[Elecraft] Polarization loss [was "no subject"]

[Fred Jensen]

On 2/12/2014 12:46 PM, Edward R Cole wrote:
> Ralf,
>
> Thanks for catching my mistake in the ohm's law formula.
> P = E^2/R

It's been at least 100 years since I worked antenna problems out on my 
K&E log-log duplex vector slide rule, but the rule of "20 dB loss with 
crossed polarization" doesn't apply well [or at all] in the near-field. 
  And, the near-field doesn't just suddenly end, it declines as 1/d^k 
where k is usually somewhere between 2 and 3 depending on a bunch of 
other factors.  The result is that the NF fades into the FF, there's no 
sign out from the antenna that says, "The Far-Field starts here."** :-) 
  Again, I would be extremely careful connecting a second antenna to a 
receiver if the antennas are at all close.  Many a radio has been fried 
on Field Days.

On the subject of destroying the front end of a receiver, be very wary 
of precipitation static with ungrounded antennas.  Each rain drop or 
snowflake deposits a tiny charge.  In the absence of some path to 
ground, each tiny charge will add to the total charge on the input 
capacitance of the first stage [like an FET], and eventually the voltage 
will rise high enough to destroy the device.  I believe Elecraft radios 
have internal bleeds on the antennas but I still have external ones on mine.

The same crew with over 200 hours of aggregate ham experience that put 
the CW and SSB stations in the same cabin watched a tiny little bit of 
"grass" on the baseline of a 756Pro2 that we couldn't even hear as it 
began to snow.  Then silence.  So, being highly experienced, we replaced 
it with another 756Pro2, and watched it die the same death.  Easiest way 
to do it externally is to solder a 50K or so resistor into a PL-259, 
screw it onto one arm of a coax T, put the antenna on the other arm and 
screw the T onto the radio.  You can use an RF choke instead of a 
resistor, however that can sometimes lead to parasitic resonances.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

**The original transcontinental railroad began in Sacramento.  The 
government subsidy to the railroad was higher for construction in the 
mountains.  The terrain around Sacramento is very flat, and the 
foothills of the Sierra Nevada are a good 30 miles or more to the east. 
  A few miles NE of downtown is a golf course [flat], and there is [or 
was] a plaque on a rock that read, "The mountains begin here."