Quote:
Originally Posted by WM6
Hi Geo,
You mean end of air cored coil antenna cold wire end connected to circuit ground (similar as on block schema in my first post but without ferrite core) or straight antenna wire end grounded in soil?
In second case (straight antenna wire end grounded in soil) there is no way to proper adapt resistance of 150m wire at VLF band to your amplifier output. But if you insist on this configuration, forget resistance and drive your amplifier at max 25% of its power. Another solution is to use (for <30khz band) an old speaker transformer (for 4-8 ohm speakers) connected in reverse to amplifier (Warning: high voltage at output!) and max. 50% of amp. power. For higher frequencies use ferrite transformer (if you build one on bigger ferrite toroid primary have to be 4 ohms and secondary windings at your wish - say 50Vpp to not be dangerous).
In first case (air cored coil antenna cold wire end connected to circuit ground) you chose antenna resistance according technical specification of amplifier you use, which is in amplifier from post above about 4 Ohms or a little more. You do not need special antenna tunning (SWR) as on HAM bands. Never drive your amplifier at more than 75% of max power.
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Hi WM6. I am interesting for the second case. Frequency will be 100Khz so not so good for audio transformer. Ferrite core maybe is a solution!!!!. I want to have a strong signal at distance of 10...30m far from antenna so i believe that there is not need for high power.
2...3 watts maybe is enough
Regards
