This is where I’ll work on the information available about the KGD Antenna. The centre coil form apparently used to be sold as a kit by QRP projects in Germany.
To simplify the process – I hope – I’ve tried generating a rough first pass translation via Yahoo’s Babelfish site. I’ll work on that as time permits.
Just like a segment a week or so ago on the ABC TV Music Quiz show ‘Spicks ‘n’ Specks’ where contestants had to guess the song after the lyrics were translated into Japanese and back again, these translations may be more hilarious than informative, but it’s a start…
The part following this English page re-write is sourced from the copy on the main web page. There is some overlap with the pdf file also translated later on this page:
lightly edited English translated page:
Lots of hams are not able to install a standard antenna. Some German QRPers designed the KGD – that’s a German nickname for a ‘very short dipole’, that can help these friends because it’s really small but very efficient.
The 40 metre version of the KGD is only about 150cm long. The dipole is made from two 20mm diameter aluminium tubes and two 18mm diameter coils.
The middle of the KGD is made from polyamide. The coils are wound with 0.8 mm enamelled wire. To match the 50 ohm coax impedance, we use a capacitor rated at 6 kV.
(This diagram shows the dimensions of the turned centre coli former. It’s intended to hold aluminium tubes of 18mm internal diameter – presumably so their outer edge lines up with the end of the coil space.)
There are short tuning rods at both ends of the KGD. Tuning is very reproducible. We tested ten KGD 40m antennnas and they all tuned up within +/- 5 kHz of the same frequency. Bandwith for VSWR 2 is about 45 kHz at 40m
We used RG58 coax to feed the KGD. Our special mast to antenna holder is designed to enable horizontal or vertical mounting on a fishing pole. If the KGD is mounted vertically, the coax must be attached at a 90 degree angle for at least one metre.
The QRPproject KGD is limited for 100 Watt RF power maximum
We ship KGD kits from stock. The coils are pre-wound and the capacitor installed. You only need to add the tubes and the coax.
Take care that no one can touch the KGD during transmit. Even with five watts there are extremely high voltages at the dipole.
The KGD is not longer available.
KGD – Short ‘sawn-off’ dipole
Drawing on recently published material a small DL-QRp-AG working group developed an antenna for those with restrictions on what they can erect. We call this antenna
the KGD = (K) urz (G) eratener (D) ipol or Short ‘sawn-off’ dipole
The 40m band version of the KGD antenna is exactly 150 cm long (4ft 11in)and 2 cm (3/4in) diameter. The special feature of the KGD is that it is incredibly immune to the environment, and it performs well. Essentially it’s a system with two series resonant circuits and a tube (?) capacitor. With a transmit power of just 3 watts fed to the antenna, a voltage tester 10cm away glows like a Christmas tree. In practical testing there was barely an S-point difference with the G5RV on the other side of the house.
The KGD was originally launched in two forms: a simple homebrew version and a kit. This data here outlines the simple homebrew version and there used to be a kit available with the turned centre section made from Polyamide, with ready-wound coils and the pipes prepared and cut to length. So there used to be a choice to build the KGD completely or buy the kit. The kit is no longer available.
The coil form of the QRPproject version was made of Polyamide. The spaces on the left and right were supplied pre-wound with 0.8mm diameter (18 awg /21 swg) copper wire. A fixed capacitor was inserted to match the cable impedance to the feedpoint resistance of 20 ohms. The OMs tried to couple the 2:1 balun directly without a fixed capacitor, and likewise coupling with condenser and using a 1:1 balun was quite successful.
The centre section of the KGD can be made weatherproof by covering it with a heat shrink sleeve. If the KGD is to be installed outside permanently, we recommend enclosing the centre section in a plastic tube.
There are tuning rods at both ends of the dipole. They can be adjusted to balance out any possible environmental effects. On the most critical band – 40m – all the KGD antennas tested so far were able to be tuned in each band segment. The range between the points where SWR was 2:1 was about 45 kHz.
RG58 coax is used to feed the antenna. The mast support (KGD-MH) was arranged so that the dipole could be fastened horizontally or vertically to a mast or a fishing rod, or it could even be screwed to to a roof slat. When mounted vertically the coax cable must be led away from the dipole at 90 degrees for a metre or two.
The KGD from QRPproject can handle up to 100 Watts, but as staunch QRPers we consider this a waste of energy
If the resonant frequency is below the respective band, then the antenna is tuned by unwinding a turns. NOTE: Always remove only one turn from each side at the same time and measure again.
|Pipe length for each side||Turns 0,8mm copper wire per side|
|80m (no kit!)||160cm (20mm ID)||258 turns close wound on 20mm core, adjustment with coupling coil|
|40m||70cm (18mm ID)||114 turns close wound on 18.5 mm core adjustment also with tap with 1,5 Wdg or condenser 470pF|
|30m||50cm (18mm ID)||71 turns close wound to 18.5 mm core adjustment with condenser 330pF|
|20m||35cm (18mm ID)||47 turns close wound on 18.5 mm core adjustment with condenser 220pF|
|17m||30cm (18mm ID)||35 turns close wound on 18.5 mm core adjustment with condenser 220pF|
Please note: production of the KGD has ceased. The only option available now is to build it yourself.
This is the copy appearing in the pdf at the ‘Baumappe’ link at http://www.qrpproject.de/Media/pdf/kgdmanual.pdf.