Recommend a most suitable 80m antenna

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by PETER2Z, Sep 17, 2018.

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  1. PETER2Z

    PETER2Z QRZ Member

    Well, how do I start. Few years ago I decided to finally get into the HAM world. I have always been inclined towards HAM an CW in particular so after a long research I bought Elecraft K1 dual band kit with KAT1 antenna tuner. What an excellent choice. I looks good, feels like the real thing and I really enjoyed building it. Due to a number of various reasons I did not move forward and my K1 spent about 5 years in a box.
    Due to an ongoing illness and long term treatment invloved I seem to have more time now for hobbies and want to finally take the exam and get a license. I will be getting CEPT Novice class license that allows me to operate on 80m and 15m bands (well, the lower part of those bands to be more accurate) and VHF/UHF bands which I have no interest in. That's what I built my K1 for (KFL1-2 for 80 and 15m band). Unfortunately, no 40 and 20m where most CW seems to be.
    I will be taking the exam in December this year. In the meantime I am learning Morse by Koch method and spending time to complete the equipment needed. I have so far finished alignment of K1 using a signal generator, a scope and dummy load. All went well. The Elecraft user guide is very well written and easily understood. For the time being I hooked up a simple 15m centre fed dipole and am listening to both 80m and 15m bands. The 15m bands has had absolutely no activity during last 2 months. I know this band is greatly influenced by the solar activity and we are now at its minimum but wouldn't one expect to hear at least some activity? I rechecked the K1 alignment to confirm all is ok and it is.
    The 80m band is quite busy in the evenings as one would expect. I am already able to pick up few bits and pieces of QSO's. So I guess my Morse skills are improving.

    Now, the antenna. I need an antenna that works effectively in 80m band and if possible in 15m band as well. Can have a 15m dipole in the attice but prefer one antenna for both bands if possible. Since my rig is QRP (5W) I will benefit from the most efficient antenna I can possible make I guess. A simple centre fed dipole might be the best however due to the space restriction I am unable to bring the feed line to the house (would be very difficult if not impossible). Anything that is centre or a bit off-centre fed is a no.

    A simple sketch of my location is below. My ham shack is going to be in the house on the first floor.

    I am considering a random wire antenna (should be good match for K1 tuner) if I cannot make something better. I am just guessing that a resonant antenna should be more efficient that a non-resonant one.

    This seems to be a good candidate: a multiband EFHW dipole tuned to 80m, something like this: http://vk3il.net/projects-antenna/multiband-end-fed-80-10m-antenna/

    Can you think of some other antenna that would be fit my space restriction and would be as efficient as easily achievable?

    I am not able to erect a mast so Yagi's, GP and similar vertical antennas are no-go.Frame antennas, magnetic loops e.t.c. are not efficient enough for QRP operation in my view.

    I am not after off the shelf products. I need to be a bit frugal these days and want to make the antenna myself from whatever resources I have available.

    Thanks for any input.

    Peter


    80m ant.jpg
     
    KB4QAA likes this.
  2. N8TGQ

    N8TGQ Ham Member QRZ Page

    Sounds like you're well on your way, Peter! I've had good luck with the EARCHI antenna. It uses a 9:1 coupler to a 30' long wire. No counterpoise is needed as long as you have 15 or 20 feet of coax between the coupler and your radio. The internal tuner should be able to match on all bands. You may be able to wind the coupler using one of the toroids you mentioned in your earlier post.
    I have heard very little on 15m lately. Only during the big contests. But once the solar cycle comes back around look out!
    One last idea for you. Find and join a local club if there is one. You'll get lots of advice, access to inexpensive or even free equipment and manpower to help in antenna projects. Plus you will be supporting them also.
    Good luck on your test and welcome to the hobby!
     
    PETER2Z likes this.
  3. PETER2Z

    PETER2Z QRZ Member

    Well, no local clubs around. There are few HAMs around though. I contacted some of them but they tried to put me off any DIY - too time and money consuming with questionable results they said.

    I looked at the EARCHI antennas and (correct me if I am wrong) it seems to be a non resonant random wire antenna. I assume a resonant antenna should be more efficient, shouldn't it?

    I may try those yellow-white toroid cores but I am very hesitant. They come from various switching power supplies and are yellow-white. That should mean -26 material (iron powder) which is good for DC chokes and switching apps for up to about 500kHz. Above that I assume huge losses. Actually, is there an easy way how to measure a balun/unun impedance and loss using a signal generator and a scope? If there is i might give it a try.
     
  4. G3YRO

    G3YRO Ham Member QRZ Page

    Peter you're right in thinking the toroids you have would be completely wrong . . . but ANY end-fed wire antenna that uses a Balun Transformer to try and match to co-ax impedance will always be a poor compromise. (as in reality the antenna impedance will vary wildly from band to band).

    MUCH better to take the end of the wire into a window (preferably upstairs) and straight to an ATU. The ATU then tunes the wire PROPERLY on whatever band you want. (you said you already have an ATU)

    The length of the wire isn't even critical . . . although to work on 80m you would really need at least a quarter wave long - I personally prefer using a Half Wave, as there seems to be less Earth Losses. It also means the antenna will look like high impedance on most of the Amateur Bands.

    A half wave antenna on 80m is about 40.2 metres long, which you say you have room for.

    [​IMG]

    Just use PVC-covered multi-strand wire (I use 24 strands of 0.2mm for antenna wires) . . . and no need for insulators at the ends - even at high power, any plastic string will be just as good. (just knot the 2 together)

    Bear in mind that the wire dropping down into the ATU is all part of the antenna (in terms of total length) . . . and best if the ATU is on the wondowsill - ideally in an upstairs room. If you have a sloping roof (like in the above picture) you don't even need to get on the roof to fix the string holding that end of the antenna wire - just throw it over the roof and tie it into a window on the other side. (that way you get it as high as possible)

    I've used antennas like this at several QTHs in the past, even running high power. You COULD drop a wire connected to the chassis of your rig out of the window to provide an earth/counterpoise . . . but I have never bothered, as the copper pipes going round the house for the central heating as well as the mains earth wiring has always provided a perfectly adequate "other half" of the antenna.

    Good luck!

    Roger G3YRO
     
    Last edited: Sep 17, 2018
  5. WQ2H

    WQ2H QRZ Lifetime Member #214 Life Member Platinum Subscriber QRZ Page

    Looking at your layout - my issue with a dipole would be the feed line crossing over the parking area. It could work but it wouldn't be pretty, especially is you use something like 600 ohm ladder line.

    Intuitively, almost any coil-shortened endfed will lose quite a bit of performance at 80m, so you may want to consider dropping the inductor and look for a standard endfed & network design. I have several custom coil shortened dipoles and while great for Rx, they are only adequate for Tx (a little frustrating on the last ARRL field day).

    I know you're not looking for off-the-shelf, but you may want to consider an Ultimax. They are economical, easy to install, and no one will even know it's there. I have one of the 124' Dxtream versions that I use with a single 60' counterpoise and it is extraordinary (they don't need much tuning at all, but would work great with a QRP tuner such as an MFJ-9201 or anything similar). http://www.ultimax-antennas.com/store/p2/ULTIMAX_DXTREME__.html

    Whatever you decide - good luck!
    73
    Jim, WQ2H
     
    PETER2Z likes this.
  6. PETER2Z

    PETER2Z QRZ Member

    I considered that but I agree it wouldn't be pretty. Also, being an amateur astronomer I setup my scopes in that parking area and want to keep the sky clear of obstacles. I can live with antenna wire but an extra feed line would be too much.

    I am not considering coil-shortened antenna. The available space of 42m ~138ft allows me to fit full half wave length wire at 80m. The VK3IL antenna, I posted a like to above,
     
  7. KC3RN

    KC3RN Ham Member QRZ Page

    I use a similar antenna. It's 74' of 18 gauge THHN (stranded), terminated to this: https://www.ebay.com/itm/End-Fed-Di...nna-Matchbox-System-HIGH-QUALITY/191226640113. From there I run about 50' of coax to my rig. It performs well on both 80m and 15m. It will tune on 40-6m as well, but performance is slightly lower. It doesn't, however, care much for 60m. The internal tuner in my rig handles it quite well. I'm actually thinking of hanging another (shorter) version to handle 40 and 20 a little better.

    I think the key to good performance with this antenna is a few radials. The antenna was okay without, but adding a few really made a difference for me. I'm using 8 random length radials, which range from 12' to about 30'.

    Good luck, and welcome to the hobby.
     
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  8. WQ2H

    WQ2H QRZ Lifetime Member #214 Life Member Platinum Subscriber QRZ Page

    I see - it looks identical to the Ultimax in terms of layout and bandwidth. That loading inductor was unfamiliar but I still believe any loading will effect 80m performance significantly. But if you're only going to use it for CW I'm guessing not a huge loss. Thanks!

    73
    Jim, WQ2H
     
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  9. G3YRO

    G3YRO Ham Member QRZ Page

    If you use what I suggested it will cover ALL of the band, on ANY band . . . and without the losses associated with those types of balun-fed antennas !

    Roger G3YRO
     
    PETER2Z likes this.
  10. PETER2Z

    PETER2Z QRZ Member

    Hi Roger and thanks for your input.

    Why is that you think that antennas that require impedance matching (balun trasnformers) are a poor comromise?
    IIRC from the school, an end fed half wave dipole is a resonant antenna with impedance of about 2kOhms (depends on distance from ground) so in order to match it with 50Ohm transceiver input it requires an impedance matching unit. This is often realized as an autotransformer with ~1:49 radio. I can see there will be losses in the autotransformer comparing to a centre fed dipole but I see them pretty marginal. This kind of impedance is outside of the range of the autotuner in Elecraft K1.

    End fed long wire antennas (you are proposing) are non resonant antennas with impedance of about 500 ohms and require 1:9 unun in order to use coax feed line or need to be connected directly to ATU as you said. I fully agree with that. However, should the wire length by any chance get close to multiples of half wave length the long wire becomes end fed dipole with impedance as I said above. And that is a very different antenna to long wire.

    So, the question is either resonant EFHW dipole or long wire (cannot be 40m long) for 80m band. Again, IIRC dipole has better radiation efectivity as a non resonant long wire antenna. I found this article that shows the differences between centre fed dipole and long wire:
    http://www.iz2uuf.net/wp/index.php/2016/04/26/great-spaces-longwire-or-dipole/

    So, I am still inclined more towards resonant EFHW dipole with matching unit and short coax feed line towards the transceiver than a long wire.

    But all of the above my thinking which may be completely wrong. And even if it is not it is still a theory and long wire you propose is so close to dipole in terms of efficiency that it is not worth to bother. Sometimes the simplest solution work the best.
     

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