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RE: How to Construct a Portable Station
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by KC8VWM on June 20, 2009
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KA4KOE:
Second thought....wind. Will a breeze knock it over? Might want to add a set of guys at 90 degrees to the wire.
Philip
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Hi Philip.
It doesn't mention this in the article however, the collapsible tripod has holes in the feet. I use 3 - 10" tent pegs to hold it securely in the ground. I had this antenna setup up during 50 MPH winds and it experienced no problems at all.
However, if the telescopic pole you are choosing goes up to the 30' level and above, then I completely agree with your recommendation to install 90 degree guys (perhaps on separate reels using parachute cord) as a matter of safety. Another idea is to build a second antenna exactly like the first one and you could have the capability to switch antenna directions AND the second antenna would also serve to secure the pole in place against high winds.
However, I never experienced any problems with high winds and this antenna arrangement. The ground anchored tripod does a real good job of taking care of that.
Hmmm... come to think of it Philip, this outfit would be perfect to use with your green military radio equipment. :)
My Best.
Charles - KC8VWM
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RE: How to Construct a Portable Station
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by K4JSR on June 20, 2009
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Charles and Philip;
Why don't both of you come to beautiful Downtown
Statham, Ga. next week and work Field Day with us.
You will recieve a warm Barrow County welcome, get
fed on Saturday night, and I will go kidnap Rich,
K7SV, and introduce you to him. Such a deal!
I'll also introduce you to W1TF and all of you can
argue into the night as to whether QRP and/or Green
radios taste great or are less filling!
73, Cal K4JSR
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RE: How to Construct a Portable Station
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by KC8VWM on June 20, 2009
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First, screw the SO239 to the outside of the end cap. That way, the PL259 will be easier to screw on tight.
Two, buy an FT114-67 ferrite core, and wind a balun inside the cap. While you might not notice any changes, you won't have to worry about common mode currents or noise.
Alan, KØBG
www.k0bg.com
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Yup, your absolutely right about the "good engineering" aspects of installing the ferrite cores.
(Didn't have them on hand at the time...:)
The SO-239 connector was installed on the inside of the 2" cap because of the "curvature" on the outside of the PVC cap. The SO-239 I was using has an outer square plate with 4 holes to secure it to the PVC. It is for this reason it doesn't sit flush with the outer curved surface. I admit, it would have been better to have chosen an different style S0-239 without the outer square plate arrangement for this project. I just used parts I already had on hand from the parts toolbox. :)
My Best,
Charles - KC8VWM
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RE: How to Construct a Portable Station
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by K0BG on June 20, 2009
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Any antenna, other than a balanced one, requires some sort of ground plane. What shape or description doesn't matter, as long as the RF current which flows through the radiating element has some way of returning to the source. In the case of a vertical, that's its radial field, however it is constructed.
Antennas like the purported "end-fed dipole" (there really isn't such a thing) don't have a way for the RF to return to the source, so it flows back down the coax in the form of common mode currents. Basically the same things happens with J-poles, and OFC fed doublets. The amount of common mode current depends on a lot of factors, mostly related to how it is erected. It is this fact, that some folks think they work okay, and others have RFI problem. And too, the level of RF is related to how severe they are. At QRP levels, you can get by with just about anything (or over look it) depending on one's view of on-air performance. It's this latter debate (argument really), that's up in the air (pun intended!).
Comet's CHP-250 isn't any different. While it also uses a 6:1 transformer to feed its radiating element, it exhibits common mode currents as well. Here too, the installation does make a difference with respect to the level of common mode current. But the real issue with most of these wonder antennas, they're all about 20 to 50 dB down from a properly designed one. As a result, unless you have another antenna to compare it to, most folks don't realize (or care) about the level of efficiency. My earlier comment about using the number of DX stations worked, is seemingly all that matters.
If you're into this category of comparison, fine and dandy. I'm not!
Alan, KØBG
www.k0bg.com
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RE: How to Construct a Portable Station
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by KC8VWM on June 20, 2009
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Charles and Philip;
Why don't both of you come to beautiful Downtown
Statham, Ga. next week and work Field Day with us.
-------
Hi Cal,
Thank you for your warm, sincere and most gracious invitation.
While we had a heck of a good time and fond memories of our previous visit with you and Philip in the past, I have to sadly decline this time around due to other pre arranged commitments.
Thank you.
Charles - KC8VWM
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How to Construct a Portable Station
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by N4NSS on June 20, 2009
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I have a source for these laundry reels. They have a "K" like mount twist instead of being threaded.
I can get them for under $2.75 each.
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RE: How to Construct a Portable Station
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by QRZDXR2 on June 20, 2009
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Charles
Well.. well... nice antenna design... except that its been done before... several times.
Even the military has one like it made by hygain back then and while they didn't use laundry reels.. they did use wire holders. Later even Collins came out with the old measuring tape reel antenna.
However, its a good stab at getting all the things in one bag. Just want to see you go from the car to the field in one trip with all this stuff.
However, when you get their what are you going to do sit on the grass with the bugs. (by the way nice looking lawn... glad to see you mowed it expecally for shooting this article.. grin... by the way also... does everyone in your neighborhood paint their house white?? geeze about the only color you have is green grass and white houses or structures..huh) LOL
However, I think I would make the changes that K0BG suggests due to his experteese and I concure with the balun idea also to improve the matching as well as the isolation of the coax to antenna.
However, after going throught your design several years ago.. I found a much easier way to get the antenna up... first build the tennis ball launcher... to get it up in the top of the trees... and if your hungry you also can pop a squirl out of the tree with it... once you have the fishing line up (you didn't consider using that for your tie offs (para cord wt. 1.8 lbs, rating 2,000 lbs fishing line wt 0.02 lbs, rating 250 lbs).. easy job to pull the antenna wire. Lay out two or three other lengths of wire on the ground... and attach it to the AH4 icom antenna tuner... and instant auto tune everything from DC to daylight antenna. Cheap, light and easy to transport too. I keep mine in two old sampson breif case's .. one for the radio and power.. the other for the AH4, antenna wire.. tennis ball shooter gizmo... spare balls.. etc. easy to tranport and gor-ella proof according to sampsons adds. light too.
However, that still leaves the .. where do you sit and operate factor. Grass is nice but cold and gets damp leaving all those nasty green stains. So what we do is take the 4x4 with the radio already mounted in the ting and about the only additional is to attach the antenna from the tree to the tip of the whip on the vehicle... the AH4 then will retune and works like gangbusters.
However, we used it that way now for several field days and always come in with nice scores around the US as well as over yonder... and when were done... can be back on the road in 5 in flat... jerk the wire down, tell the squirl off and throw it in the back.. and we're gone... easy simple and no work... and we got to sit in a nice leather comfiee seat while operating... and if it rains u only have to roll up the windows... sweet. Now one also needs susbstance. The cooler loaded with your favorite bevg, ice cold... A BBQ to cook the brocks and everything right at the back tailgate door... ahhh thats field day...
However, all this being said... ya done good on the lawn, painting the house WHITE..(no purple houses YET??) and your antenna... which, after everyone gets done here, will have it re-designed and won't look like the orginal... OH and don't even condsider getting your name associated with the commercial version. It has been proven that if you put it on the web.. and someone picks it up commercially, they won't even acknol you. Several of the others we know refuse to share with the web because of the theft of ideas without a mention of the person who made it first. (RE WA6CDE's 4BTV coax attachment plate, shown here on Eham, (still in the archives) yet a while later a manufacture came out sells it with no mention of CDE's idea.) His airstream antenna also was credited to someone else. Yet when he was down here years ago for the airstream rally, we went to see him and the antenna... to see if it would work on our airstream trailer... and it did. He gave the engineering drawings away freely to all. Several other hams at the airstream rally also took pictures of his design. Suddenly it shows up in QST as a how to article by someone else who also was in the airstream group. Go figure.
However, with all being said... ya done good and Thanks for shareing your ideas. It would be nice if instead of pictures only you had some drawings and specs if someone wanted to dup it.
Carry on... lets see some real time contact reports..life is too short for QRP.. grin.
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RE: How to Construct a Portable Station
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by NO6L on June 20, 2009
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>by N3JBH on June 20, 2009
>"...Aw i see the Maxx comm used resistors.. Well great news folks !!! now resistors and no potting gunk is used in these... toriods thermaleze wire , tefflon tubing , nylon and yes even some copper pipe. BUT not one single resistor to be found in it..."
So, tell me, how do you make a simple piece of wire sticking out the end of a coaxial cable work as an antenna without a counterpoise? You can still put all the mumbo-jumbo toroids, jigger pins, Teflon wire and capacitors in a box all you want and it still needs a counterpoise. In a nutshell, like K0BGW said, without one, all you're going to do is couple RF energy to the outside of the shield of the feed line, just like an EH or Isotron "antenna" does.
"Where's the counterpoise? The laws of physics says you need a counterpoise. I want my counterpoise."
NO6L
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RE: How to Construct a Portable Station
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by KC8VWM on June 20, 2009
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QRZDXR,
does everyone in your neighborhood paint their house white??
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Lol - That sir is the neighbors 3 car garage and 2 story workshop -behind- his house. A link to Google earth is in my QRZ profile. :)
I live in the county on a few acres of land with lots and lots of green grass. ...Not really much fun to mow actually, but it's great place to play with antenna's!
Oh, I suppose I could have posted boring technical drawings of the antenna setup as you have proposed however, I wanted to capture the essence of a field day setup with all the pretty colors only photographs could possibly capture. :)
My Best,
73 de Charles - KC8VWM
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RE: How to Construct a Portable Station
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by KG6WOU on June 20, 2009
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I like this design and keep hoping at some point to find some reels robust enough to do the job.
The tape-measure design is cool enough [and Nebraska Surplus has the original tapes available but no holders] but the way they are designed..heavy center section to be sure.
I've tried to locate cheap used fly-reels for the wire but I've yet to find a basket of them at a garage sale.
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