea is superb.

I used only 4 tape measures and at the end of each radial I have a solar power lamp so that at night people can see there is something there and in daylight the lamp marks the end so people can avoid the layout.

This combination permits me to adjust the antenna for almost a perfect SWR across the 80 to 10 meter bands. The set up meets the campground requirements and avoids wires hanging from a tree or pole whiich is not permited.

Here are 3 photos of what I did using AD9DP's idea.

Member Comments:
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Screwdriver Antenna Use with a Motor Home  
by WX7G on January 14, 2011 Mail this to a friend!
Most excellent! I'll keep your tape measure radial idea in my bag of tricks and use it some day.
 
RE: Screwdriver Antenna Use with a Motor Home  
by KG6WLS on January 14, 2011 Mail this to a friend!
Very slick idea. We'll see if it measures up to the antenna gurus. ;-)
 
Screwdriver Antenna Use with a Motor Home  
by K3GAU on January 14, 2011 Mail this to a friend!

What length tape measures did you use?
 
Screwdriver Antenna Use with a Motor Home  
by KB2DHG on January 14, 2011 Mail this to a friend!
INNOVATION, Just another part of Amateur Radio... Very nice artical... Bravo! I love to read about tips and ideas like this.
 
RE: Screwdriver Antenna Use with a Motor Home  
by W9PMZ on January 14, 2011 Mail this to a friend!
probably would work even better if you used as many radials as the antenna is tall.

73,

carl - w9pmz

 
Screwdriver Antenna Use with a Motor Home  
by KJ6BSO on January 14, 2011 Mail this to a friend!
Did you use Imperial tape measures or Metric tape measure? ;-)
 
RE: Screwdriver Antenna Use with a Motor Home  
by N8BOA on January 14, 2011 Mail this to a friend!
Looks like a little rocket ready for blast off
 
Screwdriver Antenna Use with a Motor Home  
by VE3KKQ on January 14, 2011 Mail this to a friend!
Metric tape measures are for contacts with those countries using only the metric system.
 
Screwdriver Antenna Use with a Motor Home  
by KI4ENS on January 14, 2011 Mail this to a friend!
Quick question, How are the tape measures attached to the ground plate? I can't tell in the picture. Did you drill a hole through them or clamp them? Nifty ideal.
 
Screwdriver Antenna Use with a Motor Home  
by K8QV on January 14, 2011 Mail this to a friend!
Why not just stick it on top of the motor home?
 
RE: Screwdriver Antenna Use with a Motor Home  
by WB2LOU on January 14, 2011 Mail this to a friend!
I removed the paint from the end of the tape and soldered a copper wire (#12) loop on to it. The loop is then connected to the ground plate with SS screws and wing nuts. I used a little of the anti-oxidant electrical paste to enhance the connection. Also the photo does not show that the ground plate is connected to the ground side of the antenna mount...w/o it this would not work.

The tape measures are 16 ft, but shorter tapes will work, but a few more would be required. I spent many hours tweaking the number of radial wires and lengths before actually settling on the tape measures. Four (4) 16 ft tape measures are minimum for this set up. I will be adding 2 more to improve the impedance match.

When you can work Alaska, Europe, Central Russia, or Australia on 100 watts from a motorhome with this set up, you do not need much more !!
 
RE: Screwdriver Antenna Use with a Motor Home  
by WB2LOU on January 14, 2011 Mail this to a friend!
Some have asked why not put it on the roof of the motorhome?....well the motorhome is not grounded and ( I am not antenna guru), but putting the antenna and ground plane on the roof raises the ground plane above actual ground. I think this changes the capacitive effect with the ground and this will change the impedance match dramatically.

Besides an antenna on the roof of a motorhome in Florida is a lightening rod...I do not need that!!
 
RE: Screwdriver Antenna Use with a Motor Home  
by WB2LOU on January 14, 2011 Mail this to a friend!
Some have asked why not put it on the roof of the motorhome?....well the motorhome is not grounded and ( I am not antenna guru), but putting the antenna and ground plane on the roof raises the ground plane above actual ground. I think this changes the capacitive effect with the ground and this will change the impedance match dramatically.

Besides an antenna on the roof of a motorhome in Florida is a lightening rod...I do not need that!!
 
RE: Screwdriver Antenna Use with a Motor Home  
by K0BG on January 14, 2011 Mail this to a friend!
Hum. The motor home isn't grounded. What difference does that make? The truth is, none!

If the RV is aluminum, the chances are the effective ground plane it offers is no doubt better than just four radials.

Alan, KBG
www.k0bg.com
 
RE: Screwdriver Antenna Use with a Motor Home  
by K0BG on January 14, 2011 Mail this to a friend!
One more thing. A nominal, decent quality, screwdriver antenna, will have an input impedance of about 25 ohms. That's a 2:1 SWR. If you tune it slightly off frequency, it might go down a little depending on how the SWR is measured. But if it flat, than there are additional losses, typically ground plane losses.

So the question is, what is the input impedance at resonance (X=)?
 
RE: Screwdriver Antenna Use with a Motor Home  
by KG0AQ on January 14, 2011 Mail this to a friend!
I use a predator screwdriver mounted on the hitch of my 33' 5th wheeler and it works fantastic. I use the frame of the 33' trailer for a counterpoise. A 60' wire whip into the top of an adjacent 80' oak tree doesn't hurt either. hi
 
RE: Screwdriver Antenna Use with a Motor Home  
by N8NSN on January 15, 2011 Mail this to a friend!
A question for W0BG, or others:

With the impedance mismatch seen at 25 ohms, an inductor could be placed between the base of antenna's vertical radiator and the ground plate.

A small roller inductor (about 1 inch in diameter) with 20 to 25 turns or less would work nicely to adjust out that mismatch per band, after the antenna is set to resonance.

For example: 40 meters, on my pickup truck, only requires about 7.5 turns spaced at 1/16 inch ctc of #14 bare solid copper on a 1.25 inch o.d. PVC form. This home brew, fixed-ratio shunt coil is clamped to the base, of a home brew center loaded antenna, and the frame of the truck at the point where the antenna stud is mounted.

For the article posted, on the antenna used here, a small, low-voltage motor to drive the roller inductor would be convenient for foul weather, but not essentially required. More control lines for the stepping motor introduce more "trip-hazards". So, the manual method of adjusting the roller inductor could be best. Also a set of coils could be fabricated per each band of use and mounted with banana jacks/binding posts method. These coils could be made with enameled 18 gauge wire, tightly wound (no space), on 1 inch PVC forms. Thus, requiring fewer turns, smaller coils, and more aesthetically pleasing.

What do you think?
 
RE: Screwdriver Antenna Use with a Motor Home  
by N0YXB on January 15, 2011 Mail this to a friend!
Maybe Ted doesn't want to climb on the roof every time he sets up his antenna, especially when there are inclement weather conditions. Ignore the naysayers, and thanks for sharing a solution that works for you.
 
Screwdriver Antenna Use with a Motor Home  
by N7RCF on January 15, 2011 Mail this to a friend!
I made a mount for my Butternut HF-6V vertical that attaches to the bicycle rack on the fifth wheel. The mount is well grounded to the 33 feet of steel frame as a counterpoise.
If I have the area, I also have eight 35 foot ground wires that I can lay out around the rig.
I allow them to just droop down the two feet from the feed point to the ground. This set up, with such a large antenna is of course best for longer term stays in one place like some do seasonally. The mount and antenna are broken down and stored in the basement of the fifth wheel for travel. I have had much success with this set up, and have worked lots of DX (especially digital modes) from our favorite winter campsite on the Virgin River outside Zion National Park. I DO, of course get questions about that THING on the back of my rig! One other curious comment on this set up. The truck is usually parked in front of the rig with the fifth wheel hitch in the bed nearly touching the pin on the trailer (about 6 to 8 inches). I have been in a QSO with someone when the XYL jumped in the truck and drove away. The SWR changed dramatically and I had to retune!

73 de N7RCF

Rick
 
RE: Screwdriver Antenna Use with a Motor Home  
by K0BG on January 15, 2011 Mail this to a friend!
Actually, it doesn't even take that.

A simple coil, about one inch ID, and 7 turns, will work well. All you need is an antenna analyzer to adjust it (change its overall length). Once finished, the SWR will be under 1.5:1 anywhere the antenna is resonant.

Here is something you might want to read: http://www.k0bg.com/match.html

One aspect, always overlooked, is that any antenna will work. The real issue in that statement is, what is the definition of "work"? Certainly the four radials work better than just a ground rod, or tripod, but you still end up with a lot of common mode current. That too should be choked off, but few do. Aside from RF in the shack, if RF can get out, it can get in too, which effects the receive as well.

We need to get past the "it works" stage, and start asking ourselves what we can do to improve the overall efficiency. Sometimes that is very difficult, and sometimes it is easy. The real knowledge is knowing which is which.

Alan, KBG
www.k0bg.com
 
RE: Screwdriver Antenna Use with a Motor Home  
by K0BG on January 15, 2011 Mail this to a friend!
Go to my web site, and pull up the Photo Gallery. Look in the OTR & RV album. Then look for kb1jtb.

Although this one is a manual fold over, there are other ways. Go to the Other Installs album, and search for kg0sh

Note the linear actuator used to raise and lower the antenna.

As my father used to tell me all of the time, necessity is the mother of invention!

Alan, KBG
www.k0bg.com
 
RE: Screwdriver Antenna Use with a Motor Home  
by GM0GTU on January 16, 2011 Mail this to a friend!
Wow! It looks like KB1JTB has covered the whole of his Motor home roof with aluminium tread plate. That must have taken some time, and cost a fair bit of money. I dread to think what that would cost in the UK at today's aluminium prices. Still, It's food for thought, and could be a solution for my motor home.
I can see that I'll have to pay regular visits to the local scrap merchants. I suppose I could start with one sheet, and keep adding to it as more become available.

Best regards, Stewart GM0GTU
 
RE: Screwdriver Antenna Use with a Motor Home  
by WB2LOU on January 16, 2011 Mail this to a friend!
For N8NSN and others the antenna is a Tarheel screwdriver antenna...it is motorized and controlled from inside the motor home. Read my previous article published in 2007. I use ferrite chokes on the control line and a coaxial choke on the coax feed line at the motorhome. It probably needs to be at the antenna base instead. However I cannot detect ant RF getting back into motor home.

I probably do not get a perfect match, but it is close. Is it set at the most efficient point? Probably not.

Does it allow me to contact friends on a regular schedule and talk with other Hams in the world? YOU BET it does!

At 75 I do not climb onto the roof as often as in the past, so this arrangement gets it done for me.

As a side note I carry with me a wire ground plane antenna for each band 40 through 10 and a 1/2 wave 40 meter antenna made with lamp cord wire...these are used depending on location, ease of set up, and weather conditions. They all work !!

73, WB2LOU
 
Screwdriver Antenna Use with a Motor Home  
by VK6ZRY on January 17, 2011 Mail this to a friend!
Sheer genius Ted, you realise the antenna on the Oscar 1 satellite was a steel measuring tape too, good old Aussie idea.
The cover slid back and out popped the antenna.
Your idea is on the the same par.
They are so cheap (Walmart I guess) and so easy to unlock and roll up.
Hope to spot you on Wspr soon, 30M is usually the best to start with and use Atomic time to less than 1 second.
Most of use use Dimension 4 (free) to keep your PC on time.
 
RE: Screwdriver Antenna Use with a Motor Home  
by VK6ZRY on January 17, 2011 Mail this to a friend!
BTW Ted on Wspr you will only need 5 Watts to reach me, maybe less on 30m, a mate in Germany gets here on 1 watt everyday.
 
RE: Screwdriver Antenna Use with a Motor Home  
by W6MQI on January 17, 2011 Mail this to a friend!
N0XYB
<<<Maybe Ted doesn't want to climb on the roof every time he sets up his antenna, especially when there are inclement weather conditions. Ignore the naysayers, and thanks for sharing a solution that works for you.>>>

Not to mention possibly causing leaks in the roof it's not built like the roof of your house that can be walked on without fear of causing a roof leak. Ted good job keep experimenting.

73
 
Screwdriver Antenna Use with a Motor Home  
by N6CTW on January 17, 2011 Mail this to a friend!
If I was to do this economically, I would buy one 100 foot tape measure and two 100 foot of low voltage malibu lamp cord that can be split in half. I would then cut the radials for the ground mounted antenna to the lowest possible frequency operation, leaving extra that can be trimmed, using the tape measure to measure with. Then attach the wire to the radial plate and measure response of the screwdriver antenna at that time at the lowest frequency. If the screwdriver is used for a higher frequency, then the excess wire can be rolled up to a ball of each ground radial, to meet the require amount that is needed. At that point, I would mark each wire with a small piece of duct tape to determine the amount of ground mount radials for each band, is needed for the next time that I was going to set up a ground mounted screwdiver verticial antenna. Wire is cheap (two rolls @ 100' is +/- $40.00 total), four tape measures cost more (+/- $100.00 total)!

Cliff, N6CTW
 
RE: Screwdriver Antenna Use with a Motor Home  
by K7GLM on January 18, 2011 Mail this to a friend!
I guess I go for quantity over length for this exercise, but I certainly wouldn't spend $100 on tape measures.

Northern Industrial (through Sears web site) sells a 12 pack of 25 foot tapes for $29.99. For $2.50 each, I can lay down a field of 12 one inch wide, 25 foot long, non-resonant ground radials and get on the air.
 
RE: Screwdriver Antenna Use with a Motor Home  
by K7GLM on January 18, 2011 Mail this to a friend!
My bad - they no longer offer this set. But they do have 12 thirty three footers for $49.99.
 
RE: Screwdriver Antenna Use with a Motor Home  
by KE5YRF on January 20, 2011 Mail this to a friend!
Great idea! I use a Tarheel 200 mounted to the ladder on the rear of my motor home with the ladder grounded to the frame with 1 inch braid and it works well on all except 80 meters. The SWR on 80 is a little high but nothing that my tuner can't handle. The antenna is mounted with just the whip extending above the roof line and that seems to keep rf out of the house. I don't travel down the road with it back there as the whip would whack every bridge and underpass that I go under. I used a Comet CHA 250 for a couple of years and it also worked well. Just a pain in some campgrounds.

73
Doc
 
Screwdriver Antenna Use with a Motor Home  
by KD7DCR on February 3, 2011 Mail this to a friend!
Nice idea...and, yes, there are lots of sources for cheap tape measures out there...Tool Shack and swap meets come to mind first...maybe even Ebay, eh?..

The issue of RF "inside the house" is one that I have seen noted before...some have mentioned frying parts of their monitor system, heater control board, and one said something about the voltage regulator on their genset...all were more than $200 to fix once fried... How do you guys make sure that this is the case, kept out..?? Ground everything?? Use a ground rod to the frame?? Keep the radiator above the coach roof or over xxx feet from the coach?...Does power level enter into this, say 1-KW from solid state???

Just some of the questions that came to mind while reading it..

73' to all
 
Screwdriver Antenna Use with a Motor Home  
by KF7OM on February 4, 2011 Mail this to a friend!
I have for years used a screwdriver antenna mounted to the roof ladder on the rear end of my RV and bonded the ladder to the frame, I have no need for radials as the frame becomes the GP,it has never failed to give me a flat SWR with a coupler. works well without the coupler too.The antenna is motor driven off the back of my astron PS.73,John KF7OM
 
RE: Screwdriver Antenna Use with a Motor Home  
by W5AOX on February 18, 2011 Mail this to a friend!
Many if not most motorhomes made in the last 20 years have little if any metal in the structure, unfortunately.
Mine has a metal bead running around the vinyl siding edges but getting my screwdriver to load was unpredictable and difficult until I added "radials" consisting of small guage insulated wire radiating out from the feedpoint of the screwdriver. I used 4 and ran them out from the screwdriver feedpoint as far as the shell of the RV would allow. This made the interior of the RV relatively RF-free (no more weird tinglies when keying the mic) and finding resonance very easy. I've also added aluminum plates underneath my VHF and UHF verticals to make them work better as well.
 
RE: Screwdriver Antenna Use with a Motor Home  
by KE4D on February 18, 2011 Mail this to a friend!
I run across this issue all of the time. Even a fiberglass skinned RV has a nice metal chassis and frame. All of this is bonded together and makes an excellent counterpoise for an antenna. I've been using screwdriver antennas on the top of my ladder for years. However, my current antenna is an Eagle One 33 foot collapsible pole with a flex weave conductor inside it and tuned with a tuner at the base of the antenna. It's a good quarter wave on 40 so it also loads nicely on 15 even without a tuner. One again, the metal frame and chassis of my motorhome serves as a nice counterpoise.
When I am plugged in at a campground the coach is grounded through the ac plug but when boon docked it's not
As for being a lightning rod in FL that is simply paranoia. A screwdriver isn't any more of a lightning rod than your batwing tv antenna. Bring it down in a storm. Mine sits on a tip over device. It rides horizontally when I am moving or during bad weather.
 
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