Antenna Noise on 6m

[VK3OE]

I have heard many discussions about noise on 6m. In many cases it is claimed that the "noise is very low today" but I do not know what that means.

It seems to me that it is rather easy to measure the antenna noise level and thus when it is discussed a level in dB increase above a 50ohm load could be referenced, it is very easy to do.

There are of course a few assumptions, first is that the noise figure of all rigs is the same (not true), second that there is no intermod from other strong nearby sources into any receiver and third, and that the antenna input impedance is close to that of the reference load in every case. And yes, I know all about noise figure and all the other complexities but I thought a simple measure would at least be an indication.

So, the concept of the simple antenna noise measurement is to connect a 50ohm load, then connect the antenna and see what the difference is in dB as an estimate of the antenna noise. Of course if a receiver has a very poor noise figure then the antenna noise increase will be small and the system looks as if it is very good when in fact the opposite is the case.

As a starter, on 6m on a good day at the remote site VK3OER, the noise increase is 6dB over a 50 ohm load with preamp on and 4dB increase without the preamp. On a bad day it can be up to 15dB, mostly from electrical sources (IC7000 with and without preamp).
At my home station VK3OE on a good day the noise increase is 12dB over a 50 ohm load with preamp on and 6dB increase without the preamp, on a bad day well.. 30 to 50dB is common, oh well. (IC756PIII with and without preamp).

So how much increase in noise does your antenna give over a 50ohm load.

And yes I know it is an estimate and depends on many things but,,, have a go.

Andrew
VK3OE/VK3OER

[VK6ADF]

In my case I say 6m is noisey because of powerline noise indicating around a constant S7 to 9. Not the noise you mean I guess.

[VK3AUU]

It is also instructive to point the antenna in different directions and observe the results, as well as monitoring the noise in the direction of the rising or setting sun to get an idea of at what elevation your gain peak is.

David