My HF antenna in a small garden project continues

Okay Ivan, Now I understand.
So the pull-rope will have a constant bend radius around the yoyo drum. Now it all makes perfect sense 

I have a few months to think about this, but it sounds like a good project.

The present multi-band antenna (without coils) still needs a bit of trimming, but it is really useable from my restricted garden. I have contacts along the Mediterranean every weekend. The VSWR is acceptable, but can be improved when the weather improves. This evening the forecast was for more snow. We have already had 5 or 6 cm and they are promising us another 200cm in the next 24 hours or so.

During the past week I was laid off work because of the corona virus. Last week a guy came to work as usual, but he was already tested positive for the virus. He said that it didn't count because he had antibodies. He worked last week for three days with the RF-team. So we were all sent home. After my quarantine I returned to work only this morning. My mandatory test was negative.

During that time I started on another project that has been shelved for 6 years. But as soon as I finish the antenna I will have it all documented and put on the homepages.
So every weekend you will find me, usually Sundays, on 18MHz and 14MHz. Weekdays I can only use 7MHz since the bands are dead after dark. But come the Summer, I will have daylight from 3AM to midnight. Then I will be burning a hole in "the luminiferous ether" during weekdays 

Ok Ivan, thank you very much for all your comments and explanations.

Best regards from Harry - SM0VPO

Hi Harry,
I  thought the yoyo might be made the same way as a winding drum of a mine winder - the rope wound in a single layer on a wide cylinder. I have not done the calculations yet. This solution may lead to huge diameters of the drums.    On the other hand the radius is constant and the rope never crosses itself.

VBR from Ivan

Hi again Ivan,
I do apologize for the delay. We have had a bit of snow here in Märsta, and temperatures as low as -12'C. By Sunday we are expected to see -15'C.
I cannot finish the antenna trimming but I have been busy trying to rip down all the Christmas decorations.

As regards the antenna drawing you attached, I have studied it for a while and it certainly looks quite good. One small question;

In my yoyo, there are two wheels, one to coil up the dipole wire and the other from which the guy-rope is pulled. This means that as the rope is pulled, the rope-wheel diameter will become smaller and the wire-wheel diameter increases. This means that the wire-length to rope-length pulled will not be a constant. Do you mean that the two wheels at the winch should have the same variable ratio?

Best regards from Harry - SM0VPO

Admin wrote:
1/ If you could provide a quick drawing then I would be very grateful.

2/ I have a load of thick, single-strand, fishing line that I was thinking about using. Flag-rope is ok, but it can soak up water and become stiff when it freezes.

3/ Adding a weight to the line would keep the tension and reduce the load on the gears. However, the weight fixed to the line would restrict the amount of line that can be winched to the height of the mast.

4/ ...it will have a very low visual profile. It is just the yoyos that will attract attention.

5/ It is not so easy to visualize it, especially with a 69-year-old brain

Hi Harry,
thank you for your response.
1/ Here you are - I modified your drawing, I hope you do not object.



2/ The single stranded thick line may be too rigid. I had a polypropylene rope made for yachting in mind. Polypropylene repels water, it does not soak. A multi stranded rope is flexible. These ropes are not enormously expensive and are available in a range of colors and diameters.

3/ I do not understand this paragraph. My 61-years old brain does not recognize what you mean...  

4/ Hide the yoyos inside plastic boxes painted like cabins and tell everyone you are building a model of aerial cable tramway.  

5/ It must be a treat for a super-intelligent knowledgeable and experienced brain, no matter how young.

VBR from Ivan OK1SIP

Hello Ivan,
Thank you very much for the comments. Really interesting.
I like the idea of doubling the ropes on the yoyo to get a much wider range, I think I understand what you mean.

You wrote: (The variable length dipole was my idea originally, Glenn suggested its excitation by a parasitic element later. )
If this does end up with another article for the homepages, then I will be sure to give full credits to you.

I must admit that I was "blinkered" with my own situation whereby I only have only 9 metres of space, so my antenna would need to vary from 14MHz to 29.7MHz, that is 5 metres to 2.5 metres in length. But a published design should include lower bands for it to be useful for other people - longer ropes and lines.

If you could provide a quick drawing then I would be very grateful. One consideration could be that the yoyo spool taking the dipole wire would have a much greater diameter when the dipole is short (lot of wire coiled up). This means that the diameter of the rope/line spool should be quite large.

I have a load of thick, single-strand, fishing line that I was thinking about using. Flag-rope is ok, but it can soak up water and become stiff when it freezes. Fishing-line also has a much lower wind-profile.

You wrote: A slight problem is that the yoyo travels along almost all the length of one half of the dipole. The tension retaining weight travels up and down the same length. This would require the lower ends of the inverted vee (and the whole dipole) to be placed fairly high.

As regards the ends, I was toying with the idea of having the end weights on a second pulley so that the weights would only rise by 50% of the antenna length change. I have 3.5 metres of height at the ends of the dipoles, but only 2 metres height at the support post (the neighbours fence).

I am also thinking about the winch. I do not want to buy anything expensive, so a simple 3D printed winch using a 540 model motor and one cog/spool should be sufficient. Adding a weight to the line would keep the tension and reduce the load on the gears. However, the weight fixed to the line would restrict the amount of line that can be winched to the height of the mast.

There are a lot of ideas and it is just to see what can be done. One of the biggest advantage of this system is with only one dipole and thin fishing-line it will have a very low visual profile. It is just the yoyos that will attract attention. I expect that this project, it it does get built, will be built in several stages with "add-ons" to improve the design.

Thank you very much for your great ideas. I will look forward to seeing a quick drawing. It is not so easy to visualize it, especially with a 69-year-old brain

Very best regards from Harry - SM0VPO

Hi Harry,
you got rid of the sliding contacts nicely. I felt those contacts were a problem from the beginning. (The variable length dipole was my idea originally, Glenn suggested its excitation by a parasitic element later. )  A slight problem is that the yoyo travels along almost all the length of one half of the dipole. The tension retaining weight travels up and down the same length. This would require the lower ends of the inverted vee (and the whole dipole) to be placed fairly high.
I suggest a modification: the winch would have 4 bobbins. two of them of double diamater than the other two. It is due to the fact, that if one bobbin takes 2 m of the rope from the yoyo, the yoyo holder travels 1 m and the other bobbin must release 1 m of rope at the same time. The bottom pulley is movable up and down slightly just to compensate irregularities of the movement and is pulled downwards by the tension retaining weight. One rope goes from the winch via the upper pulley to the yoyo, the other rope goes from the yoyo holder, via the bottom pulley and back to the winch. Is this clear or should I draw a pictue?
Anothr issue is to keep this system working all the year round. The ropes must be waterproof to stay insulating during rains. Strong winds may clutter the ropes and wires. If ice builds on the pulleys and ropes, the dipole will change to a single-band till spring.

VBR from Ivan

Hi guys,
I am still working on the short antenna projects but I have been thinking about Glenn's idea for a dipole with a variable length, controlled by a light-weight motor winch.
I think that which was described may not be so practical with a sliding contact, but it was a really fantastic "off the cuff" idea. So how about this for an implementation idea?



The "Yoyo" can be made out of the plastic boards that estate agents use to advertise outside houses. Waterproof, thin, light and the construction (like corrugated cardboard in cardboard boxes) is really strong. It can also be easily worked with a scalpel blade. This stuff is free from the gardens of houses that have been sold - the agents often just leave and forget them.

The guide plate and cheeks for the yoyo can be 3D printed, or possibly thin aluminium sheet.

Perhaps HusmanHagberg or Mäklarhuset estate agents may sponsor me and buy all the other parts, if I left their name on the cheeks of the yoyo? 
When I made the Packing Crate antenna, I wrote to Nefab (the packing crate makers) and they published the article on their own homepages. But that was over 20 years ago.

I found that things suspended on wire antennas tend to rotate about their axis, so the pendulum would really be needed. If the pendulum were long enough then it may even work with 50g or 100g, as long as it has a low wind-profile.

Rolling up the ends of a dipole do shorten the antenna length, and this has been proved several time. In this idea there is no bare wire to cause intermittent or noisy contacts.

So what do you guys think? Will it "get off the ground"? Any suggestions or improvements? I really love this forum. It may not be a crowded metropolis, but there are some really great ideas bounced around.

I will not have the time or opportunity to get on with this project until there is better weather, so that gives me a few months to think about it further.

Best regards from Harry - SM0VPO

Hi Harry,
I am glad my opinion helped you a bit. Thank you for your offer of waterproofing spray, but it will be easier to buy it here in Czechia (after the sporting shops get opened again, they are closed due to covid now). I know my son uses such liquid for his outdoor equipment, but I never thought about using it for hamradio!

I am looking forward to your article about a multiband dipole!

VBR from Ivan

Hi Harry,

you have done a LOT of wonderful work. Congrats!
Thank you Ivan. That is real praise coming from you  .I feel I have done a lot of practical bits and had a lot of fun doing it. My wife has encouraged me, and you on this forum with constructive comments, have helped a lot.

* Do you consider adding the 24 MHz and 10,1 MHz bands to the multiband antenna?
24 MHz is not a problem at all. It can replace the 27 MHz, but it could affect the 28.00 resonance. It is just to add another dipole. I have a drawing in progress wich includes the 24MHz band.
10.1 MHz may be a bit more complex. A single 5m dipole but with a 2m dangling extension should do the job without any problems. I may add that later, but I have not used CW for a few years.

* A separate magnetic loop might help to reduce the noise on 3,5 - 3,8 MHz.
I had thought about a separate receiving antenna, but it was just a background thought. Yes, the ML antenna could be perfect for that use. I had forgotten it. I will see how time goes and what I can do. I really would like 3.5 MHz, but that will require some more work. Thank you very much for the idea 

* How do you use the waterproof spray?
Simply spray it over the Balun and the connections to the balun ends. When I had the coils I sprayed it all over the coils, but with this antenna I just sprayed everything within about 300mm of the balun.

The spray repels water, prevents snow and ace settling, and even inhibits dirt from settling on the wet surface. It is great stuff.
I saw a youtube video where the inside of a cardboard box was sprayed with the stuff, then filled with water. I tried it and it worked. This is not the video I originally saw, but is shows the principle:

https://www.youtube.com/watch?v=gDTxHlbcRy8

Let me know and I can send you a tin of it. It is the least I can do for all your help.

Ok then Ivan, thank you for your comments. I hafta go now. getting a bit late, but thankfully I am not on call anymore and I have tomorrow off. Maybe get some antenna fine-tuning done and also a bit of operating on 14MHz + 18 MHz.

Very best regards from Harry

Hi Harry,
you have done a LOT of wonderful work. Congrats!
* Do you consider adding the 24 MHz and 10,1 MHz bands to the multiband antenna?
* A separate magnetic loop might help to reduce the noise on 3,5 - 3,8 MHz.
* How do you use the waterproof spray?

VBR from Ivan OK1SIP

Antennas never cease to amaze me. It is so surprising what you can learn.
From my experiments I have learned, or confirmed what I already knew or suspected:

1 - Coils can shorten a dipole element physically, but they can dissipate power
2 - Coils reduce the bandwidth quite dramatically
3 - Folded elements are much better but they throw the calculation off a lot (needed to add 30% !!)
4 - Thick multi-strand AC cable gives noticeably better results. Thin wires can get hot at the feed point
5 - Very close spacing of multi-band elements causes interaction that affect tuning
6 - Waterproof-spray for shoes and clothing makes a big difference
7 - Yes, you can get a 7MHz dipole into a 9m wide garden
8 - Just a small increase in height can have a big impact
9 - Short masts do not need to have visible guy ropes at the top. If the mast is sturdy then 1/2-way up is ok
10 - Painting everything black and orienting the multi-elements horisontal reduces the visible profile
11 - Two elements close in frequency can give more than two resonances (27.3MHz + 29.0MHz also shows a 28.2MHz resonance)

I built the MKII multi-band inverted V with only 9m of garden space, but this time there are no coils. Using the pulley on the mast I was also able to compare signals at different heights (do I need a higher mast? - YES). The community guy thinks the new antenna is a lot less visible, even though it is now 7.5m high (formerly 5m).

I went into the attic at work and laid loads of wires on the floor, with marking tape to get the lengths exact. There is a lot of space there.
https://www.google.se/maps/place/GIC+Coffee/@59.5629412,17.8832581,584m/data=!3m2!1e3!4b1!4m5!3m4!1s0x465fbd3cf7025e05:0x177ad036fc60fcc2!8m2!3d59.5629412!4d17.8854468

I replaced my 100-Watt Balun for a 1KW balun, erected my 7.5m mast using TV mount poles, and put up the new antenna on the new robust mast. The results were fantastic:

Now I have almost 1:1 VSWR on the bands 29MHz, 28.5MHz, 27.3MHz, 21.225MHz, 18.1MHz, 14.175MHz and 7.12MHz (a little trimming still needed).
I skipped the 3.5MHz as there is wideband noise at S9+5dB. That band is unusable for me  

Without the coils I saw that the bandwidth became wider. Even the test station on 7.205MHz is about 10dB stronger, because of greater height and the wider bandwith I got by eliminating coils

The 7MHz element was a little strange. I used 10m + 10m. Each 1/2 of the dipole is 5m + 2.5m + 2.5m folded back with about 6cm spacing. Resonance was 9.4MHz, so doubling back an element cause a cancellation. I had to add 3m of wire hanging at each end to get it down to 7.1MHz. Wow, what a huge difference without coils

So I will be creating two new articles on antennas in a narrow garden with only 8m wide (10m possible with "droop"):
1 - The original antenna with many elements and coils - really cheap and quick
2 - Spending a lot of time to get as much as I can in the air without coils

Antenna measurements were also a problem but I found that my 9kHz to 2GHz signal generator gives enough output to give a meaningful reading on my VSWR meter.

I want to thank you Ivan and Glenn for the suggestion and input while I have been working on this project. Lots of ideas and experiments. Experimenting and learning is what the hobby is all about   

Unfortunately I am working during daylight hours, so all my photography has to be done at night. But I have got a few photos that may be of interest. I will post them shortly when I re-write the article(s). It should be interesting to anyone who has a limited space and wants to cover the complete HF bands and still put out a respectable signal. Last night I exchanged 59+ signals with a G/mobile station working from a boat, and Sunday I got good reports from the Mediterranean.

the only other point to note is that my new IC-7300 has fans and generates heat at 100-Watts, so I now run it permanently set to 10-Watts. If I need more power then I can switch in a home-brew linear amplifier, but 250-Watts I feel is excessive.

Ok, I know I am probably re-inventing the wheel, but any further constructive comments would be greatly appreciated.

Finally, Glenn, you really stabbed my interest with the "variable length" antenna and I want to do some practical experiments with that idea. I have my own ideas, such as the "YoYo" idea that I want to try - it will not need any sliding connections.

Very best regards from Harry - SM0VPO

(PS - I was on-call the whole of Christmas. Absolutely no alcohol, but good food in moderation. Probably why I was more productive with the antenna experiments )