FT-900 Negative Swing on AM ??

[jwhawg]

Hi,
Could anyonr tell me about negative swing on AM, and if anyone has remedied that situation. I know the more modern rigs have really NO place on am. But I have a mic that sounds good on am as far as good audio signal reports go, and have an amplifier. But needless to say the amp doesn't work properly with a reversely swinging radio. It swings in reverse at any power level and with any audio adjustment. Any ideas would be sweet !!

Thanks in advance
Joe K0TRT
jwhawg

 

[TonyV225]

How do you have it set on the radio settings?? I know the older radio owners manuals said 25 watt carrier and adjust mic gain until you see the neddle on radio meter just start to move while you speak into the microphone.

 

[jwhawg]

well that's pretty much what the manual says about setting up to transmit on am. But like I said, it really doesn't have any affect on the negative swing. Any position and combination of settings.

 

[TonyV225]

Hmmm?? and you have good SWR?

 

[jwhawg]

Yep. 1.2 to 1 on most of my antennas. But here is something..... This rig puts out a heck of a lot more that 25 watts on am. Somewhere around 40 watts. I think I'm onto something. This thing is probably "swamping" the audio.

 

[TonyV225]

It will swing forward ofcourse but you should put no more than 25 watts at dead key no audio Id put less say between 10 and 20 Watts. Try 10-15 watts deadkey and adjust that mic gain so it just tickles the radio meter as far as movement on output reading I am thinking this is gonna help. You have to remember there is crazy audio in these HF rigs and they are very very touchy.

 

[jwhawg]

It puts out 40watts dead key with NO audio input what so ever. Any audio input at all, no matter how minute will cause a reverse swing on any watt meter I have tried. My swamping theory is wrong because even with the rf power turned all the way down (5watts) it still does it. It does it with the stock mic hooked up to it. Although it has very little audio. ??

 

[TonyV225]

Ok so it shows 40 watts deadkey no matter where you adjust the variable power??

 

[jwhawg]

No. It puts out 40w with the rf power up all the way. I think it's only suposed to do only 25w on am, rf power adjustment all the way up. I can adjust it down to 25-30w, but that's with thr rf power at about half. On side band it does it's rated 85-100w. But the fact remains, even with power ADJUSTED back to rated power for am, I still get neg swing.

 

[TonyV225]

Ive had a few older radios that did way more out than 25 on dead key with the power all the way up but I just adjusted them to 15 - 20 watts and adjusted the mic gain. To much audio is going to make it swing backwards but there could be another underlying problem one of the other guys may interject here this afternoon with more ideas.

 

[jwhawg]

Well thanks for going over it with me. Sometimes another brain involved is enough to figure out most stuff. I hope this problem looks familliar to someone.
I'll keep trying. May need to find an old BA for am I guess. Anyway, have a good day and 73,
Joe K0TRT
jwhawg

 

[TonyV225]

Thats A OK thats what were all here for but now that you got me thinking and curious Ill have to watch because this also has me stumped and its worse when you dont have the radio infront of you if you see what Im saying. 73's

 

[jwhawg]

I know what you mean Tony and thanks again. I'll let you know what I find.
Joe

 

[Bionic Chicken]

If you use an external "peak" reading wattmeter does it still show to be backing up? On some radios I have had to play with the mike gain and compressor (if it had one) in order to get any forward movement out of it. Like it has been already stated most of the time if you lower the dead key to 10 to 15 watts they would move forward if only a little bit. Some of them can be a PITA to get set right but once you do...............

 

[Moleculo]

My Bird43P Peak reading meter always shows backward deflection on my Icom 746 Pro. I have never figured out why it does this. The active peak reading meter in my Ameritron tuner does not show this. My only guess is that some combination of mic, rig, and other audio gear causes the phase to be negative and somehow the meter reacts to this. Keep in mind that I have no idea whether this could occur...it's purely speculation on my part.