Portable antenna suggestions for forthcoming QCX mini


Ted 2E0THH
 

I built my original QCX as a shack rig, so to that extent I have a home built ZM antenna matching unit constantly employed, actually I have never operated a transmitter without an AMU.

It looks like Father Christmas (AKA XYL) is going to bless me with the QCX mini for external ops, but would love to avoid lugging an AMU along if I can.

Could any of you lovely folk who operate externally recommend an antenna (probably 40m but might yet be 20m)  that has an acceptable SWR (without an AMU) and I could trust not to fry the finals, if such exists?  

73s Ted
2E0THH


Jim Allyn - N7JA
 

A plain old dipole works well.  Impedance is around 70 ohms, closer to 50 ohms in inverted vee format.


Daniel Conklin
 

I use an end fed half wave on 20 meters with a QRPguys mini tuner.
--
73, Dan - W2DLC


John AE5X
 

I'm a fan of end-feds for portable ops - they can be installed vertically, horizontally or as inverted V's depending on how many supports (trees?) are available and what polarization you want.
--
John AE5X
https://ae5x.blogspot.com


VE7VXO
 

Well if you don't want any tuner I agree with the inv-vee dipole suggestion.  The end fed half wave is tempting for the simplicity of hanging a single wire and feeding at the low end but I have found that with just a fixed match like an auto transformer that variations in the setup ie vegetation, different ground, different routing or length of feedline, can result in significantly different impedance.  If your rig has a rather fragile output you would want a small tuner which you said you wanted to avoid.  Having said this I did discuss this with a chap who lives in Ariziona and with the consistently poor ground and lack of vegetation out that way he didn't have any issues with variation of his EFHW from one setup to another.  So it depends I guess.

Joe


Mark Garrisi
 

I use a Slinky with a 20’ crappie pole vertically. Adding a 9:1 unun allows me to tune my QCX 40 meter with very good results. Tuner and ground wire accompanying the setup.

Mark N8IAJ


Curt wb8yyy
 

Ted

I also suggest EFHW. Of course look at qrpguys for ideas, but shipping may be crazy expensive.  these things can be homebrewed. I found a nice website from down under with clear instructions on building the matching transformer, and adding a coil to enhance lining up resonances on multiple bands. A single band version for 20 or 40m etc should be easy to craft.

I am told the zm2 style may not be able to match an exact half wave, but make the wire slightly longer or shorter. But it will need a ground counterpoise. Efhw is plug and play once optimized.

73 curt


Mike Besemer - WM4B
 

Anyone familiar with the MFJ1982?  A friend of mine uses one at home and I’m thinking the 40-meter version would work well in the pines in our Georgia campgrounds.

 

Mike

WM4B

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of wb8yyy via groups.io
Sent: Friday, November 13, 2020 9:31 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Portable antenna suggestions for forthcoming QCX mini

 

Ted

I also suggest EFHW. Of course look at qrpguys for ideas, but shipping may be crazy expensive.  these things can be homebrewed. I found a nice website from down under with clear instructions on building the matching transformer, and adding a coil to enhance lining up resonances on multiple bands. A single band version for 20 or 40m etc should be easy to craft.

I am told the zm2 style may not be able to match an exact half wave, but make the wire slightly longer or shorter. But it will need a ground counterpoise. Efhw is plug and play once optimized.

73 curt


jjpurdum
 

Mike:

Al and I both use the MyAntenna 80-10M EFHW and have for about 5 years and we are both happy with it. The quality is first rate and it has survived many a storm...better than the tree that holds it.

Jack, W8TEE

On Friday, November 13, 2020, 9:38:46 PM EST, Mike Besemer - WM4B <mwbesemer@...> wrote:


Anyone familiar with the MFJ1982?  A friend of mine uses one at home and I’m thinking the 40-meter version would work well in the pines in our Georgia campgrounds.

 

Mike

WM4B

 

From: QRPLabs@groups.io [mailto:QRPLabs@groups.io] On Behalf Of wb8yyy via groups.io
Sent: Friday, November 13, 2020 9:31 PM
To: QRPLabs@groups.io
Subject: Re: [QRPLabs] Portable antenna suggestions for forthcoming QCX mini

 

Ted

I also suggest EFHW. Of course look at qrpguys for ideas, but shipping may be crazy expensive.  these things can be homebrewed. I found a nice website from down under with clear instructions on building the matching transformer, and adding a coil to enhance lining up resonances on multiple bands. A single band version for 20 or 40m etc should be easy to craft.

I am told the zm2 style may not be able to match an exact half wave, but make the wire slightly longer or shorter. But it will need a ground counterpoise. Efhw is plug and play once optimized.

73 curt


W5EGA@...
 

Gil (the radio prepper) on YouTube has a nice video on the mini end fed half wave antenna. 

VK2PRC on YouTube has a variant of the end fed half wave antenna that he uses “pedestrian portable.”

Both videos give good clear instructions on how to build. 

But if you really want extreme portable check out K6ARK Portable Radio and his extremely small end fed half wave built on a BNC connector! 


Peter GM0EUL
 

Hi Ted
Another vote here for an end fed half wave with an impedance transformer, or the simplest single band option is a quarter wave vertical with counterpoise.  Dipoles are great but a bit harder to deploy in the wild because you need both ends and the middle up high.  All are very easy to make but if you want any help I'm also in the UK so just message me, I make all my own antennas and its very quick and easy if you have everything you need at hand.

Cheers
Peter GM0EUL


Richard - N1RBD
 

On Sat, Nov 14, 2020 at 03:01 AM, Peter GM0EUL wrote:
Dipoles are great but a bit harder to deploy in the wild because you need both ends and the middle up high.  
I run a 20/30/40 linked dipole with the ends only 5ft off ground level and have worked ZL land with 20w.  


Ted 2E0THH
 

Huge thanks to everyone that chimed in on this.

I think for me, EFHW is the way to go. I looked at the QRPGuys Portable No Tune End Fed Half Wave Antenna, One of the locations I will be operating is in Wales and has a HUGE conifer out the back so I think knocking up something like this will be perfect.

73s Ted
2E0THH


Torbjorn Skauli
 

For my pocket-portable QCX 20, I use a plain wire dipole, shown packed here. I have checked it with a nanoVNA in various odd configurations, and it provides a decent SWR. The center is simply a BNC female connector of the type with four screw holes (visible in the picture) which are used for strain relief. For transport, it is wound on a piece of foam plate, together with two lengths of string, which are often needed to hang the antenna from trees or buildings or whatever, and 4 meters of coax. Just before I took this picture today, one half of the antenna was suspended as an "inverted vertical" from the ski jump here, loaded by the pinecone shown. Add a fishing rod, and it becomes a pretty good vertical antenna even in the absence of a ski jump, with the ground half as counterpoise. A balun is not needed, because the coax is nonresonant and the QCX in the plastic enclosure presents a negligible stray capacitance. I thought this would be my temporary solution until I got a better antenna, but this simple thing has served me well for a long time.

Torbjorn, LA4ZCA


Arv Evans <arvid.evans@...>
 

Peter GM0EUL

What inductance, turns, and impedance transformation are you using for each band?
EFHW sounds good but using small (low cost) toroids seems limiting.  Can the 
transformer be built on a plastic tube (solenoid style air core) to support higher power?  
If so, what inductance and turns ratio would be necessary for low loss and wide bandwidth?

Arv
_._


On Sat, Nov 14, 2020 at 1:02 AM Peter GM0EUL <gm0eul@...> wrote:
Hi Ted
Another vote here for an end fed half wave with an impedance transformer, or the simplest single band option is a quarter wave vertical with counterpoise.  Dipoles are great but a bit harder to deploy in the wild because you need both ends and the middle up high.  All are very easy to make but if you want any help I'm also in the UK so just message me, I make all my own antennas and its very quick and easy if you have everything you need at hand.

Cheers
Peter GM0EUL


Peter GM0EUL
 

Hi Arv
Mine are all 49:1 impedance transformers regardless of the band.  Built according to Steve Ellington N4LQ.  The basic design is this: and Steve has some great videos including this https://www.youtube.com/watch?v=4ceZNjM-7g4


Bob KB1TEK
 

My junk box has yielded some T80-2 toroids. 

Do we think these will work well for such a transformer?

Most folks seem to use -43s  

73,
Bob


Dave VE3GSO
 

The Type 2 powdered iron toroids are more suited to the inductor in a resonant circuit.  They don’t have the permeability for an effective transformer. That is why we use ferrite cores like Type 43 or 61, much higher permeability.

Dave

On Nov 15, 2020, at 09:39, Bob KB1TEK <bob@...> wrote:

My junk box has yielded some T80-2 toroids. 

Do we think these will work well for such a transformer?

Most folks seem to use -43s  

73,
Bob


Arv Evans <arvid.evans@...>
 

Peter

Yes, most people use toroid cores.  My concern, and question, was about the 
possibility of making an air-core balun (more accurately probably a transformer)
for raising 50 ohm antenna feedline to match the much higher impedance of an 
EFHW wire.  Toroid based transformers are compact and not prohibitively 
expensive, but the cost and potential power loss from core heating could be 
less if the core was air (or plastic) and if a solenoid form, construction might be 
easier.

This method works well, but does require a high voltage variable capacitor 
to bring the antenna 
to resonance.



I have used this method at 7 MHz with the transformer wound on 3/4 inch PVC pipe.
I have not tried it as an un-tuned design without the capacitor.  I see a few posts 
saying that EFHW antennas need to be tuned (cut to frequency) but others seem 
to be using them as un-tuned systems.  Which way is proper, or are both ways 
equally effective?

Arv
_._


On Sat, Nov 14, 2020 at 6:15 PM Peter GM0EUL <gm0eul@...> wrote:
Hi Arv
Mine are all 49:1 impedance transformers regardless of the band.  Built according to Steve Ellington N4LQ.  The basic design is this: and Steve has some great videos including this https://www.youtube.com/watch?v=4ceZNjM-7g4


VE7VXO
 

A simple L-network can be very low loss when matching 50 ohms to several K-ohms so long as a good Q air variable cap is used and has the advantage of being adjustable for variations due to surroundings affecting the antenna during different deployments.  The original PAR end feds used a fixed L-network with high Q fixed capacitance.if I am not mistaken

---------- Original Message ----------
From: Arv Evans <arvid.evans@...>
Date: November 15, 2020 at 2:54 PM

Peter

Yes, most people use toroid cores. My concern, and question, was about the
possibility of making an air-core balun (more accurately probably a transformer)
for raising 50 ohm antenna feedline to match the much higher impedance of an
EFHW wire. Toroid based transformers are compact and not prohibitively
expensive, but the cost and potential power loss from core heating could be
less if the core was air (or plastic) and if a solenoid form, construction might be
easier.

This method works well, but does require a high voltage variable capacitor
to bring the antenna
to resonance.



I have used this method at 7 MHz with the transformer wound on 3/4 inch PVC pipe.
I have not tried it as an un-tuned design without the capacitor. I see a few posts
saying that EFHW antennas need to be tuned (cut to frequency) but others seem
to be using them as un-tuned systems. Which way is proper, or are both ways
equally effective?

Arv
_._

On Sat, Nov 14, 2020 at 6:15 PM Peter GM0EUL < gm0eul@...> wrote:
Hi Arv
Mine are all 49:1 impedance transformers regardless of the band. Built according to Steve Ellington N4LQ. The basic design is this: and Steve has some great videos including this https://www.youtube.com/watch?v=4ceZNjM-7g4