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Author Topic: AM Nets -3875 East Coast Net  (Read 1627 times)
AI4QJ
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Posts: 3




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« on: February 14, 2012, 08:49:37 PM »

Has anyone ever tried using a modern rig like an FT-950 on AM in the 75 meter band? Actually there are a few people on 3875 and I tried to answer their call and they did get my call and location but said I was over-modulated and basically, if you don't sound 100% to these operators they will not talk to you. They absolutely refuse to help you improve your settings and seem to try to bring in new ops so they can have fun criticizing them. However, I didn't care as long as I could get some help with my settings. I waited until the net control from New Hampshire said 73 and closed the net, then called I CQ and this same control op comes back and says 'I barely say 73 and here we have someone calling CQ!' He then went on to criticize my modulation  I was so embarrassed to have been caught calling CQ on his private AM frequency (NOT). They seem to get QRM'ed quite a bit too and I can almost understand it as you reap what you sow (even if it is illegal). Anyway, I set my FT-950 to 100 watts out and 25 watts carrier. If I was over-modulating then it could have been my MD-100 mic gain set too high. It has been a long time since I tried AM (last time was 25 years ago on 27MHz). Do these newer rigs really produce a decent AM signal or must you use a boat anchor to really do AM? Any suggested settings would be appreciated. I also had an ameritron al80-b and the carrier power was about 300 watts. Suggestions would be highly appreciated. de ai4qj Cool
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KB4QAA
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Posts: 2259




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« Reply #1 on: February 14, 2012, 10:32:05 PM »

Sorry you feel slighted.  I regularly listen in that vicinity and I have never heard anyone rejected for using a "rice box" rigs.  Many of the modern rigs have excellent quality when properly adjusted.

One of the first things I was taught as a Novice was that if anyone ever says you have a major problem with your signal stop transmitting until it is fixed.  Don't even transmit to close.  *shrug*

In general terms here are things to look at:

-Read and follow the radio manual

-One thing often not understood is that AM uses about four (4) times the power of SSB.  Consequently you will probably find you manual says to limit power to perhaps 20w or 40W.

-Your first reaction when told you were over modulating should have been to reduce ALC as needed until you got a clean report.  If that was not a enough, reducing Mic Gain would be the next choice.  Of course Compression or Speech Processor should never be used.

-If you are serious about AM operation, then building signal sampler and using an O-scope will help keep things tamed.   In the mean time, get with an AM'er or technician in your area who can confirm the right settings for your radio.

There are plenty of resources on the net for AM.  
Good starting point:
 http://amfone.net/Amforum/index.php

Don't give up, and keep it clean!  Smiley  73, Bill
« Last Edit: February 14, 2012, 10:34:28 PM by KB4QAA » Logged
WB2WIK
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Posts: 20542




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« Reply #2 on: February 15, 2012, 08:52:21 AM »

The FT-950 and most modern DSP rigs can sound fine on AM if properly set up.

The guys on a net usually aren't going to take the time to help you do this; however try a different time when there isn't a net and one local might help.

I found with my Ten Tec stuff I have to drastically change every single TX setting (from SSB) when using AM.  Now that I've done it many times, it only takes a few seconds; but initially it took some experimenting with a second receiver in the shack (I used a 75A-4 with a 6 kHz "AM" filter and a set of headphones to listen to myself).

With my stuff, I have to change:

Power from 100W to 25W (carrier level).
Mike gain from 50 down to 25 (about half the mike gain).
TX bandwidth from 2.4 kHz or 2.7 kHz (used for SSB) up to 3.9 kHz for AM.
Compression level (speech processor) from 30% (SSB) to "OFF" for AM.

Each rig is different, but this is four setting changes I must make to sound good on AM.  The Ten Tec is capable of almost 100% modulation (on a scope it appears to hit 95% negative peak and 100% positive peak, using my optimized settings) on AM, but some rigs aren't.

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WA3SKN
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Posts: 5434




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« Reply #3 on: February 15, 2012, 12:18:14 PM »

Read the manual.
Old radios used class C and modulated in the final amplifier with a big audio amp.  New radios use amps in the linear mode and modulate at low levels.  Don't expect a clean signal at the 100 watt level... you are WAY over-modulating that poor FT950!
A simple diode and earphones will let you hear your AM signal.  Try transmitting into a dummy load while listening... then you will know what you sound like.

-Mike.
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