On Thursday, January 23, 2014 7:16:54 PM UTC-6, Ralph Mowery wrote:
wrote in message

...



It all depends what freq, type of operation, etc.. But for general

skywave HF, even a fairly inefficient antenna can be quite fine

for receiving in many cases. The level may drop with the inefficient

antenna, but assuming the same basic pattern, the s/n ratio should be

pretty much the same. If you have enough antenna to increase the

background noise when connecting the antenna to the radio, it should

be fine for general gov use.





I always hear that, but it doesn't seem to be that way for me.



I have an off center fed antenna (about 125 feet long) mostly flat at 50

feet. Also a 3 element triband at 60 feet. Both fed by low loss rg8 type

coax. On some of the weaker signals on 20 meters I don't hear signals on

the OCF that are good copy on the beam. Also an 80 meter dipole at the 45

foot level at right angles to the 80 meter antenna will not hear what the

beam does in some cases. That is in a relative quiet location as far as

noise goes. The receive is an Icom 746pro.


That would almost surely be more pattern related than efficiency.
And the beam has gain in the direction it's pointing.
If you took any one of those antennas on it's own and lowered
the efficiency by adding resistance at the feed, a more lossy
feed line, or added tuner loss, or even just used an attenuator,
the signal level will vary, but the s/n ratio should change very
little. Both the noise and desired signals are going to be reduced
equally. Only when you get to the point where hooking up the antenna
and not noticing a noise increase at all, are you starting to really
have a problem with reception due to lower system efficiency.