20m compact loop antenna recently added

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Re: 20m compact loop antenna recently added

Post by n0th1n6 on Thu Feb 01, 2018 1:14 am

Hi Harry,

I am interested in the said 3D printed capacitor. I'll just wait. I've seen VK3YE used the same capacitor in his magloop antenna. My only concern now is the weather proofing and remote tuning.

Only 9m x 4m available space for me to put an antenna. I am seriously considering 20m now haha.

Thanks and 73's,

Noli - 4G1ZYS

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Re: 20m compact loop antenna recently added

Post by Admin on Wed Jan 31, 2018 2:51 pm

n0th1n6 wrote:Hi Harry,

I already made a loop antenna for 40m but same concern as the 10m, the capacitor I am using is from an AM/FM receiver. Even at QRP, I read it will heat up very bad. So I am planning on using the gimmick capacitor for 40m with this loop. Think Ill just wait for the sponge version.

Best Regards,

Noli, 4G1ZYS

Hi Noli,
Even a gimmick capacitor can burn with more than just a couple of watts. At the moment I am printing the 3D capacitor for that project. A 3D printed screw-threaded bolt and tuning knob. It will be used to sandwich a bit of foam plastic between two pieces of copper.

But you can use that now with two bits of copper-clad board and use a miniature plastic G-clamp to compress it. The original used two rubber-bands to hold everything together. A bit tight so the capacitance is to high, then slide one copper board out a few mm to get an exact match.

BR Harry - SM0VPO

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Re: 20m compact loop antenna recently added

Post by n0th1n6 on Wed Jan 10, 2018 12:57 pm

Hi Harry,

I already made a loop antenna for 40m but same concern as the 10m, the capacitor I am using is from an AM/FM receiver. Even at QRP, I read it will heat up very bad. So I am planning on using the gimmick capacitor for 40m with this loop. Think Ill just wait for the sponge version.

Best Regards,

Noli, 4G1ZYS

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Re: 20m compact loop antenna recently added

Post by Admin on Wed Jan 10, 2018 12:30 pm

Hi again,
The 80m version smokes because the tuning capacitor will not tolerate 10kV. If you use the same capacitor as I described in the 20m version then it will take a lot of power.
I will publish the new 3D tuning capacitor when it is finished.

I am also making a whip antenna base-loading coil with 3D printed former. I will post that with it. The former has grooves for the cable and a cutout so that wires can be non-insulated and fixed without the possibility of short-circuits.

But like always, this sort of thing takes time, especially when unavoidable things come inthe way and occupies my time, such as Christmas and work.

BR Harry

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Re: 20m compact loop antenna recently added

Post by n0th1n6 on Tue Jan 09, 2018 12:56 am

Hi Harry,

Thanks for sharing this new antenna design.

Not to start a new thread so I will just ask question here, how do I adopt the 20m compact loop to work on 10m and 11m with just the gimmick capacitor. Will it also work on 40m? I read that it will smoke on the 80m version.

Thanks and Best Regards,

Noli, 4G1ZYS

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20m compact loop antenna recently added

Post by Admin on Sun May 21, 2017 8:41 pm

Hi all,
Interesting events this evening. I have been in Spain for a month, so apologize for the lack of activity here. Much to do. The problems in Spain are very different to those in Sweden: the gardner ran the lawnmower over one of the water sprinklers and it rotated 360 degrees. This resulted in the neighbours horse being totally drenched. I went over there, patted and stroked the horse, then gave it some Swedish hard bread and now I have another friend for life :-)

But I brought back my FT101ZD (16kg) and this weekend I wired it up for 12v battery operation. I stuffed it into the compact 20m loop antenna and I was rather surprised at the results: Running 50 Watts CW, the tuning (gimmick) capacitor simply gets a bit warm and the centre-frequency changes by about 40kHz - 50kHz. If I tune the TX 50kHz below centre I can see the VSWR falling from 1.5:1 to 1:1 after about 10 seconds. But there was no smoke, arcing, sparkerlating, corona or other undesirable effects.

Running about 5-Watts average, with peaks of 20 Watts SSB, there is no detuning at all. With the antenna poking out of the apartment window I worked two UK stations and one Netherland station. I did hang a few pairs of socks on the antenna for the benefit of the neighbours. The antenna is about 40m above street level.

Negative effects? Only one. The antenna is about 4m from my TV set the other side of the window. When I key up it switches the TV on, but there is no TVI. No interference with the landline telephone, either. I just had to turn the TV sound down and keep switching it off with the remote.

I developed the balcony antenna in 1996 because I lived in an apartment, but I did have a bit of space on two huge balconies. Here in Märsta I only have a small glassed-in balcony, so the balcony antenna is not practical. But I was surprised at the results and the 5/7 and 5/8 reports I got.

I am presently building a new antenna to take to work with me. The idea is that I will leave the laboratory and drive up a hill then use a 5.4m long telescopic antenna, based on the Balcony Antenna, fitted into a beach umbrella mount. No pruning needed for 14MHz, so I intend to have a daily session from 11AM to 12AM, weekdays, on 14.190Mhz, weather permiting. I have two 12v 12A/H accumulators so I don't flatten the car battery. That gave me 2 hours operating this afternoon, and the batteries were not fully discharged.

I am looking at getting a fibre-glas fishing rod, after Ivan's suggestion, and I thought of fitting a wire to the length of it, then I can coil the rest up at the bottom and make a tapping for different bands, all with one bit of wire. With the fishing rod fibreglass as a coil former, a 2.5m and a 5m rod, then I should be able to work on all bands from 7MHz through to 29MHz, possibly even 3.5Mhz, and without an ATU :-)

I will drop a massage here when I am QRV, so if anyone wants to have a listen for me then it would be appreciated. I will also be on 14.190Mhz at the weekends using the loop antenna.

Very best regards from Harry - SM0VPO

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