| Home |
| Search |
| Today's Posts |
|
#11
September 9th 11, 02:03 PM
posted to rec.radio.amateur.antenna
|
|||
|
|||
MFJ-868 SWR/Wattmeter
Dave Platt wrote:
In article , Jim Lux wrote: Well.. Consider a 20 meter long wire hanging 10 meters above the ground (half a 80m dipole) so now you're talking tens of pA, 100 Meg isolation isn't hard to get with clean insulators. That 20 m wire is like a 850 pF capacitor. If assume, say, 25 pA charging current, you get a volt every 42 seconds. After half an hour or so, you're up to 40 volts or so.. Granted it's not a lot of Joules.. (heck, probably not even a microjoule).. So fair weather charging isn't likely to kill your MFJ.. Back to the dust/rain/induction charging, which can certainly get the levels needed. I've observed clear-air charge on a TV antenna (about 30' above ground level) which was sufficient to create a visible spark when I touched the center connector of the coax to a grounded static-drain block. No rain at the time, no appreciable amount of dust (SF Bay area)... just clear air with a mild breeze. Were there any elevators nearby? |
| Thread Tools | Search this Thread |
| Display Modes | |
|
|
Similar Threads
|
||||
| Thread | Forum | |||
| MFJ-868 SWR/Wattmeter | Antenna | |||
| MFJ-868 SWR/Wattmeter | Antenna | |||
| Wattmeter help | Antenna | |||
| WTB: LDG DWM-4 wattmeter | Swap | |||
| FS: HF/VHF/UHF wattmeter, URM-120 | Swap | |||
Threaded Mode
