[Antennas] Receive vs Transmit

[R E Lay (W9DMK)]

On Sunday 16 February 2003 14:03, DJED1@aol.com wrote:
> I think there are two reasons why receiving with untuned antennas is not as
> much of an issue:  First, as you point out, many older receivers have an
> antenna trimmer which will cancel out at least part of the mismatch between
> antenna and receiver.  Second,  your sensitivity, especially on the lower
> bands, is limited by external noise.  So if I have a "broadband" antenna
> with 10 dB of loss, it will not affect my reception provided the external
> noise is at least 10 dB above receiver noise floor.  (My experience at my
> suburban location is that I've got at least 10 dB above receiver noise up
> through 20 meters).  The S meter will be 10 dB lower than with a good
> antenna, but the signal to noise is still about the same.  On transmit,
> however, you've got to exceed the external noise at the other guy's
> location, so if you lose 10 dB, he may not be able to hear you.


Dear Ed,

Your explanation makes a lot of sense to me - TNX
Let's see if I can summarize it. 
1) No one seems to suggest that in the HF region the match makes any 
noticeable difference on receive.
2) Everyone seems to agree that the noise and signal  coming in through the 
antenna are usually so dominant w/res to the receiver's noise floor that we 
don't care about the receiver's internal noise. 

That leaves antenna directivity and efficiency as the primary concerns, and 
efficiency is probably inconsequential because of (2) above. 

So, unless you are willing to put up a receiving antenna that has enough 
directivity to give several dB of advantage, a 20 foot length of wire tied to 
the antenna terminal is as good as you need for receiving, and the reason for 
this is that it takes a tremendous amount of improvement applied to a simple 
antenna to improve the S/N on reception. Have I got it?

-- 
73 de W9DMK ( Bob Lay ) in Dahlgren, VA
w9dmk@crosslink.net
http://www.qsl.net/w9dmk