On 08/30/2018 11:20 PM, Brooke Clarke wrote: > Hi Bob: > > I would disagree in that ease of jamming/spoofing is strongly related to > wavelength. That's because antenna efficiency goes down as the size of > the antenna gets smaller than 1/4 wave. > So, it's easy to make a GPS jammer (1,100 to 1,600MHz) since a 1/4 > wavelength is a few inches, something that you can hold in your hand. > It's harder to make a WWV jammer (.5, 5, 10, 15, 20 MHz) since a 1/4 > wavelength in in the range of 500 to 12 feet, something that can be > mounted on a vehicle for the higher frequencies. > But it's extremely hard to make a jammer for WWVB (60 kHz) where a > 1/4wavelength is over 4,000 feet. This means an antenna that can be > vehicle mounted will be very inefficient. Note this also means that it's > extremely hard to make a Loran-C jammer. Note that the WWVB and LORAN-C > transmitters run very high power and the antennas are massive.
Locally you can transmit with a much smaller antenna. It's been shown and works. Sweden used to have a network of 212 m towers to jam and spoof Loran-C/Chayka. It was a top secret network. > This also means that if someone makes a WWVB simulator for their house > the signal at the next door neighbor's house is probably going to be too > small to effect their clocks. Magnetic loop works, non-resonant suffice. Magnetic lopp is used for hearing aid, and it doesn't take much. Enough for the house. Not getting you very far though. > PS. Some decades ago I maintained a beacon transmitter "LAH" on 175 kHz > where the rules for unlicensed operation limited the input power to 1 > Watt and total antenna length to 50 feet. Under these conditions the > effective radiated power might be 2 milliwatts, orders of magnitude less > if a portable system. > http://www.auroralchorus.com/pli/1750meter_antennas.pdf > The 137 kHz band for radio amateurs is limited, but with radiated power, and getting up to that power is a great success and considering the band and that one use CW it should be fun. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
