Good radio call is polite, precise, concise, and informative.  Boulder
frequency is crowded, hence good discipline is crucial!  Make sure you
know what you want to say.  That is, prepare your message in your mind
before you say it.  Make sure that you don't talk over someone already
transmitting.  Press the transmit button just before speaking.  If you
hear someone talking when you release PTT button, you can be sure that
they talked over you, and you should retransmit your message.

The standard transmission format is:

<who it is directed to>
<who am I>
<where am I>
<message body>
<who it is directed to>

A typical broadcast call (e.g., entering-glider-pattern) would be:

Boulder Traffic
Glider 9-6-3
is midfield
for left downwind glider strip 0-8
Boulder Traffic

That is, message body is announcing your intentions.

When turning base, it is a good idea to announce that as well:

Boulder Traffic
Glider 9-6-3
is on downwind
turning base for 0-8 dirt
Boulder Traffic

Use "glider strip 0-8" if you are landing on tarmac, and "0-8 grass"
or "0-8 dirt" if landing between tarmac and the main runway, that way
it is unambiguous.  You can also use "0-8 left" for tarmac, and
conversely "2-6 right".

If you want to direct your message to someone specific, instead of
"Boulder Traffic" use the aircraft's call number if you know it (from
his earlier message), or simply "yellow aircraft on downwind".

Another example --- you see someone flying power downwind while you
are on the glider downwind, and you want to make sure that he sees
you:

Red airplane on downwind
this is glider 9-6-3
on downwind
Do you see glider on your 9 o'clock same altitude?

Another example --- you are coming back from a flight and you want to
get wx check:

Boulder Unicom
This is glider 9-6-3
4 miles west of field at 8-thousand 5-hundred
(can I get) wind check please
Boulder Unicom

You may abbreviate the message and skip parts that are not relevant or
go without saying in order to keep it concise.  Obviously, if you are
on tow talking to the towplane that's towing, you don't need to
include your position.

For example --- you are on tow and want to tell towplane that you are
about to switch frequency (you would do this when you are 4-5mi out
from the field, at 8kft or more).

0-8-L
this is 9-6-3
switching to 23-3

when you switch:

0-8-L
9-6-3
is on 23-3

To make the towplane turn:

0-8-L
this is 9-6-3
please turn towards the cloud at 2 o'clock

To let him know that you are off:

0-8-L
9-6-3
is off at 8-thousand 3-hundred

To acknowledge a message that needs no other response other than the
acknowledgement, you can simply double-click PTT.  That way you don't
clutter the frequency.  For example, as a result of 08L acknowledging
your off-tow message you may hear two clicks.

Some useful phrases:
Say again?: I missed most/all of the message, please repeat it.
Negative: Standard phraseology for NO.
Affirm: Standard phraseology for YES.

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