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The Five Hurdles - K1JJ




 
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« on: June 04, 2005, 01:36:20 PM »

The Five Hurdles

 Tom K1JJ.
I often hear new AMers asking " What do I need to put together an AM station that is considered "advanced" "?
 
IE, "How can I cut right to the chase and be a strapper right away"?   :-)
 
Just what goals or systems do I need in place to fully appreciate what fidelity AM has to offer for both transmitting and receiving?  
 
How do I test my gear to insure it's doing just that?
 
And,  how can I give out accurate audio reports to help other newcomers?
 
Here's one ham's opinion as to  where to focus your energy to arrive at these goals.  This and the next series of articles address these and other important questions.
 
 


1) I feel the first thing any AMer (worth his salt)should do is set up a decent, ~8-12kc wide-band receiver. It's MANDATORY to pick off the audio from the detector and drive an external >20watt hi-fi amplifier with big, good speakers....four speakers mounted on the four ceiling /wall corners. Audio sweep the complete RX system from antenna to 8 ohm audio output to be sure it is clean and really goes 20-10,000 hz. Those I.F.'s can fool you sometimes.

So many times I've visted shacks where guys think they have good rx audio with a "stock" or even modified receiver...but are really missing the deep lows and high end - not to mention the inherent distortion generated by most receiver audio sections.

Until one has heard the likes of WA1QIX, K1KW, W2INR, WA1HLR, KG2IR,  AA3WH and others in ass kicking loud "FM Radio Quality" surround sound, it's hard to accept what I'm saying. It's truly amazing how good these guys sound when they rumble the room and you can hear their subtle breathing, (panting) sighs and the clean high frequency harmonics of their voices.

The receiver detector into a hi-fi amplifier /big speaker system is the only way to get this sound.

Turn up your high end FM stereo on a mellow radio announcer sometime to see what I'm talking about -these AMers sound even better.

Listening to fine Hi-Fi RX audio reminds you of why you are in this AM game in the first place - and motivates.


2) The next challenge is to get your AM transmitter to audio sweep cleanly (VERY CLEANLY) from say 40hz- 7kc or higher. On the scope. This in itself is a challenge.

Once this is accomplished, THEN add the EQ's, processors, expensive mics, etc. Without this transparent transmitter audio, all this stuff is just fooling yourself with trying to match a peaky transmitter with a mic/system that will try to compensate...along with distortion generated by boosting areas that are lacking, non linearities, etc. Cat chasing it's tail... endless asking for reports on the air.



3) Lastly, one needs a good recording system that comes off the detector of the wide band receiver and can play back through your flat transmitter in a transparent manner. This is the best, most informative audio report/service you can give anyone. Nothing else has to be said once it is played....guys react immediately to what they must do once it is heard. Most will then adjust their EQ/processing to satisfy themselves, not the infinite amount of opinions of others who have their own agendas as to what kind of audio THEY prefer or what YOU should sound like.

IE, ask Irb how you sound, then ask Nick...two totally different opinions...and everyone else is gonna say differently too! :-) A clean tape playback is the best way to dial things in to suit your own taste!

IE, ask for a tape, not an opinion when adjusting your rig. And remember, you need a hi-fi RX system as described above to really hear what is being played back to you!


4) Dipole at 50' for 75M.

5) At least 250 watts of carrier and a quiet room background. Little or no blower noise.

 
Tom - K1JJ
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