Topband: RX epiphany?

[Tom W8JI]

> In your opinion; given a receive antenna with negative gain, at what level 
> does the negative gain start to come into play? -25 dBi, -35 dBI ?

There are several variables to this.

Estimating from a model:

 At my house a ~ -25 dBi gain antenna system with a pattern like a good 
large 8-circle, around 13 dB directivity, is adequately below propagated 
noise with a receiver like any of my Yaesu's on 500Hz bandwidth.

Since noise power is proportional to bandwidth, half the filter BW has half 
the wideband noise power. Signal power is the same as long as it is inside 
the filter bandwidth changes.  A very narrow filter on a quiet night needs 
more sensitivity than SSB bandwidth. Some people can filter in their heads, 
too. I've found I'm better than many and worse than some others for that.

I split four ways, which is about 6-7 dB loss, and that makes the system 
sound pretty dead, so I'd say here what models to be a -25 dBi antenna works 
with several dB headroom at 500 Hz BW on quiet nights with sensitive 
receivers.

I've found some receivers, because the manufacturer assumes everyone 
receives on a transmit antenna or is in the city, do not have enough gain.

It would be very interesting to see what others find, if they have looked at 
it.

http://www.w8ji.com/receiving.htm

73 Tom