End fed wire feed line length

[K8JFG]

I've been working with end-fed "random" wires as quick and easy antennas for transmit and receive while traveling. I'm seeing some conflicting information about critical design parameters. Lots of talk about the lengths of the wire to avoid on the various bands, but not much about feed-line length. As I understand it, the outer surface of the shield on the feed-line coax serves as a counterpoise. So what is the design issue? I've heard everything from "as long as you can make it" to "at least 25 feet" to "it doesn't matter, just make sure to use a proper choke to avoid common mode". Any thoughts or observations from folks about the proper setup for a quick end-fed wire antenna?

 

[prcguy]

I despise non resonant end feds using a 9:1 but since they are non resonant and the feedline is part of the antenna try using the closest "magic" non resonant antenna wire length for the feedline length and always use a good ferrite common mode choke. When you get tired of all the compromises we can then talk about a resonant end fed half wave.

 

[mass-man]

or just say no to the 9:1 balun/matching thingy and a hunk of wire and go resonant EFHW! I've been relegated to modest antennas most of my 50+year ham life but have found the EFHW to be a good performer for me and my antenna garden{not enuf room for a farm}

 

[vagrant]

An experienced member on these forums advised and kindly provided me with most of the material to make an End Fed antenna that works great while traveling. While I use it for QRP, an improved core transformer can handle more watts if you prefer. The parts and instructions are easy to find if you want to build it yourself.

- 49:1 transformer (The watts you intend to use will guide the core needed if you plan to build or buy)
- 20 meters of 22 gauge teflon wire. This length handles 40, 20, 15 and 10 meters (four bands) without the need of a tuner.
- I use 25 feet of LMR-240UF coaxial cable with this 49:1 transformer. About two or three feet from the radio I use a 1:1 choke. The choke I have is some store bought low power choke and then a two foot patch cable to the radio. One could easily create an RF choke using a #31 ferrite core with six or eight turns of the coax, or six to eight #31 mix beads on the coax. Just place this choke two to three feet from the radio.

I have used this with 50' of LMR-240UF coax as well and did not notice an issue. One could use different coax. I am just a fan of the LMR-240UF which is stranded versus LMR-240 which is a solid core. The difference is flexibility. Anyways, sometimes I operated close to the 49:1 transformer and the coax was just plopped on the ground, or extended out to reach my tent/vehicle/table further away.

* I definitely do not use random wire lengths for transmitting. Random lengths are friendly for SWL's using a 9:1 transformer to try and tame it for receiving.

Antennas for QRP Operation

Am getting back into QRP after a 40 year hiatus. Back then sunspot #'s were higher hi hi. Right now the antenna at the shack is a 31' vertical, ground mounted, 50 buried radials, about 280' ASL. Going to see how that works but was wondering what antennas others use for QRP operation. Yes I...

forums.radioreference.com

 

[RadioDXfun]

Being a static mobile / portable station myself and doing things the difficult way. I made myself 3 efhw's with croc clips on so I can run 10/12/15/17/20 - I run them all vertical with 100w and wound my own transformers for them.

The beauty of this is get a very nice low angle radiation pattern on all bands as the antenna's are mono band cut. Perfect for dx which is my bag. The higher the freq the more gain I get. On 10m band fed at 13m agl I modelled 3.0dBi gain at 5 degrees. And no nulls of significance up to 15 degrees where almost all DX lives on 10m.That is pretty impressive DX stats for a piece of wire. These even slightly beat my DIY 5/8 wave ground mount verticals. I suggest this if you can be bothered with the effort involved switching bands. I cannot think of a portable wire antenna to beat them.I cannot personally accept the higher band patterns when using them multi band (vertical at least not sure about horizontal or sloper)...too easy to lose DX. There can be 10dB less gain at low angles on higher bands. (For example 10m band using a 10m bit of wire for 20m)

Each has a 0.05 long CP.......at 100w with either 10 or 20m of high quality coax I have no observable CMC issues..I do not use a choke.

 

[K8JFG]

Thanks for the replies - definitely have given me some ideas to think about and work on. I typically run barefoot and looking for wire antenna solutions that are easy to use. I don't mind a tuning issue between bands - though the holy grail would be one that handles all well. I'm finding myself mostly on 20m and 40m, and my long wires both resonate well on both. But thanks everyone for the ideas.

 

[RadioDXfun]

If you have a little counterpoise on the transformer I am not convinced that CMC is high enough on the coax to cause any problems on a mono band cut with 100W. As such coax length should be ... just as long as you need it. As I gather most CMC rears its ugly head when the EFHW's are used multiband and with more power than 100W.

On 20m I have made contact into Nevada and Arizona around 15:00-16:00 UK local time in SFI of about 110, 100W barefoot. From the UK it is very easy when the 20m is open to hit Canada and the East coast/ SE USA. And slowly given the conditions on the day as people in the USA awake I penetrate further and further into the mid USA and then if really lucky get over to the Western states. So for me it is great fun getting into the Western states as a challenge as they are far from a daily given right now (last 6 months anyway).

I speak into Asia, Australia, NZ and S. and Central America, USA with regularity on 20/17. I do benefit from a low noise QTH and direct views to the horizon which helps a lot noise generally S0/S1 flickering on a vertical out in the sticks.

Good luck with it. I recommend an elevated vertical for the long haul DX on 20m band. (if you can deal with a monster size fibre glass pole). A 10m long EFHW on 20m band fed at 8m above ground works dx very nicely and I have settled on this is my main antenna. (having no radials compared to a ground mount 5/8 wave is a big bonus, they used to take me 20 mins to lay down 30 - though the 5/8 surely works nicely as well)

Of course horizontal you will experience less noise in an urban environment. Work out what you need most and take the least compromised approach that you can deal with.

 

[K8JFG]

If you have a little counterpoise on the transformer I am not convinced that CMC is high enough on the coax to cause any problems on a mono band cut with 100W. As such coax length should be ... just as long as you need it. As I gather most CMC rears its ugly head when the EFHW's are used multiband and with more power than 100W.

On 20m I have made contact into Nevada and Arizona around 15:00-16:00 UK local time in SFI of about 110, 100W barefoot. From the UK it is very easy when the 20m is open to hit Canada and the East coast/ SE USA. And slowly given the conditions on the day as people in the USA awake I penetrate further and further into the mid USA and then if really lucky get over to the Western states. So for me it is great fun getting into the Western states as a challenge as they are far from a daily given right now (last 6 months anyway).

I speak into Asia, Australia, NZ and S. and Central America, USA with regularity on 20/17. I do benefit from a low noise QTH and direct views to the horizon which helps a lot noise generally S0/S1 flickering on a vertical out in the sticks.

Good luck with it. I recommend an elevated vertical for the long haul DX on 20m band. (if you can deal with a monster size fibre glass pole). A 10m long EFHW on 20m band fed at 8m above ground works dx very nicely and I have settled on this is my main antenna. (having no radials compared to a ground mount 5/8 wave is a big bonus, they used to take me 20 mins to lay down 30 - though the 5/8 surely works nicely as well)

Of course horizontal you will experience less noise in an urban environment. Work out what you need most and take the least compromised approach that you can deal with.

Thanks - right now I've got a ~38 meter wire ~7.5 meters off the ground (actually slopes from just over 7 to just under 8), because it's strung from tower to tree it's got ~31 meters of feedline. I've also got ~10m strung from shack to tower at ~6 meters, it has ~2.5 meters of feedline. Both are working great at the home QTH for both 20 and 40, though I'm not in a very good location. I'm just working on something portable I can keep in my go-box for field use.

 

[K6GBW]

I've used a simple 29' 18AWG wire to a small 9:1 unun and 25' of RG8X as a portable antenna. I've used it very successfully on 40 and 20 as well as the higher bands. It will radiate on 80 but its kind of a joke. This set up is only for lightweight portable use. Since you can fit a 3 meter (124 feet) of wire I'd recommend an EFHW with a 49:1 unun as your go to antenna and save the short wires and 9:1 for portable only.

 

[jaymot]

Is RF in the shack an issue at 100W PEP SSB (barefoot HF rig, I don't plan to use a linear amplifier in the foreseeable future) when using an EFHW with a 49:1 balun? I plan to deploy such an antenna in an inverted-V configuration to try to squeeze 20 meters of AWG12wire into 12 meters of available space on the side of my small lot by running the wire through a ceramic insulator that's zip-tied to a 9.4 meter aluminum mast around 8 meters up. I'm wondering if I'll need a common mode choke where the coax enters the shack or not. My balun doesn't have a separate counterpoise connector so it'll be using the coax shield. The antenna would mainly be used on 40 meters but (after I get my license, I'll just use it for receiving meanwhile but I want to set it up for transmitting so I don't have to redo it later) I'll also have operating privileges on 15 and 10 meters. Also 2 meters but I'll get an HT for that.

 

[prcguy]

I've built and tested dozens of resonant end feds with 49:1 and 64:1 transformers and within their resonant bands they don't seem to have any noticeable RF riding on the coax. When you get out of band and the SWR starts going up they will then start lighting up the coax with RF. Its a good idea to use an effective RF choke in the coax with these antennas, it will allow you to use the antenna somewhat out of band and may also reduce noise pickup on the coax that can ride up to the antenna then to the receiver.

Is RF in the shack an issue at 100W PEP SSB (barefoot HF rig, I don't plan to use a linear amplifier in the foreseeable future) when using an EFHW with a 49:1 balun? I plan to deploy such an antenna in an inverted-V configuration to try to squeeze 20 meters of AWG12wire into 12 meters of available space on the side of my small lot by running the wire through a ceramic insulator that's zip-tied to a 9.4 meter aluminum mast around 8 meters up. I'm wondering if I'll need a common mode choke where the coax enters the shack or not. My balun doesn't have a separate counterpoise connector so it'll be using the coax shield. The antenna would mainly be used on 40 meters but (after I get my license, I'll just use it for receiving meanwhile but I want to set it up for transmitting so I don't have to redo it later) I'll also have operating privileges on 15 and 10 meters. Also 2 meters but I'll get an HT for that.

 

[jaymot]

I've built and tested dozens of resonant end feds with 49:1 and 64:1 transformers and within their resonant bands they don't seem to have any noticeable RF riding on the coax. When you get out of band and the SWR starts going up they will then start lighting up the coax with RF. Its a good idea to use an effective RF choke in the coax with these antennas, it will allow you to use the antenna somewhat out of band and may also reduce noise pickup on the coax that can ride up to the antenna then to the receiver.

I have a dozen or so snap-on ferrite chokes that I can add to the coax just before it enters the house, though I don't know what mix they are. They're just the generic RF noise suppressor ones you see on Amazon. Hopefully they'll be enough to keep the (manmade) noise floor low. I don't plan to operate out of band, that would get me in trouble with the NTC (the Philipines equivalent of the FCC) and might get my license suspended. Besides, I'm anticipating that all the fun will be had within the legal ham bands. The rig I'm looking at getting has a built-in ATU which should help with the SWR, though hopefully it should be < 2:1 on 40, 20, 15 and 10 meters anyway. Meanwhile it'll be interesting to see how the antenna performs as a general shortwave antenna.

Thanks for the information. I've read a lot of sometimes conflicting stuff on various ham radio websites about RF chokes and supressors which made me concerned.

 

[K6GBW]

If you are using an EFHW then you likely can get away without a choke on the coax, although it never hurts to have one there. But if you are using a non-resonant wire antenna then the choke will become much more important. I use chokes made by MyAntennas and they are very effective. I also have an MFJ-915 that works pretty well. Basically, the EFHW's generate very little common mode but are longer. The non-resonant wire antennas can be much shorter but will require a choke and probably an external tuner. Given a choice I'd go with the EFHW first unless there is just to way to fit it into your available space. In that case you'd have to use the non-resonant wire and manage the common mode.

 

[jaymot]

If you are using an EFHW then you likely can get away without a choke on the coax, although it never hurts to have one there. But if you are using a non-resonant wire antenna then the choke will become much more important. I use chokes made by MyAntennas and they are very effective. I also have an MFJ-915 that works pretty well. Basically, the EFHW's generate very little common mode but are longer. The non-resonant wire antennas can be much shorter but will require a choke and probably an external tuner. Given a choice I'd go with the EFHW first unless there is just to way to fit it into your available space. In that case you'd have to use the non-resonant wire and manage the common mode.

Thanks for the information. I think I can squeeze 20 meters of wire into my space if I rig it similar to this (not my image.)

If not, I might be able to take what few meters of wire that won't fit and run it at a 90 degree angle. It would have to be on the end with the balun, if that would work. (I'll be using ceramic insulators as I understand that there would be around 500VAC at the two ends.) Rather than using a tuner as in the image I'll be using that 1:49 balun, although I'll try to buy a rig with an internal ATU if the one I want (IC-7300) is available when I go to buy my radio. I have to first have a callsign then get a permit to purchase and possess, then buy one from an NTC-authorized dealer in the Philippines (or else pay a 4000 peso administrative fee for making an illegal purchase such as from HRO or DX Engineering, or via eBay or whatever.) I also have to buy a rig that's been type-certified by the NTC, which is a lot more strict about transmitter ownership than the FCC in the US: I can't just go buy something at a swap meet here, or at least people aren't supposed to.

 

[K6GBW]

If you make an End Fed Half Wave with 63-66 feet of wire and a 49:1 UNUN transformer then you really won't need much of a counterpoise wire. the coax shield will handle it nicely. I've experimented with adding a short counterpoise wire and it make no practical difference. Just make sure you are using at least 15-20 feet of coax and you'll be fine. The length of the main element wire may not be exactly 66 feet unless you like the bottom portion of the band. If you are going to be mostly on voice the wire will probably be closer to 63-64 feet. But make the wire a touch long and trim it back until you get a good match in the middle of the portion of the band that you use.

 

[jaymot]

I've cut my wire to 20.6 meters to give me some extra in case it's needed then will trim it according to what my NanoVNA shows. Good advice about going for the lowest SWR in the middle of the (40 meter) band, which in my case would be 7.1MHz (we're allowed to use the spectrum between 7.2 and 7.3 on a non-interference basis but there are so many Chinese shortwave stations there that everyone just uses 7.0 to 7.2.) Plus 7.095MHz is the daily emergency net's frequency and it would be fun to be able to check in to the net like I hear people doing on my SW receiver (Tecsun H-501.)

I've contacted DX Engineering about their 3/4 inch inside diameter snap-on mix 31 ferrites which they sell in sets of five. I should be able to put three turns of coax in each one, and they tell me that two or three of those may be enough to stop any CMC (although they say some experimentation will be needed.) All five, if needed, should certainly do the trick. I'll add three meters of RG58 between the unun and the LMR240 as RG58 ill be easier to coil fairly tightly. I'll put the ferrite chokes in about 2.1 meters from the unun to let the antenna use that length of coax shield for the counterpoise. I should have enough left for the CMC chokes' turns, 90cm. I can use the 1/4 inch ID snap-ons I already got from them elsewhere, like on my computer cables if needed.

I plan to have an electrician install a ground rod just outside of my window, a grounding bus bar just inside of the window, and run a wire around my (narrow) house and bond the new rod to the electric service's ground rod. The bus bar will give me an easy way to ground my tranceiver and other gear. I'll also install a lightning arrestor near the ground rod and ground the arrestor to it. Hopefully the combination of all this will give me a safe, quiet shack that doesn't generate much RFI but I still have several months in which to do that.

73s.

 

[k8niv]

I'm running 2 of the my antennas 8010's here, one has a cmc choke inline which is the one out front, mounted inverted L, it too has a short run of coax to it.....
The other one, no choke on it, but has the longer run of coax to it...

As for RFI, there's none n the shack anymore, not since I hooked up my ground system, went with a 5/8" ground rod, put n the ground 7.5ft or so, bought a copper ground clamp for the arrestors to mount on, lightning arrestor's busbar on the back of my desk, all my equipment is grounded on it along with my desk top computer, and had a 5ft run of 6ga copper wire going out to the ground rod....and had a short run too to the ground AEP has on my breaker box, it maybe 6ft or so.....the stuff u need, not cheap these days to buy.....