Ham Radio END FED Dual Band 20m & 17m DX Antenna You Can Build.
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- เผยแพร่เมื่อ 26 ก.ย. 2024
- End Fed Multi-band half waves normally rely on harmonic relationships. This one created by Peter G3OJV, offers resonance on two very close bands. Impossible? No it can be done! Great for portable operation.
• Antenna Traps You Can ...
• Low Cost EFHW Antenna ...
Gracias for the presentation, I built a 20M half wave using the 2643251002 ferrite cable core and it worked very well with a transformer efficiency approaching 90%. But adding 17 meters via a trap creates a different dynamic. First, by shortening the antenna (the slight center loading effect of the trap and the slight base loading effect of the transformer) I can now mount it vertically for that better low angle DX pattern, yet the shortened antenna (center loaded and closer to the voltage point) should make the antenna, about 26' long, instead of 32', and only slightly less efficient on 20.... so the compromise is minimal. You will still get a low (DX) angle of radiation; no radials are needed; and with care, no common mode. Easy to mount vertically (in my case anyway) instead of in a a sloper form, and you get 2 bands which is a win-win in my books.. TNX... VA7AA/XE1
Two of my favourite bands. I built this 20m + 17m Antenna using a 4cm plastic pipe with 8 turns 1.2mm solid insulated wire. Across this I put 4x 100pf high voltage caps in series, which measured 25pf across the coil and resonated at 18.100Mhz. The wire lengths similiar to your article. I used a 10m fibre pole without the top 2 lengths. This was the same overall length as the antenna wire. Installed as a vertical with the pole top end going through the coil former to retain the wire. The final vswr adjustment 10m at 1.12 and 17m at 1.23. The EFHW transformer was now common standard design but without and 100pf cap better swr without it. First QSO on 17m on FT8 was with VP8LP in the Falklands at 30w and good results on both bands. Perfect for small garden and a very capable DX antenna. G4PEY
Great to hear from you Ralph and glad the antenna is working out good for you. Take care. 73 Peter.
Again, you prove to me this is the BEST TH-cam radio channel. Always helpful, clear and on point.
I have wanted to build a 30-17-12m antenna. Maybe this is the technique for it.
Wow, thanks! 73 Peter
With an EFHW, you need half the number of traps you would on a dipole! :-)
What a great topic to introduce for the weekend. Thanks Peter. Out with my KX3 today and this will be really useful now that the bands are opening up. 👍🏻👍🏻👍🏻
Have fun! Many thanks for your support. 73 Peter
I built myDual Band EFHW yesterday and its working great. Thanks for the great idea...W6QR
Great to hear from you Bill. Take care. 73 Peter
well done Peter, you are getting good at this.
Many thanks. 73 Peter
Great video, well explained Peter 👍👏👏
Glad you enjoyed it. 73 Peter
cracking video Peter thanks.
Glad you enjoyed it. 73 Peter
Many thanks. Lots to read up now.
Glad it was helpful!
They keep getting better 👍
73 Rob G3RCE
Many thanks. Take care. 73 Peter
This sounds good but what about the efficiency compared to a regular dipole on the same bands is it worse or just as good??
Any loss will be in the transformer. I have never noticed any loss and ther3 are thousands of these transfornpmers used by happy hams. 73 Peter
Great video. New to hf, and really like the idea of having 17m and 20m in an endfed. Would be a good fit in my available space at home.
What commercially available 17 m trap and 49:1 (?) balun would you recommend?
I would love a 17m and 80m commercially available trap? Sources?
Ah yes, seen this design shown by W7ARK on qrz forums recently. Very good. One thing (apologies if I missed this), on 20m fed with 49:1 we also get a very good match on 10 as a full wave. I notice your sweep went from 9-19 MHz or thereabouts, did you see if there was any harmonic resonance above 19 MHz? I only ask this as sometimes amending antenna designs can bring in unexpected bonus harmonics. It may well also be the case that the bands in question need to be fairly close together. The efhw has current maximum in the centre, so for example a 17/15, 12/10 version would be ok but maybe 10/17 and certainly 10/20 (just to try and lower the radiation angle on the full-wave 10m section by turning it into a half-wave), might not be a great idea as both see a trap around the current maximum of the lower band and might go some way to impede performance on the lower band.
The antenna does not work well on 10m. You must remember that the trap has a big effect on the normal harmonic expectations. I may do a follow up video to explain why this happens. Thanks for watching. 73 Peter.
@@watersstanton as I suspected
do you sell this antenna?
Can anybody share an EZNEC model for this?
Hi, if you have a 40m efhw will this technique work to get 40/20/17?
Not 17 as tgere is no harmonic relationship with 40m
Hi Peter. Is it critical to set the trap frequency mid the 17m band or do the antenna wire lengths actually pull it all in to tune on the 17m and 20m band? Thanks for the videos.
Not critical at all. Just set the trap anywhere in 17m when not connected. Any slight pulling has no effect on the results. 73 Peter.
Great video, thanks! How do you like the K4?
Will let you know soon. 73 Peter
"I'll leave a link in the description" - you says. Can't find it, I'm afraid! :-)
Sorry but link now there
Hi Peter, I had two thoughts on achieving this... 1) a trap, as in the video, but also 2) a "fan" like in a fan dipole. I think a fan might be a problem if there are harmonically related bands, but for 20m and 17m it might just work? Worth a try? You then get a full half wave on each band.
I've just seen your latest video. In theory, a fan antenna would then also work on 10m I would guess as you retain the full half wave on 20m?
Guys, nice idea but. i have tested it and it dies not work. I will explain why in a future video. Sorry! 73 Peter
I'm going to make a complete stab in the dark here, but I would guess that a centre fed fan dipole (or ground plane vertical) works because the lowest impedance is at the feed point when resonant, but with an end fed, the non resonant wire would exhibit the lower impedance? I could be completely wrong...! :-)
A dumb but honest question: How many antennas does the average ham radio operator owns or should own? I know you can get multiband, but most youtubers advise that they are not as efficient as a dedicated antenna, your comments are welcome. Do I really need an antenna for each band or can I get away with a multiband one. I am ready for the foundation exam out o f curiosity, I am still researching the hobby's usefulness beyond exchanging a call sign with a stranger in Africa.
Gorge, I have an end fed 66ft 40m-10m and a vertical for same bands. Generally the end fed is better. Most who criticise this antenna have never use one and simply believe what they have been told.. 73 Peter
It's not an easy question to answer as each situation is different. For example, if you have a mono band half wave horizontal dipole, it will be a bit directional, and will give the best transmission/reception perpendicular to its length, with nulls where the ends are pointed. This is the same for the primary frequency of an end fed half wave multi band antenna. As you go up in frequency to higher harmonics, you get progressively more "lobes" and so the antenna becomes more omnidirectional. This would compare unfavourably with a half wave on that band if you are making a contact perpendicular to the antenna, but favourably if it's not in one of the two directions.
If you have the antenna set up as a vertical, sloper or as an inverted V, then transmission/reception patterns become more omnidirectional anyway, and there may be very little difference between monoband and multiband.
A trapped or loaded antenna may not be as efficient on all bands as a full sized antenna, but something like an end fed half wave is full sized on the lowest band, so it is just as efficient as a dipole, minus the small transformer loss.
Experimenting with antennas is one of the joys of the hobby...the hobby doesn't have to be useful, it can just be interesting.
Peter in what arrangement do you use it horizontal vertical or sloper of doesn’t it really matter?
The choice is yours. You may find dimensions differ by a small amount but should work same as any dipole. Peter.
Thanks Peter. I’ve made the trap , can you confirm the frequency to tune it to on the analyser?
Adjust it for 18MHz. It is not super crytical.
I haven't had a garden in years
Is it OFCOM compliant?
It is not the antenna that is compliant, it is the proximity and power.
@@watersstanton Lucky for you got a big garden. Mine is 15ft by 8ft
These videos are great. Your presentation technique is so calm and uncomplicated. They motivate to try things because you focus on the simplicity of the approach. Looking forward to more.
Glad you like them! 73 Peter