The AM Forum

The phone portion of the 3.5-4.0 mc/s band has historically been known as "75 metres" because it butt-ends against the very top frequency in the band.  To convert frequency to wavelength, divide the frequency in megacycles/second or megaHertz if you prefer, into 300.  We thus see that 4.0 mc/s = 75.0 m exactl/y.

Before 1932, the phone allocation for this band was 3500-3550 kc/s.  3500 kc/s = 85.71428... metres.  I recall seeing in old radio publications, the phone band called "85 metres."

So where does "75m" end and "80m" begin?

The exact midpoint of the band, 3750 kc/s = 80.0000 m. exactly.


Here are some frequency-to-wavelength conversions:

4000 kc/s = 75.00 m

3950          75.94 m

3900          76.92 m

3885          77.22 m

3880          77.31 m

3825          78.43 m

3800          78.94 m

3750          80.00 m

3700          81.08 m

3685          81.41 m

3650          82.19 m

3610          83.10 m

3600          83.33 m

3550          84.50 m

3530          84.98 m, ~ 85.0 m

3500          85.71 m


I recall as a SWL in the 50's, some international broadcasters, including the BBC,  still gave their channel locations in wavelength instead of frequency.  When AM broadcasting was first established sometime about 1922, every station in the US was assigned one frequency, 833 kc/s, or 360 metres.  Eventually, amateurs found themselves "relegated" to wavelengths of 200m and down, or 1500 kc/s and above.

So, when should we call "CQ 75,"  and when should we should it be "CQ 80"?

CQ 77

The ARRRL, is using the split between cw, and phone portions as the breaking point between 80 and 75.......

Your breakdown says it all though.....



As far as when you should call "CQ 75", or "CQ 80"....

Well, I guess that's up to you.....

I haven't seen a good reason to have to announce what band you're on, unless you're worried about your harmonics..... and want to be sure someone will answer you on the right band.........

But, maybe I'm missing something...... after all, I only had to pass a 13wpm code test ;D
(Is that "extra-light", or "extra-ultra-light" ?) :D

K4KYV asked:
_______________________________________________________________
"So, when should we call "CQ 75,"  and when should we should it be "CQ 80"?"
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I pretty much follow the old frequencies, Don, which also follows the 4.00=75 meters and 3.750=80 meters formula.

When I am calling anywhere between 3.750 and 4.00 MHz, I call "CQ - 75"  And when I am calling anywhere between 3.750 and 3.600 I call CQ - 80. 

Now somebody's bound to ask, "Well, what about when you're exactly on 3.750?"  That's 80 meters, obviously.  But if I'm on 3.751, that's where 75 meters begins.  Don't even ask about 3.7501 - 3.7509! ???

vH

P.S  Nice job, Don, in laying out the MHz to meters conversion table.  That's very handy, and saves wear and tear on the calculator. :D

If you call CQ and some idiot comes back and tells you to get off his net frequency it might be 75.
If you call CQ and some Canadian idiot tells you to get off his net frequency then it is 80.

I'm more concerned with whether it's meters or metres.

I think it's an anachronism to call CQ 75 or any other band. It dates to the time when all stations were crystal controlled. So, although you were calling CQ on a particular frequency, you would listen across the band for a reply. The entire band was tuned because the station returning to your CQ wasn't likely to have a crystal at the same freq as yours.

I have 12 meters mounted on the front panel of my transmitter.  4000 kc/s=75.0 metres.

hmm,
     hadn't thought about it, but herbs ideas make the most sense  I guess.
I havn't called CQ down at 3685, only back up the old 3885. My run on
75 is, listle on 3885 & call cq there, if nothing. take a peek  on 3685, then tune
dx window. worked some am last night, and then worked european dx
after that. just great condx.   Not sure why we call "cq 75" or 80, but
I've heard guys on 75 calling "cq 40" or other such mistakes, forgetting
where they are ;;

Some of the old euro radios had the scale marked in meters as well.  This one was marked in meters and frequency but the frequency scale was "backwards", i.e. it increased in frequency from right to left:

(click on attachment name for higher res)

Don, I'll see you on 81 meters!
By the way, we still have quite a few who are reluctant to move from 3885. Remember to S P R E A D out and use those open frenquecies... or should I say wavelength?

A friend forwarded me this e-mail.  Names and callsigns will remain undisclosed.


You would be surprised how many SSB ops monitor the AM boards just to keep
track of our off-the-air comments.  I  have heard remarks over the air
about the content of messages posted on this board.  This dildo obviously thinks that we all
listen to AM with our receivers in the LSB mode, or else he is one of the
Extra-Lite crowd too ignorant to figure out that with the receiver in AM
mode you will hear the quacking above and below the carrier frequency.

My thoughts exactly. Anyone who thinks the average AMer can't hear signals 4 kc off their frequency is obviously an idiot. Probably a sleeper slopbucket. It's a well known fact they are all idiots.

He also shows his hate filled narrow minded thinking with the stereotyping "AM only til I die" crowd. Who would this be?

Another loser heard from.

Check out the AM Reflector.  The title of the thread is "Frequencies."