This is the SATERN Website of Concord, CA.

Standing Waves

and how they apply to 2m Ham Radio.

When you look at the Ripple Tank pictures in the above page (Training Aids 1), you might
think, "gee, that is a nifty picture". (In my generation we used words like 'gee' and 'nifty'.
But you get the picture.) There is one showing a source whose radiation goes thru an aperture
with two openings. On the other side of the aperture is a pattern of stronger waves and weaker waves.
These are called 'standing waves', and they consist of minima and maxima from interference between
the various sources at the aperture. This un-animated picture is replicated here.

What can we learn from this? If the radiation pattern really consists of minima and maxima and this
is a static pattern (does not change with time), then when you pass thru this pattern as you listen to
a station, the reception will have changing S/N (signal to noise).

Now suppose that the signal source is the repeater on Mt Diablo, and you are traveling between many
big buildings within downtown Concord. Sure, the signal from the repeater is clean and spherical.
But as the single-source signal travels to the downtown Concord area, it is reflected from surrounding
hills and office buildings. This will result in a complicated pattern of minima and maxima. Again, if
the surrounding air is not changing, then this pattern will be static. Look at the animated GIF below.

Then take this quiz:
When the red auto comes to a stop, will his S/N be high or low?

When you travel thru a pattern of standing waves, you will experience changing S/N values. If the
communication is important to you, then you will probably realize what is happening and have the mind
to stop where there is a S/N maximum and listen.

And of course the reverse also happens. When you are transmitting to that repeater, the same min/max
pattern influences the signal from your radio to the repeater with exactly the same results. As long as
you are moving while transmitting, you cannot hear the difference in S/N. But all the people receiving
this signal can. And when the control operator tries to hear your callsign, it comes out as words cut out
with lots of hisssss.

Yes, during the Monday night 2m Network, anyone who is moving within standing wave patterns will not get
thru with a 5/9 report. We hear this often for a person on the road. The solution is to stop when you hear
a good S/N from the repeater. Then wait until it is your turn to transmit. When it is your turn, you will
transmit to the repeater with a 'loud and clear' signal that does not change with time.