Coaxial grounding - RF ground

Most radio amateurs have heard about the requirement for equipment grounding. After all, many manuals for commercial equipment mention this right on the first pages. Why?

Protection by earthing

Ako ochrana pred nebezpečným dotykovým napätím sa využíva ochrana nulovaním - the metal casing of the device is connected to the earth wire. In case of a failure in the device, the operator of the device cannot be endangered by dangerous voltage.

TVI

Kovové časti zariadenia sú však pri vysielaní v silnom VF poli. Aj napájač môže preniesť na kostru zariadenia VF napätie. Prečo nie sú na potenciáli zeme? Nulovací vodič má totiž zvyčajne značnú dĺžku, takže jeho odpor pôsobením skinefektu (uzemňujeme VF) je vysoký a nedostatočne plní nami požadovanú funkciu. To je dôvod, prečo potrebujeme kvalitnú VF zem. Underestimation can be a source of various problems in the device, including TVI..

Even the shortest grounding has a few meters. Since every conductor through which current flows creates an electromagnetic field around it, it may happen that we 'bring' RF close to another device that cannot handle it. In addition, we may hit an odd multiple of ¼ wavelength, which will manifest itself in such a way that the device will be RF isolated from the ground. Current flows through the path of least resistance, and such a long line exhibits a high, almost infinite, resistance.

Coaxial grounding

A very good solution is coaxial grounding.. Jeho výhoda je v tom, že elektromagnetické pole okolo stredného vodiča nie je vyžarované do priestoru, ale vedené medzi týmto vodičom a plášťom koaxiálneho kábla, a potom zvedené do zeme. Kondenzátor na konci koaxiálu má zviesť prúd z plášťa koaxiálneho kábla späť na živý vodič.

In my case, the grounding is implemented with a 2m long rod. It is buried by the wall of the house. The coaxial cable is RG-213 about 10.5m long. It is also possible to use another quality coaxial cable. Its impedance does not matter. The connection between the grounding rod and the coaxial cable is precisely protected against weather influences. The termination in the ham shack is with a PL connector. The capacitor is mica, for high voltage. Its capacity is 3.3nF. Perhaps even better results could be achieved with an 'artificial ground' - a tuner that optimally tunes the grounding on each band. I have nothowever, tried.

Return currents

As a prevention against back currents from the coaxial cable, I have snap-on ferrites at the balun on the antenna.. Okrem toho sú takéto ferity aj na prepojovacích kábloch medzi TCVR – PA – dolnou priepusťou. „Prestrihnú“ tak zemné slučky v zemnení a spojoch zariadení.

Despite this, I did not escape problems with TVI.. Začalo pred niekoľkými týždňami, keď si sused zaobstaral digitálny satelit. Rušenie vznikalo aj pri výkone 5W. Každý rádioamatér, ktorý sa s podobným problémom stretol potvrdí, že je to nepríjemná situácia. Napriek dobrým vzťahom so susedom ten trval na oprave môjho zariadenia alebo zastavením vysielania. Pomoc v podobe zaradenia filtrov k TV či feritov odmietal.

In this deadlock situation, I turned to OŠD TÚSR. They promptly came, conducted measurements, and together with the neighbor found out zlý SCART kábel medzi satelitom a TV. Tu musím povedať, že toto bolo nad rámec ich povinností, čo veľmi oceňujem. Teraz nie je so 700W na televízore ani stopa po rušení.

Literature:
[1] https://www.remeeus.eu/english/hamradio/artificial_ground.htm
[2] www.radioworks.com/nbgnd.html