EFHW for QRP work


William Fogel
 

I have just acquired two qrp rigs.  One is the 20m Cricket and the other is (TR)u SDX.  I would like to take them both out this Field Day and during the summer to operate outside.  Thinking about an EFHW maybe the ARRL Kit.  Does anyone have another sggestion.  Should I be looking at something specifically for QRP operation?  Am I better off building my own?  I will probably be only operating on 20 &40 but one is capable of voice as well as CW.  and Digital modes as well as 6 other bands. I am curious what y'all suggest, it does not have to be super light weight since I am not backpacking or operating anywhere my vehicle does not have access, too.  Do keep in mind that in the RGV, we are at or below Sea Level and Cactii don't grow very tall!  Thanks for any suggestions.

73 Bill  AG5SK
"this Ham is Kosher!


Shirley Dulcey KE1L
 

An EFHW works best if you have at least one tall support. A typical portable setup has the feed point near ground level (near the radio) and the far end elevated. You can also elevate both ends and run a longer feedline to the radio.

If you're going to set up in a location with no tall trees, you can use a vertical support for the far end, like a collapsible pole in the 20-40 foot range. You'll need some guy lines to hold that up, or you can use a mast support that you drive over with your car (you may still need guys unless you're in a location with little or no wind). Poles from Jackite, SOTAbeams, and MFJ are popular choices. Or you could consider a vertical antenna instead, a topic for another post.

Side note: if you ever want to operate from a tall building, you may not need any supports at all. Run your EFHW down from a window toward the ground. Attach a few feet of twine or rope to the far end so the end of the antenna is not all the way down at ground level, then attach the end of the rope to a ground stake. Or wrap the end of the rope around some convenient object; a short tree, a sign post, or whatever is at hand.

The ARRL kit is one good choice, and it has the advantage of having everything you need including the antenna wire. If you're looking for something less expensive, there are some EFTW antennas that are designed specifically for QRP use; they use smaller inductors and thinner wire, reducing weight and cost. The ultimate in size reduction is the kit offered by K6ARK (https://k6ark.com/); the transformer goes right on the end of a BNC connector.

You're asking the question on the 4SQRP group, so I have to point out the club's new EFHW Antenna Experimenter Board kit (http://www.4sqrp.com/EFHW.php -- sadly out of stock right now), which includes everything you need to build an EFHW except for antenna wire and possibly an enclosure for the board. Using the board bare is fine for temporary setups like Field Day, especially if you're not expecting rain, but you'll want an enclosure for a permanent installation.

On Sat, May 7, 2022 at 1:57 PM William Fogel <wefogel@...> wrote:
I have just acquired two qrp rigs.  One is the 20m Cricket and the other is (TR)u SDX.  I would like to take them both out this Field Day and during the summer to operate outside.  Thinking about an EFHW maybe the ARRL Kit.  Does anyone have another sggestion.  Should I be looking at something specifically for QRP operation?  Am I better off building my own?  I will probably be only operating on 20 &40 but one is capable of voice as well as CW.  and Digital modes as well as 6 other bands. I am curious what y'all suggest, it does not have to be super light weight since I am not backpacking or operating anywhere my vehicle does not have access, too.  Do keep in mind that in the RGV, we are at or below Sea Level and Cactii don't grow very tall!  Thanks for any suggestions.

73 Bill  AG5SK
"this Ham is Kosher!


Rich Clemens
 

I run QRP 100% of the time and use a HamStick tuned with a NanoVNA for the band of choice in a metal tripod (see image) and it has worked wonderful with over 35 DXCC contacts with FT8 in 21 days. Enjoy!


Jim Upson
 

These are in order of my usage OR general knowledge.   As background, here is my operating conditions while on SOTA…
  • Initially KX3 (10-15 watts) but now KX2 (10 watts), both with builtin ATUs
  • Initially Alex Loop, but now LNR 40/20 EFHW,  Packtenna 60m EFHW...inverted-V, 6' coax BNC connectors
  • Sotabeams 10m telescoping pole with homebrew guying ( http://www.qsl.net/wb3gck/guyring.html ) or just leaning against trees
  • Bioenno Lithium Iron Phosphate 12v 3 Ah battery held in a Tom Bihn Cubelet 210 Ballistic bag (next to my body especially during cold weather)
  • Paper logging
  • 'Desk':   9-inch x13-inch kitchen cutting board, currently holding the KX2 with rubber bands (but intend to go to heavy-duty dual-lock velcro).  I hold the 'desk'  against my body with one hand while the other hand is either logging or using the MH3 microphone....this all works quite well.
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1). This has been my 90% of-the-time antenna from Pennsylvania SOTA summits, contacts all across USA, and EU, running 10-15 watts on Elecraft KX3/KX2, inverted-V:  
 
EFHW 40/20 (originally from LNR”, now from Vibroplex and is by far my most used antenna on SOTA):    

 
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2).  EFHW Linked 40 and 20…or just keep it connected for 40, and will be half-wave on 40 and full wave on 20….
 
I’ve not used this exact pre-wired version  (just got it)….but I have extensively used the exact same unun/winder with 87’ wire for 60m with great success for ~1/3 of my SOTA Goat activations (Canada to Florida, Pennsylvania to Michigan….).  By the way, I also used the 87’ wire with the internal tuner on my KX2 to use it on 40m when I couldn’t get enough contacts on 60m ….worked pretty good….
 
 
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3). I not used it….but wildly popular for 40/20 and 10 (originally from LNR, now from Vibroplex:  40=halfwave, 20=full wave, 10=two-waves):
 
 
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4).  EFRW (9:1 unun-Random end-fed)…requires a tuner….also widely popular…I’ve not used this….but I would go out on SOTA with someone whose only antenna was this one…she configured it with a 58’ radiator & 17’ counterpoise and had great success with it:

 
Also this guy made his own…”speaker-wire” random wire antenna……no unun!!….just 28.5’ radiator and 28.5’ counterpoise….connects it either directly to a radio that contains an ATU, or uses a Elecraft T1 external tuner: 
 
 
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5). Another EFRW….requires a tuner…I’ve not used one…expensive….but suppose to be high quality…
 
 
 
 
 


Jim Upson
 

Forgot a pic of my desk:


Ted
 
Edited

Here's an Idea I've followed at least once, though I gave it away with a radio since then:  

Wind a 49:1 unun on a 1/2" yellow torroid, 3 turns primary to 21 turns secondary*.  Use 22 to 26 guage magnet wire.  Fit 10 to 12 ft of counterpoise to the ground side.  Wire a polyvaricon across the output, and add 63' of aerial wire. Tune the length for low SWR to the lower end of 40m with the cap mid-dial.
 
In use, you really only have to trim the cap to maximum audio but you certainly could use a SWR meter at first in order to rest yourself assured. (One could also add a resistive LED SWR indicator and put it in a small enclosure rather than on a kite string handle.) If for some reason you can't get into the voice section of 40m or 20m, feel free to lop off a foot.  
 
K3RTA



* I've been liking the yellow core for lower band work, and the 3:21 has been suggested for the same benefit.  
 

On Sat, May 7, 2022 at 20:53, Jim Upson
<jim72upson@...> wrote:
Forgot a pic of my desk: