"Portable" Antennas

Started by KC9TNH, June 18, 2013, 03:08:46 pm

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Archangel320420

HAAAAAAAAAAAAAAAAAAAAAAAAAAAA  David.  Have YOU found a home here. We are all a bunch of nuts.

IZ2UUF

Quote from: Archangel320420 on September 10, 2013, 01:27:30 pm
HAAAAAAAAAAAAAAAAAAAAAAAAAAAA  David.  Have YOU found a home here. We are all a bunch of nuts.


Better not to take life too seriously!  :)

Quietus

IZ2UUF:  Thanks for sharing those pics and welcome.

Archangel320420

IZ2UUF Davide,

Is it permitted for you to milk a free grazing cow when camping/hiking in the Alps? Thanks.

Terry NN0AA

gil

Probably not, for fear of escalation...  ::)

Gil.

IZ2UUF

Quote from: Archangel320420 on September 17, 2013, 02:50:43 pm
Is it permitted for you to milk a free grazing cow when camping/hiking in the Alps? Thanks.


Hello Terry.

I don't think so. I have never taken into consideration to milk a grazing cow: probably you can do it as long as you are out of the shepherd's sight! :-)
By the way, on the Alps camping is forbidden almost everywhere: you can "emergency" camp overnight everywhere, but you have to be gone by early morning.

Davide

Lamewolf

October 05, 2013, 04:18:24 pm #51 Last Edit: October 15, 2013, 03:04:20 pm by Lamewolf
Quote from: cockpitbob on September 04, 2013, 10:57:33 pm
Quote from: gil on September 04, 2013, 10:42:56 pm
You don't need to spend that much Bob. You can get a high voltage air capacitor for about $70, and a thick 10ft coax patch cable to use for the loop. Use a toroid core for feeding, and you'll get your Alex loop for about $100. That's what I'm going to do..

Gil.
Great!  Me too.


If you are running QRP power levels, you don't need the high voltage cap.  Google the Rockloop antenna, its made of wire with a small air variable and will work several bands, and you can make it bigger for use on lower frequencies.  Just make some sort of collasible frame for it from wood or PVC pipe and you have a portable antenna that will knock down to a small package.  Good thing about magnetic loops is that they will work well even at low heights !

Lamewolf

Quote from: IZ2UUF on September 08, 2013, 07:52:55 pm
Quote from: KC9TNH on September 08, 2013, 06:34:42 pm
Welcome Davide, very interesting, all the information presented. A SOTA person I've had contacts with before swears by his telescoping jackite pole, and a dipole fed with 300-ohm twin lead. He very seldom sounds "QRP" even though he is.


I really believe that: the antennae commonly used for QRP activity are so inefficient that something as simple as a dipole gives unbelievable results. The classic 30 ft "fishing pole" antenna in 40m gain is -10 dBi or less, never mind those 5 ft "miracle" sticks.

73 de Davide IZ2UUF


There is no need to worry about RF in the shack from balanced feedline, since it is balanced, the fields in the feedline cancel each other.  Coax on the otherhand is more likely to radiate RF unless some means of choking is used to keep RF off the outside of the shield, ie: current baluns, RF choke, ferrite beads.  I call the problem of RF on coax the "3rd wire syndrome", you have the inner conductor, then the shield, and then the outside of the shield that does sometimes look like a 3rd wire to RF !

Lamewolf

Quote from: IZ2UUF on September 09, 2013, 04:56:55 pm
Quote from: cockpitbob on September 09, 2013, 10:56:13 am
- I carry no stakes, just one fishing pole;
- to hold the fishing pole, I have velctro ties in case I find a little tree or other suitable fixed structures; otherwise I use what I find, like stones;
- the setup time ranges from 10 to 15 minutes, depending on what kind of support for the fishing pole I find.


Davide


I just carry a big screwdriver that the handle will fit in the butt end of the fishing pole, stick the screwdriver in the ground, unscrew the buttcap off the pole and slide it down over the screwdriver.  Works like a charm !

IZ2UUF

October 16, 2013, 05:29:12 am #54 Last Edit: October 16, 2013, 05:32:18 am by IZ2UUF
Quote from: Lamewolf on October 10, 2013, 01:56:41 pm
There is no need to worry about RF in the shack from balanced feedline, since it is balanced, the fields in the feedline cancel each other.  Coax on the otherhand is more likely to radiate RF unless some means of choking is used to keep RF off the outside of the shield, ie: current baluns, RF choke, ferrite beads.  I call the problem of RF on coax the "3rd wire syndrome", you have the inner conductor, then the shield, and then the outside of the shield that does sometimes look like a 3rd wire to RF !


Well, actually you might still have RF in the shack even from balanced feedlines. This happens if load is not balanced: currents in the feedline would not be the same and they would not cancel. In this case, we would need a balanced tuner, i.e. a tuner able to force equal currents with 180° phase even on unbalanced loads.
This is a good reason to aim to symmetrical aerials, like the dipole I have described.
The balanced/unbalanced tuners on the market (like many MFJs) force balancing by mean of a 4:1 wideband balun: ANT->LINE->BALUN->TUNER->COAX->RIG.
The problem is that the BALUN, at that position, is working where SWR is very high, reducing its efficiency.
There are some tuners (like Double-L Networks) that are able to force equal currents by design without the balun workaround. However, using a balanced antenna, i.e. offering the same impedence on both sides (electrically symmetrical), we can use ANT->LINE->TUNER->BALUN->COAX->RIG, where the BALUN can be a simple choke. In this case, the TUNER does not need to be balanced, since currents are balanced by themselves due to the symmetrical load.
If COAX is short and RIG is not grounded, the path COAX->RIG is so short that its impedance at HF frequency is very high, so we can get rid of the BALUN. This becomes a very simple setup.

I also would like to add some calculations about efficiency of the whole system comparing a 16m long horizontal dipole fed with 20m of 450 ohm window line and a tuner and two resonant single-band dipoles in 20m and 15m fed by 20m of RG-213 without tuner, all mounted at 10m on the same ground.


  • radiation diagrams and antenna feed point calculation is done using 4NEC2;

  • feedline impedance transformation and loss over mismatched load is done using Transmission Lines Details 2.0 by AC6LA;

  • tuner dissipation is calculated using T-Network Tuner Simlator by W9CF; its calculated results match pretty closely the measurement I made myself on my tuners;



This is the situation at 14 MHz (multiband dipole is red, monoband resonant dipole is blue):



Non resonant 16m-long dipole
Impedance ad feed point: 449+j1044 
Transmission line 20m 450-ohm: loss 0.21 dB 
Impedance at tuner: 1910.240+j1477.946
Tuner loss: 0.3 dB
Total antenna system gain: 6.32-0.51 = 5.8 dBi

Resonant 14 MHz dipole
Impedance ad feed point: 73.1+j0       
Transmission line 20m RG-213: loss 0.46 dB
Total antenna system gain: 5.62-0.46 = 5.16 dBi


This is the situation at 21 MHz (multiband dipole is red, monoband resonant dipole is blue):



Non resonant 16m-long dipole
Impedance ad feed point: 499+j1534 
Transmission line 20m 450-ohm: loss 0.430 dB 
Impedance at tuner: 5057.142+j288.847
Tuner loss: 0.5
Total antenna system gain: 8.81-0.5-0.43 = 7.88 dBi

Resonant 21 MHz dipole
Impedance ad feed point: 70.7+j0       
Transmission line 20m RG-213: loss 0.544 dB
Total antenna system gain: 6.37-0.544 = 5.826 dBi

These figures seem to prove that some very common ham myths like "the ideal solution is a single-band resonant dipole, multi band dipoles are just compromises", or "a tuner will dissipate most of your power" are just... myths.
A setup made of a longer dipole, open-wire and tuner outperforms any single band tuned dipole on a frequency range of about F to 2*F, where F depends on the length of the non-resonant dipole.

73 de Davide IZ2UUF

Lamewolf

Quote from: IZ2UUF on October 16, 2013, 05:29:12 am
Quote from: Lamewolf on October 10, 2013, 01:56:41 pm
There is no need to worry about RF in the shack from balanced feedline, since it is balanced, the fields in the feedline cancel each other.  Coax on the otherhand is more likely to radiate RF unless some means of choking is used to keep RF off the outside of the shield, ie: current baluns, RF choke, ferrite beads.  I call the problem of RF on coax the "3rd wire syndrome", you have the inner conductor, then the shield, and then the outside of the shield that does sometimes look like a 3rd wire to RF !


Well, actually you might still have RF in the shack even from balanced feedlines. This happens if load is not balanced: currents in the feedline would not be the same and they would not cancel. In this case, we would need a balanced tuner, i.e. a tuner able to force equal currents with 180° phase even on unbalanced loads.
This is a good reason to aim to symmetrical aerials, like the dipole I have described.
The balanced/unbalanced tuners on the market (like many MFJs) force balancing by mean of a 4:1 wideband balun: ANT->LINE->BALUN->TUNER->COAX->RIG.
The problem is that the BALUN, at that position, is working where SWR is very high, reducing its efficiency.
There are some tuners (like Double-L Networks) that are able to force equal currents by design without the balun workaround. However, using a balanced antenna, i.e. offering the same impedence on both sides (electrically symmetrical), we can use ANT->LINE->TUNER->BALUN->COAX->RIG, where the BALUN can be a simple choke. In this case, the TUNER does not need to be balanced, since currents are balanced by themselves due to the symmetrical load.
If COAX is short and RIG is not grounded, the path COAX->RIG is so short that its impedance at HF frequency is very high, so we can get rid of the BALUN. This becomes a very simple setup.

I also would like to add some calculations about efficiency of the whole system comparing a 16m long horizontal dipole fed with 20m of 450 ohm window line and a tuner and two resonant single-band dipoles in 20m and 15m fed by 20m of RG-213 without tuner, all mounted at 10m on the same ground.


  • radiation diagrams and antenna feed point calculation is done using 4NEC2;

  • feedline impedance transformation and loss over mismatched load is done using Transmission Lines Details 2.0 by AC6LA;

  • tuner dissipation is calculated using T-Network Tuner Simlator by W9CF; its calculated results match pretty closely the measurement I made myself on my tuners;



This is the situation at 14 MHz (multiband dipole is red, monoband resonant dipole is blue):



Non resonant 16m-long dipole
Impedance ad feed point: 449+j1044 
Transmission line 20m 450-ohm: loss 0.21 dB 
Impedance at tuner: 1910.240+j1477.946
Tuner loss: 0.3 dB
Total antenna system gain: 6.32-0.51 = 5.8 dBi

Resonant 14 MHz dipole
Impedance ad feed point: 73.1+j0       
Transmission line 20m RG-213: loss 0.46 dB
Total antenna system gain: 5.62-0.46 = 5.16 dBi


This is the situation at 21 MHz (multiband dipole is red, monoband resonant dipole is blue):



Non resonant 16m-long dipole
Impedance ad feed point: 499+j1534 
Transmission line 20m 450-ohm: loss 0.430 dB 
Impedance at tuner: 5057.142+j288.847
Tuner loss: 0.5
Total antenna system gain: 8.81-0.5-0.43 = 7.88 dBi

Resonant 21 MHz dipole
Impedance ad feed point: 70.7+j0       
Transmission line 20m RG-213: loss 0.544 dB
Total antenna system gain: 6.37-0.544 = 5.826 dBi

These figures seem to prove that some very common ham myths like "the ideal solution is a single-band resonant dipole, multi band dipoles are just compromises", or "a tuner will dissipate most of your power" are just... myths.
A setup made of a longer dipole, open-wire and tuner outperforms any single band tuned dipole on a frequency range of about F to 2*F, where F depends on the length of the non-resonant dipole.

73 de Davide IZ2UUF


I agree with everything you said, but I do know that onece I switched to balanced feedline, all my RF problems ceased.  With the coax fed antennas I was using, nothing I did seemd to help at all.  I used ferrite beads on everything, 1:1 current baluns at the feedpoint of my antennas, multiple grounds rods all bonded together, nothing seemed to help.  The problem wasn't all that bad, but it was there in the form of RF on your audio reports constantly.  Then one day when experimenting with a doublet fed with balanced feedline, a friend told me to take down all my other antennas and use that one because my RF problem was gone !  I've never used coax on a doublet since !  I do use an unbalanced tuner, but I don't use the built in 4:1 balun.  I do have a 1:1 current balun right outside the shack with about 6 feet of coax entering the shack and connecting to the tuner.  The antenna is a 40 meter extended double zepp 178' long and fed in the center with 450 ohm window line about 40' long and via the tuner it will work 10 thru 160 meters.  I also have a homebrew Zmatch tuner Iuse sometimes but that requires running the balanced feedline all the way in, but either way I don't have the RF problems I had with a full coax feed.

IZ2UUF

Quote from: Lamewolf on October 16, 2013, 08:30:06 am
I agree with everything you said, but I do know that onece I switched to balanced feedline, all my RF problems ceased.  With the coax fed antennas I was using, nothing I did seemd to help at all.  I used ferrite beads on everything, 1:1 current baluns at the feedpoint of my antennas, multiple grounds rods all bonded together, nothing seemed to help.  The problem wasn't all that bad, but it was there in the form of RF on your audio reports constantly.  Then one day when experimenting with a doublet fed with balanced feedline, a friend told me to take down all my other antennas and use that one because my RF problem was gone !  I've never used coax on a doublet since !  I do use an unbalanced tuner, but I don't use the built in 4:1 balun.  I do have a 1:1 current balun right outside the shack with about 6 feet of coax entering the shack and connecting to the tuner.  The antenna is a 40 meter extended double zepp 178' long and fed in the center with 450 ohm window line about 40' long and via the tuner it will work 10 thru 160 meters.  I also have a homebrew Zmatch tuner Iuse sometimes but that requires running the balanced feedline all the way in, but either way I don't have the RF problems I had with a full coax feed.


I bet it works, you did one of the best and most efficient wideband antennae you could make!
Your setup is very smart, since you are not using the internal 4:1 balun but you placed a choke-balun between the tuner and your rig.
Also, you are feeding your doublet at its center: thanks to this, currents will be balanced enough to avoid line radiation.
However, even though there might still be some unbalance on the line due to real-world differences between the two arms, the choke-balun will stop any common mode current that could run to your rig.
Therefore, the little unbalanced currents that still might be running on the balanced line will never reach your rig, as you experienced.
At home I have the same setup you have and I'm extremely satisfied.

73 de Davide IZ2UUF

Lamewolf

Quote from: IZ2UUF on October 16, 2013, 09:05:45 am
Quote from: Lamewolf on October 16, 2013, 08:30:06 am
I agree with everything you said, but I do know that onece I switched to balanced feedline, all my RF problems ceased.  With the coax fed antennas I was using, nothing I did seemd to help at all.  I used ferrite beads on everything, 1:1 current baluns at the feedpoint of my antennas, multiple grounds rods all bonded together, nothing seemed to help.  The problem wasn't all that bad, but it was there in the form of RF on your audio reports constantly.  Then one day when experimenting with a doublet fed with balanced feedline, a friend told me to take down all my other antennas and use that one because my RF problem was gone !  I've never used coax on a doublet since !  I do use an unbalanced tuner, but I don't use the built in 4:1 balun.  I do have a 1:1 current balun right outside the shack with about 6 feet of coax entering the shack and connecting to the tuner.  The antenna is a 40 meter extended double zepp 178' long and fed in the center with 450 ohm window line about 40' long and via the tuner it will work 10 thru 160 meters.  I also have a homebrew Zmatch tuner Iuse sometimes but that requires running the balanced feedline all the way in, but either way I don't have the RF problems I had with a full coax feed.


I bet it works, you did one of the best and most efficient wideband antennae you could make!
Your setup is very smart, since you are not using the internal 4:1 balun but you placed a choke-balun between the tuner and your rig.
Also, you are feeding your doublet at its center: thanks to this, currents will be balanced enough to avoid line radiation.
However, even though there might still be some unbalance on the line due to real-world differences between the two arms, the choke-balun will stop any common mode current that could run to your rig.
Therefore, the little unbalanced currents that still might be running on the balanced line will never reach your rig, as you experienced.
At home I have the same setup you have and I'm extremely satisfied.

73 de Davide IZ2UUF


I had a 135' doublet setup the same way before I made the 40M EDZ, and when I switched to the EDZ, folks that I normally talked to on 75 meters thought I had bought an amp !  I never run more than 100 watts and even prefer QRP when on CW, but the EDZ made such a big difference in my on the air reports over the 135' doublet, I could hardly believe it !  It is a good antenna for all bands if you only have room for one antenna !

Lamewolf

You guys want a good portable antenna, try the Eagle One Vertical at www.w8afx.com Its basically a 40 meter quarter wave vertical (33 feet tall) and works great on that band without a tuner but will work other bands with a tuner.  I have one up at home with an Icom AH4 tuner at the feedpoint and it works 10 thru 80 meters via the tuner.  The good thing about the Eagle One is that it is telescopic and collapses down to 44 inchs when not in use !  The guy that makes them, Steve Sheers is a super nice guy to deal with and sells them by itself, with a tripod mount, or a ladder mount kit for RV's and motor homes.  I think he also sells a mount that goes on a trailer hitch for stationary mobile operation.  Check them ot.

Lamewolf

November 13, 2013, 07:29:17 am #59 Last Edit: November 13, 2013, 12:24:20 pm by Lamewolf
Quote from: SGO on November 13, 2013, 01:53:14 am
Quote from: Lamewolf on November 12, 2013, 11:50:07 am
I don't get the theory behind the Chameleon antenna ?  It states it has a "special matching device" but you must use a tuner.  If you must use a tuner which is a matching device, why not just use a plain whip and skip the "special matching device" which would eliminate some losses from the system ?  IN a manpack station the antenna is going to be a compromise anywaay, so why not eliminate as much loss as possible ? A 10' to 15' telescopic crappie fishing pole with a light wire hellically wound around it would be just as effective when fed by a tuner and would cost a lot less !


To understand what you can do with that product maybe you should watch their YouTube videos: http://www.youtube.com/user/ChameleonWalker/featured?view_as=public

I guess I should elaborate a little on what I mean.  What I can't figure out is why folks will spend so much money on something that really isn't all that special.  I mean $100 is a lot of money for a whip when there are alternatives out there that will work as well or even better for a lot less.  When I see and advertisement that the antenna will work all bands with a special matching device at its base, but you must still use a tuner, I tend to get leary of it.  If its has its own matching device, then why does it need a tuner ?  Eliminate the special matching device and you eliminate some losses in the system.  Since you must use a tuner anyway, depend on it for the matching instead of having double the losses of the special matching device and a tuner combined.  To me it sounds like the special matching device does no real matching in the first place.  Its probably really nothing more than a simple balun or unun of some sort and those can help sometimes if you are using an autotuner that is built into the radio that has limited matching range, but if you use a good outboard tuner that has a wide matching range, the unun or balun simply isn't needed and can even degrade your signal output.  What it basically boils down to is when using a compromise antenna such as when using a manpack station, you want to eliminate as many losses as possible.  Those whips are really nothing more than a fiberglas tube with wire inside, and I can make that myself for a lot less money using a simple telescopic fishing pole and some cheap wire.  I have 3 of them I have made, one is 10' long, one is 20' long, and the other is 31' long and they all work really well and I don't think I have $100 in all 3 of them !
And maybe join their Yahoo Group and chat with their members: http://groups.yahoo.com/group/ChameleonAntenna/

If you never tried to use one those antenna maybe you should.

SGO