Best Practices for an EFRW Setup

[KO4RSJ]

I'm a fairly new Ham and only been at QRP portable HF operations for a few months. My kit consists of a FX-4CR transceiver, ATU-10 tuner, Tufteln 35 foot End-Fed-Random-Wire (EFRW) antenna, and 25 foot of RG-316 coax. The EFRW antenna has a built in 9:1 transformer and a 17 foot counterpoise. Considering my inexperience the kit has worked well. I've made lots of contacts and learned a bunch from the excellent QRPer community. I've setup the antenna system in dozens of different configurations and often wondered if there is a preferred way to arrange the different elements. I realize there are MANY variables that influence the success of a particular setup. But, is there a perfect way to setup the system?

If you had clean slate to work with and no limitations in an area, how would you arrange the different elements of an 35 foot EFRW setup?
1. Reference the radiator: How high and in what configuration (vertical, sloped, or horizontal) would you deploy the antenna? Would you prefer to have the feed end of the radiator at ground level (from a sloped or vertical deployment) to facilitate connections to the counterpoise and coax?
2. Reference the counterpoise: What is the best way to deploy the counterpoise in relation to the radiator? If the radiator is vertical, what's the best way to arrange the counterpoise? If the radiator is horizontal or sloped, should the counterpoise be oriented perpendicular or parallel to the radiator? Should the counterpoise be on the ground or in the air?
3. Reference the coax: What is the best way to deploy the coax in relation to the radiator and counterpoise?
4. Reference radiation pattern: Assuming your "best" chance for contacts is within 1500 miles to the north and south of your location, how would you orient the antenna system?
5. Is there anything else a new guy needs to know about deploying a QRP EFRW system?

To a new guy it seems like the deployment options are endless. But, I'll stop here and see how things progress. Thanks much for help!

[Andrew (grayhat)]

did you already see this ?

viewtopic.php?t=19

and then, try making your radiator longer, use this

https://udel.edu/~mm/ham/randomWire/

as a reference and try to find a longer, yet manageable lenght, next, if going "mobile" (i.e. POTA) use a telescoping rod and try to setup your radiator as inverted V or inverted L, and to conclude, also use a common mode choke (17 turns of coax around a #43 toroid will do just fine)

[KO4RSJ]

Thanks Andrew,

Yes, I've looked through that thread and learned much from it. I also understand the advantages of a longer radiator. However, the advantages of a 35 foot EFRW for my circumstances are many. My deployments, here in Virginia, are mostly under a forest canopy and if I tried to use a ~80 foot radiator it would be a tangled mess. As you pointed out a longer radiator (while theoretically superior) is just not "manageable" in many portable circumstances.

Thanks also for the info about the common mode choke. I have one and deployed my setup with and without the choke. So far, I don't notice any advantage to using the choke at QRP levels. Again, that may be due to my total inexperience and lack of correct deployment.

The best practices that I'm after apply particularly to my setup with a 35 foot EFRW and a 17 foot counterpoise. My questions/concerns may be splitting hairs and there may be no "best" way to deploy my setup. If that's the case, then I'm most happy to continue trying different setups depending on the cards that are dealt that day.

Thanks again for the help!

[Andrew (grayhat)]

Mike, for portable use, you may try going up to 40 or 60ft and still have a manageable antenna, if using an arborist line or a telescoping rod, you may then set it up as an inverted L (ok almost L that is ), just keep the feedpoint at (say) 3ft from ground or the like, the counterpoise can be laid out on ground, as for the choke it's useful to ensure your RF will be radiated by the wire and not by the coax (shield), then willing to measure its effect you may just use an "RF ammeter"

http://www.ifwtech.co.uk/g3sek/clamp-on/clamp-on.htm

to measure the amount of current flowing on the coax shield with and without the choke, not just that, by sliding the meter clamp along the coax you can find a current node (min current), that's the spot where a choke will have max effect on the given band

[Brian - K3ES]

Hi Mike,

The Tufteln 9:1 with 35 ft radiator is one of two antennas that live in my KX2 field kit. The other is a Packtenna 9:1 with a 71 ft radiator. I can tell you about my personal experience, but I claim no special knowledge. For context, I use this equipment for POTA activations, and I nearly always operate 5 watts CW. I live in northwest PA, where trees are almost always available for antenna deployment, and a miniature arborist kit also lives in my pack.

I use the longer antenna whenever possible, because it seems to yield more contacts (this is obviously very subjective). It is almost always set as an inverted V, up 20 to 35 ft at the apex. I have never used a counterpoise other than my 15 ft RG316 feedline. It tunes easily on any band from 80m to 10m (the KX2 tuner would tune the proverbial wet noodle).

I use the Tufteln for restricted space deployments. If I can get a good throw with my arborist line, and catch a high branch on a tree, I pull the radiator straight up, through the lower branches of the tree. Ideally, I leave the balun just a couple of feet off the ground, and stretch out the counterpoise in a convenient direction, and the feedline toward my operating position. I often use this setup when activating from a parking lot with overhanging trees. I've also deployed the Tufteln as a high-angle sloper when only lower trees were available. I know it tunes well (and I have contacts) from 60m to 10m, but I have not yet attempted 80m.

I generally let the trees and terrain dictate how I deploy my antennas, and the Tufteln is not an exception. I've not been unsuccessful with this method, and some of my activations have exceeded all my expectations.

Final note, I have, but do not carry or use a common mode choke for QRP activations. I've tried it, but it hasn't made a noticeable difference, so I take a pass on the extra weight and complexity.

Best 73 de Brian - K3ES

[KO4RSJ]

Andrew...thanks for the info on the "RF ammeter" and ways to objectively measure choke effectiveness on the coax shield. My experiences so far are entirely subjective and liable to much variation/error. I'll definitely keep this info in mind as I try to be more objective in judging different antenna deployments.

Brian...it sounds like we have very similar experiences with the 35 foot Tufteln EFRW. Of course that is probably due to the fact that I've learned most everything I know about portable QRP operations from K4SWL and other QRPers like yourself at QRPer.com. Yes, the BIG advantage of the 35 foot radiator is in restricted space deployments. And like you, using the 35 foot Tufteln has exceeded my (and K4SWL in several of his videos) expectations many times. My FX-4CR/ATU-10 combination has nowhere near the capability of the KX2. But like your kit, mine easily tunes 80m to 6m and makes many 5W CW contacts. Having the flexibility to change bands quickly and the ease of setup/take down a "short" EFRW makes me smile and motivates a lazy person like me to do more deployments. I like using simple things to solve complex challenges.

Here's a situation I've had a few times in the past month that led to my initial post. It's similar to this post from VE6Lk at https://qrper.com/2023/05/the-joy-of-a-low-slung-wire/ . I was in a situation with very restricted space for any kind of vertical deployment. So, I just strung the 35 foot radiator between 2 trees parallel to the ground about 6 foot high. I then ran the 17 foot counterpoise perpendicular to the radiator as a sloper to the ground. I did not use a common mode choke on the feed line. From what little I know about antenna theory this should have been a very compromised deployment. Yet, it still exceeded expectations and I made many CW and SSB contacts. There's too much "magic" in this QRP world for a simple operator like myself to fully grasp.

Thanks for helping me to understand the magic!

[Andrew (grayhat)]

Andrew...thanks for the info on the "RF ammeter" and ways to objectively measure choke effectiveness on the coax shield. My experiences so far are entirely subjective and liable to much variation/error. I'll definitely keep this info in mind as I try to be more objective in judging different antenna deployments.

Mike, regarding the choke... having common mode currents along the coax feedline means that your coax will act as an active part of the antenna (radiator), this in turn means that your coax will receive RF and, in TX, radiate it; now while the first issue (RX) can be ignored in SOTA/POTA since local QRM sources are (almost) absent it isn't the case in other setups where the coax will pick up whatever noise is radiated by local sources, be those light dimmers, motors, switching PSUs and then more, as for TX, using QRP power the amount of RF is so low to be often unnoticeable (no RF "bites" or the like), yet the coax isn't exactly a good radiator also since it's usually laid out on ground, so one may prefer pushing the few RF from the transmitter into the real radiator (the antenna) so I believe it's better setting up a choke after the 9:1 transformer

As for the "best" setup, the "random" wire is... random ok, not so for the length since we know we need to avoid resonance, but a random wire may be laid out as the environment allows, this means that it may even be a "zig zag" but in general laying it out as a straight line even sloping, as an inverted L or as an inverted V will be the most used setup, then, willing to have an idea of the radiation pattern for a given layout (and terrain type !) you may just pick a copy of 4NEC2 https://www.qsl.net/4nec2/ (free), model the antenna in the desired layout and run the simulation to have an idea of what to expect

HTH

[KO4RSJ]

Andrew...great (and very useful) explanation on uses of the common mode choke. Question to make sure I'm understanding your correctly: when you say "...I believe it's better setting up a choke after the 9:1 transformer." I take this to mean that the choke goes on the end of the coax (feed line) just before it connects to the transformer/radiator. Is this correct?

I'll definitely pickup a copy of 4NEC2 and add that to my tool box as I try to make sense of all this antenna magic.

[Andrew (grayhat)]

Andrew...great (and very useful) explanation on uses of the common mode choke. Question to make sure I'm understanding your correctly: when you say "...I believe it's better setting up a choke after the 9:1 transformer." I take this to mean that the choke goes on the end of the coax (feed line) just before it connects to the transformer/radiator. Is this correct?

I'll definitely pickup a copy of 4NEC2 and add that to my tool box as I try to make sense of all this antenna magic.

Yes, what I mean is that the "sequence" should be the following

antenna wire -- 9:1 transformer -- choke -- coax -- trx
counterpoise ----------^

as for placing the choke, it may be right after the 9:1 or placed at some spot along the coax or even near the trx, even if placing it right after the 9:1 is usually a good setup, as for 4NEC2, don't be fooled, sure maybe the learning curve isn't exactly flat, but I think it is really a useful tool just to make an example, I quickly defined a simple model for your EFRW with a 35ft radiator and a 17ft counterpoise, I placed the feedpoint at about 3ft from ground and the endpoint at about 19ft, while the counterpoise wire just drops down and runs on ground, the NEC model for such an antenna is the following

Code: Select all

' file comments
CM efrw.nec - simple random wire antenna model
CE

' base symbols
SY freq=14.175                          ' test frequency
SY leng=10.668                          ' radiator wire length
SY cpse=5.1816                          ' counterpoise length
SY wire=0.00075                         ' wires radius
SY hfed=1                               ' feedpoint height
SY hend=6                               ' endpoint height
SY segl=51                              ' segs for long wires
SY segm=21                              ' segs for mid sized wires
SY segs=5                               ' segs for short wires

' pythagorean formula
SY sidA=abs(hend-hfed)                  ' vertical side of triangle
SY sidB=sqr((leng^2)-(sidA^2))          ' horizontal side of triangle

' counterpoise calculations
SY spcr=(wire*3.5)                      ' ground spacing (NEC needs it)
SY hlow=spcr                            ' low point of counterpoise
SY lenv=(hfed-hlow)                     ' vertical counterpoise len
SY lenh=(cpse-lenv)                     ' horizontal counterpoise len

' feedpoint 
SY fwir=1                               ' feepoint wire #                   
SY fseg=1                               ' feedpoint segment #

' radiator wire geometry (wire# segments x1/y1/z1 x2/y2/z2 radius)
GW  1 segl    0    0    hfed    sidB    0    hend wire

' counterpoise wire
GW 10 segm    0    0    hfed       0    0    hlow wire
GW 11 segm    0    0    hlow    lenh    0    hlow wire

' end of geometry and ground parameters
GE  1
GN  2  0  0  0  13  0.005

' wires loading (copper)
LD  5   0  0  0  58000000

' enable extended kernel for FP calculations
EK

' place the feedpoint
EX  0 fwir fseg 0 1 0 0

' initial test frequency
FR  0  1  0  0  freq  0

' end of model
EN

and then, loading the above in 4NEC2 and running it as is, results in something like the following

[KO4RSJ]

Andrew...that post really got me thinking! I've got some questions/comments.

1. You said, ..."that the sequence should be the following: antenna wire -- 9:1 transformer -- choke -- coax -- trx -- counterpoise --" That's somewhat different than what I've been using. The Tufteln EFRW has the counterpoise incorporated at the feed point (pictures here https://www.tufteln.net/listing/1226227 ... -long-wire) to make the following sequence: antenna wire -- 9:1 transformer -- counterpoise (I assume connected to the antenna wire side of the BNC connector) -- choke -- coax -- tuner -- trx. I have no idea if my sequence would change any of your assumptions, but it is different. Comments?

2. Why have the radiator feed point 3 foot above ground and not at ground level?

3. I'll need to do some study/research on the 4NEC2 models before I can really understand what they're telling me. Right now it's like a dog watching TV.