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How to use 80m EFHW on 60m and 160m

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K3RW, Aug 8, 2019.

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  1. K3RW

    K3RW Ham Member QRZ Page

    I have a 80m EFHW that I'd like to use on 60m and 160m if possible. Anymore I run a vertical and do rather well with that, but not enough space for 60m and below radials, so the lower bands 60/75/80/160 would need to run longwire or EFHWs. Not really enough space for a skyloop.

    Anyways, my understanding of the EFHW is that my particular one is an 80m EFHW. Element length seems about right for a 75/80m length.

    To run 60m, some would just tune it as-is, and accept the losses. I'd imagine most would just add enough wire to make it a 160m EFHW, and just tune it on 60/75/80m.

    Is there a better way to do this? Traps/coils/links/etc.?

    I looked into doing it as a multiband fan-type element. Nope. Won't work.

    The part I'm never sure about is the counterpoise length. Some people run NONE, others run a 5% WL, and others seemingly run a halfwave. And given it is intended in my use to be multiband, I suppose I have muddied it further.

    Ideas? I'm up to running it as a random/longwire as well (some disagreement online on the terms). It may end up being easier with my remote auto-tuner if I did so, though not married to the idea of using it--the mismatch could be super high. Big Bertha, the Dentron MT-3000 should match it, then.
     
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

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  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Greg (K3RW):

    There are quite a few wire antenna choices for 160M, including a multiband unit by MyAntennas. But all of them need to be raised above ground and as far away as possible (or perpendicular to) nearby objects, such as metal gutters, other antennas, etc., to perform well

    In general, a good rule of thumb is to try and keep the EFHW wire at Wavelength/2 above the ground and away from surrounding metal objects. As ground gets closer, the radiation pattern tends to become more vertical due to diffuse reflection and absorbtion by the ground, as well as near-field parasitic coupling. Both effects can increase the apparent SWR of the antenna and reduce efficiency/increase losses (a lot) in attached matching networks.

    At 160M, 80M of height and stand-off distance would be very nice. But it's NOT a show-stopper if you can't manage that. It's just that the lower and closer the antenna gets to the ground, the less efficient it becomes. At QTH#1, I have a 160M EFHW that, at its peak, is only about 30 feet above the ground, and at other points, its much lower. To make it worse, portions of the antenna run very close to two homes with aluminum gutters/downspouts and stucco/embedded chicken wire construction. Such is urban life.

    I've made a fair number of DX contacts with it, and many more that are relatively local. It works, but it's certainly not terribly good, due to the install constraints. I have a nefarious plan to get it up another ten feet without too many neighbors noticing, which I think will help a bit. But I do wish I had Mike's wide open space near his hanger, in the desert, or in a forest of tall pines, at a break in the tree line.

    60M is another story. It's a very restrictive band with strictly defined channels, power limit and bandwidth limit. There are very few antennas designed specifically to cover this band and it has relatively little activity - but its ALL concentrated in those narrow channels, so it CAN be a lot of fun to operate. I like to run FT8 on 60M. This band may best be operated with a homebrew antenna, wire or otherwise. Perhaps Mike's design can be adapted. I use a CHA-250B. Many consider this a broadband vertical dummy load, but it works pretty well on 60M (especially compared to nothing at all), and I've had some good fun with it. No radials required. But not cheap, either.

    For digital modes, other than the usual 20M during the day, 40M in the evenings and 80M late at night, 17M is often also great during the day, and less crowded than 20M, which can mean easier contacts, and more of them. 30M comes alive in the evenings, and recently has had 6,000 - 8,000 mile windows open frequently in the early to late evening hours, workable even with the 200W power limit on this band, from my EFHW-8010-2K. These are easy bands to get on with either a rotatable dipole or wire antenna.

    Hope this ramble helps, or is entertaining, at least! I'm sure you are aware of most of what I mentioned, already.

    Have fun!

    Brian - K6BRN
     
    Last edited: Aug 9, 2019
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  4. WA7F

    WA7F Premium Subscriber QRZ Page

    I’d default to non-resonant Inv-L. Get it as high as practical but, it works more like a vertical so the height isn’t critical. Use a remote tuner at the base to keep line losses down. They work surprisingly well even with short radials. I’ve had a lot of fun on 160 -10 with a 130’ insulated wire Inv-L.
     
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  5. K3RW

    K3RW Ham Member QRZ Page

    I did just pickup a SGC remote tuner a couple of weeks ago.

    Hmm, what length would I want to run it as a non-resonant for 60/75/80/160m? This site gives 'random wire lengths' to avoid https://udel.edu/~mm/ham/randomWire/ but I think that's not what I would need, correct?

    After some further research, I'm inclined to do it more this way. I forget that on 160m an EFHW is a half-wave. Durrrrr. :confused:

    If I don't have the space for a 80m dipole, I don't even have space for this 80m EFHW as-is!
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    A horizontal wire, which is 0.484 wl (257.4ft) long, 0.1wl (50ft) above average dirt, is resonant at 1.85MHz.
    That same wire has its third harmonic resonance at 5.66MHz.

    If end-fed, both odd and even harmonics are useful. The second harmonic lands in the 80m band, the third lands at 60m, the fourth at 40m, and so on. That is the key idea of EFHW antennas.

    If center-fed, only the odd harmonics are useful. The third harmonic lands in the 60m band. Non of the other harmonics are useful.
     
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  7. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Mike:

    Why are the useful harmonics different on an end-fed vs. center-fed wirw antenna arrangement?

    Thanks!

    Brian - K6BRN
     
  8. WA7ARK

    WA7ARK Ham Member QRZ Page

    A center-fed 66.2ft long wire at 30ft agl over average dirt exhibits this familiar variation of R and jX and SWR near frequencies where it is one-half wavelength long (7.15MHz), as shown in the left panel. The behavior is similar where it is three-half wavelengths, five-half wavelengths and so on...

    odd.png even.png
    (Click to enlarge)
    The plots in the right panel shows the typical behavior of R and jX and SWR near frequencies where the 66ft wire is one wavelength long (14.2MHz). The behavior is similar where it is two wavelengths, three wavelengths and so on...

    So, on odd harmonics (including the fundamental), the impedance is low enough that coax can be used for direct feeding. Not so on even harmonics. You would have to use a transformer (not unlike the one used with an EFHW). For a multiband antenna, the transformer would have to be switched in/out on a per band basis.

    I showed how every harmonic of an EFHW is useable in the slide show (slides 24 to 26), including how to better align the higher harmonics with the band centers using the compensation coil. Basically, every harmonic has a similar rate of change of R and jX around each resonance.
     
    Last edited: Aug 10, 2019
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  9. K6BRN

    K6BRN XML Subscriber QRZ Page

    Mike (WA7ARK):

    Thanks. The illustration of current nulls (pretty much a wave diagram) on slide 25 is particularly useful in understanding what is happening.

    It also illustrates in one conceptual snapshot the key advantages and disadvantages of both center-fed wire antennas (no matching transformer needed) but covers only fundamental and odd harmonics, and an end-fed wire (covers odd/even harmonics) but requires a matching transformer.

    Very usefule package. Thanks again for posting it.

    One comment with regard to pattern peaks and nulls is that, from experience, when bent into a horizontal V, at various angles, the peaks and nulls in the antenna pattern appear to blend together, yielding a nearly omnidirectional pattern. At QTH#1, with about a 43 degree included angle, a simple geographical scatter plot (EFHW-8010-2K) of digital contacts on 15M, 17M, 20M, 30M and 40M provides some evidence of this. No deep nulls are evident. The wire is up about 23 feet and at the V endpoints IS very close to my home's aluminum gutter network. So that might affect the results somewhat. It is a remarkably successful installation - still the best performing one I've done to date, with regard to directional versatility and overall effectiveness.

    Best Regards,

    Brian - K6BRN
     
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  10. K8JD

    K8JD Ham Member QRZ Page

    How to Make a 80 M wire Work on 160M ?
    Make it twice as long !!!! :rolleyes: This is TRUE !
     

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