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MEF-330-2K-Plus, 80-10 EFHW matching coil for high bands

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7F, May 31, 2021.

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  1. WA7F

    WA7F Premium Subscriber QRZ Page

    So I recently bought the above transformer. Yes, I could have built one as I have all the parts but, free time is a little scarce so I bought one from MyAntennas. Shame on me but, they have good products and if I have to buy something pre-made then it’s a good place to do it.

    I have a couple of questions about the compensation coil for 20m. I believe it is normally “about” six feet from the transformer and it looks like six turns of wire on a 1” PVC conduit or maybe a 3/4” PVC coupling. So it’s maybe in the 1 microhenry range? Does anyone know what the actual diameter and distance is?

    Second question, and the most important at this point since the wire is in air.

    If the coil were mounted at far end of the wire, would a higher inductance be required? I know if I were matching an antenna this would be the case but, we are talking about a multi-band antenna and aligning some harmonics rather than matching the primary band. What inductance and relative distance from the wire end would be needed?

    WA7ARK did this on his recent 160m EFHW project, I’m just not certain how to calculate it for my 80m EFHW.
    Last edited: May 31, 2021
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

    Hi Dave,

    How high is the wire and where will the transformer be installed?
    Wire Horizontal or some other shape?
    What is your dirt under the wire like?
    How long, and how will the coax be routed from the transformer to the station?
    How is your rig grounded?
    Are the supports conductive, and if so, how close to the coax or antenna?
    What are expecting from the antenna of 80/75m?

    A sketch of the proposed install would help me optimize the lengths, coil placement, and coil inductance...
    G0KDT likes this.
  3. G0KDT

    G0KDT Ham Member QRZ Page


    I'm smiling at your post. I am making a shortened (75ft) EFHW for 80 to 10 too.

    I've seen a few designs one which is like Par Endfedz item has a 6 turn coil about 2m from the transformer then a second longer coil about 2.5m from the other end. The one I am making doesn't have the 6 turn coil.

    My understanding is that the 6 turn coil can be altered turn by turn to move the resonance point a fraction in the antenna to optimise which portion of the band i.e. CW end or SSB end it best vswr. I stand to be correcte, but thats what I have read having had hands on the endfeds antenna documentation.

    I am waiting to see where Mike goes with his feedback when he gets your answers about ground, height and coax proximity to metal supports etc.

    As to buying the transformer, I can say that getting a neat and tidy solid wind wither arthritic hands is very tough o_O and I had plenty of time.

    I think these antennas are going to increase here as getting something in small spaces that will comply with new ICNIRP 2020 EMF licence conditions here not to have exclusion areas etc. is getting trickier.
  4. WA7F

    WA7F Premium Subscriber QRZ Page

    Hi Mike and PG,
    Thank you both for your replies.

    Here’s a description of what I have at the moment.

    A 60’ Rohn SSV, no beams on it yet. At 59’ a 160m horizontal end fed headed roughly south. The transformer is a 65:1, it’s grounded to the tower, the choke at 13’ from the transformer and tunes at 1.5:1 or better across 160 and 80m plus 40m with a tuner. This one is working well enough that I don’t to mess with it. It temporarily disconnected and I’m using the coax for the 80m EFHW.

    The 80m EFHW six feet lower at 53’ using 49:1 transformer and 14 gauge insulated wire (Wireman 544.) The coax is choked at 6 ft from the transformer. It runs basically east and slopes at about 60 degrees. The ground slopes downhill towards the east, the far end of the wire is 18 to 20 feet AGL. It started long at 135’ with a six turn coil on 1” PVC conduit at 124’. I trimmed it to 130’ and there was almost no change in the sweep with the primary resonance at 3.375 MHz before and after trimming. I think 80m is seeing the six turn coil as a trap. That makes sense with 124’/.95 velocity factor providing a resonance around 3.375 MHz. So I think further pruning is required but, I have no confidence that a six turn coil near the far end of the wire is correct.

    How high is the wire and where will the transformer be installed? 53’ at the transformer, ~20 at the end insulator

    Wire Horizontal or some other shape? Sloping about 60 degrees

    What is your dirt under the wire like? Rock and decomposed granite, some moisture below a few inches.

    How long, and how will the coax be routed from the transformer to the station? Down tower, to the tower panel and then underground to the house. Currently using LMR-400 but as the tower is completed everything will be LDF4. So 53’ down the tower, 10’ rough at ground level to the panel, 100’ underground to the house panel, 40’ though the house to the operating position. So about 200’. The tower is properly grounded and tied to the electrical service ground. The coax is grounded at the entrance panel to the house as well as the electrical service.

    How is your rig grounded? To the electrical service ground

    Are the supports conductive, and if so, how close to the coax or antenna? The transformer is mounted on 3/4” Teflon (cutting board), the Teflon is bolted to the tower. The nearest point from the tower to the antenna is roughly 6 to 8”. It’s not really feasible for me to hang the transformer in the air like your 160m EFHW.

    What are expecting from the antenna of 80/75m? Primary interest is 75m and 20m with the best SWR50 possible. The K3 will be remotely controlled through a K3 mini from my 89 year old father’s assisted living apartment in Iowa. His vision isn’t that great so I want to keep the operation as simple as possible. It’s Ok if he needs to use the K3’s auto tuner.
  5. WA7F

    WA7F Premium Subscriber QRZ Page

    I should add that I placed the coil at far end because I could find any 1” pvc when hanging the antenna yesterday. If the easiest approach is placement of the coil near the transformer I get out my climbing gear and flip it around.
  6. 2E0VSS

    2E0VSS Ham Member QRZ Page

    The inductor shortened 80-10 is a dreadful performer on 80…
    It absolutely has to be the full 40-41 metres of wire element to get the performance on 80.
    Of course, they are commercially available but it’s a complete waste of time
    Put your energies Into rethinking the thing.
  7. WA7F

    WA7F Premium Subscriber QRZ Page

    Thanks, Mark. I realize this is a compromise to work 80 & 20m off of the same end fed wire. I just don’t want to do a second coax run or antenna switching on this one to keep the remote operation simple.
  8. 2E0VSS

    2E0VSS Ham Member QRZ Page

    I have used the 41 metre wire version and the 21 metre with the 110 microhenry inductor and it was abysmal on 80..
    If at all possible try and get that full element length..
    Good luck anyway with your passion..
  9. WA7F

    WA7F Premium Subscriber QRZ Page

    It’s full length at the moment. Actually, a bit long.
  10. G0KDT

    G0KDT Ham Member QRZ Page

    Space is an issue here too.

    I need to find some plastic pipe and 20swg wire for the 110uH coil here yet. The 20.6m length is giving a nice 1.27:1 vswr at 7.1MHz using coax as the counterpoise. But that coax will need to be next to a stacked 2inch diameter alloy pole.

    Having experimented with a few antennas I am therefore interested in Mikes reasoning and points on the tower and earthing/screening effects.

    It's unusual for Mike not to have laid out a detailed review with suggestions to you David. We'll be patient :) and hope he's ok.

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