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FT-900 Negative Swing on AM ??

TonyV225

W9WDX Amateur Radio Club Member
Apr 18, 2005
5,824
314
143
Wisconsin
I threw the towel in on this one to like I was saying to him earlier today I have seen this but without the radio infront of me IM LOST!!
 

jwhawg

Member
Oct 2, 2009
25
0
11
Yes it does swing backwards on a bird peak reader. And every other I have tried. I was also hoping that it was just a meter action, or reaction, but I send a negatively swinging signal to other receiving radios. Staions say I have great audio, but swing from say s-9 back to s-7 or whatever.
 

jwhawg

Member
Oct 2, 2009
25
0
11
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.

Was wondering if you had transmitted on am with your 746? Just curious as to seeing if it also swings backward to receiving stations?
 

Alcahuete

Member
Oct 27, 2009
2
0
11
43
California
Very interesting...new member and happened to find this site after a Yahoo search for something totally unrelated. What do you know, this thread was right near the top.

I have had a very similar issue with my radio (FT-900AT) for quite a few years. The funny thing is that this happened right after a visit to the Yaesu factory (in Cerritos) for some warranty work. The radio for whatever reason blew a resistor and capacitor (I believe, though I don't have the exact report on-hand right now), which ultimately ended up with nothing but RF and no audio at all. After getting the radio back, it appeared to be backswinging on AM as well.

I haven't tested it side-by-side with another radio in years, so I don't remember if it was actually swinging backwards on another radio's S-Meter. The ammeter on my power supply shows a good drop in amperage when using the radio, from deadkey to modulation, but after hooking it up to a watt meter, I got some interesting results. My peak-reading watt meter showed that it would deadkey around 40 watts and swing up to about 130 watts when talking. The radio itself puts out about 130 watts on all other modes as well.

So I guess I'll sit it side-by-side with another radio one of these days and see what the S-meter is saying.

Interesting thread. Nice to finally come across a discussion on this. :)
 
Last edited:

jwhawg

Member
Oct 2, 2009
25
0
11
Well, Now we might be getting somewhere! The very same rig (FT900AT). Please, if you can, take some time and see if it really is sending a backward swinging signal to another radio. Post what you find. And thanks a million!
73 Joe K0TRT
jwhawg
 

jwhawg

Member
Oct 2, 2009
25
0
11
I'm going to be out of town next week so I'm taking the radio over to my local tech. See what he says. I'll post. Not sure if the Welcome new comer was for me or the other gent, but thanks anyway hihi
73 Joe K0TRT
jwhawg
 

dxhound

Active Member
Nov 17, 2006
783
58
38
Sounds like a classic case of low level modulation being overmodulated. Does the radio have an ALC menu function? Sounds like the ALC is detecting and overmodulated signal and is attacking/overshooting your audio. Try adjusting the ALC and play with diff. mike gain settings. None of these low level modulated solid state rigs use true AM. They actually detract the intelegence from the carrier instead of add to it. An oscilloscope will show you this. In other words if you look at the carrier on a scope and it shows 10v pkpk. The modulated signal peaks will still be 10v pkpk but the "lows" will be 2.5v pkpk(asumeing a 4to1 100% modulated signal) So what you have efectively done is lower your avg output when the inteligence is applied.

Now that said, there is a way around this. Again by adjusting these basic radio settings
ALC
Mic gain
Carrier power level

There other setting that you could look into also(not sure that your rig has these opotoins)

Am freq roll off- this adjusts the transmitted audio response giving base or trebble sound

AM mic gain- this is independent of total mic gain

Using these settings I have achieved "true"(I use this term loosely here) 100% modulated AM on both my yaesu ft857 and my old Icom 746 Both about 20 watt carrier with around 85-100 watt peaks. And these peaks are seen on my LP-100A watt meter. My AVG talk power is about 45-60 watts depending on mic and drive.

I hope this helps. The best thing to do is get a watt meter and dummy load and just play. A scope would even be better
 
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jazzsinger

Bullshit Buster
Jul 3, 2008
1,750
333
93
United Kingdom
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.

It shouldn't put out more than 26w carrier,chances are someone has increased the internal carrier preset vr1017 to get more carrier power,that would be the first thing i'd check.with carrier that high there is insufficient audio to modulate the carrier hence downward modulation/negative carrier shift.

its also possible there is improper coupling between rf stages or between final and antenna,proper alignment is the cure for that,poor voltage regulation within the radio or inadequate or poorly regulated psu is another thing that can cause downward modulation.

as the radio is putting out 130w on other modes chances are they are misaligned too,as it should only be doing 100w,it reeks of a cb'er or amateur with lack of knowledge trying to screw extra wattage from it with no concept of the consequences of doing so,if radio is opened for wideband tx it was almost definately a cb'er.

A good read at this http://www.download.n7tgb.net/yaesu/FT900/FT-900_tech_supp.pdf may help you solve the problem and return the radio back to manufacturers spec.
 

jazzsinger

Bullshit Buster
Jul 3, 2008
1,750
333
93
United Kingdom
Using these settings I have achieved "true"(I use this term loosely here) 100% modulated AM on both my yaesu ft857 and my old Icom 746 Both about 20 watt carrier with around 85-100 watt peaks. And these peaks are seen on my LP-100A watt meter. My AVG talk power is about 45-60 watts depending on mic and drive.

for 100% modulation at 20w carrier you should be seeing peaks around 78-80w,with 85-100w peaks you are seeing overmodulation.
 

MisterFatty

Poppin Fresh!
Aug 1, 2008
698
33
38
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.


My brand new Kenwood TS-480SAT does the same, On the 6 different watt meters I have, which range from my El-Cheapo Midland vintage, to my Bird 4430 with Peak reading Kit. Best I can tell it sounds ok. As for signal strength on receive it seems to do the same. It also draws LESS current on voice peaks. Now this I'm sure can be minimized, and probably doesn't sound too bad, however, it sure as hell isn't going to sound better then my Old EFJ Valiant as some on the forums seem to think.

BTW, It makes absolutely no difference, 5 watt minimum, or 25 watt max, Antenna, Dummy Load, or band, does the same thing, Now SSB, thats a different story...

One of these days I'll get into the service menu and try some different settings, from what I've read it will help some, just not a priority.
 

W5LZ

Crotchety Old Bastard
Apr 8, 2005
6,832
820
173
Oklahoma
What's the most common reason for 'backwards swing' on any radio in the AM mode? It's the same with this '900, or any other radio, you've reached a limit on modulation basically. Any radio is going to have a maximum in what it can produce, all of them. To get any more than that you will have to make changes in the amplifying devices that produce that modulation.
For instance. Most radios (ham or other wise) advertise that they will do so much total power. That's usually in a CW mode. When you change to AM mode, that power is no longer just a carrier or 'dead key' supplier, it splits between carrier and modulation. The total amount of power stays the same (call it a 100 watts). Half of that 100 watts is now producing the modulation, not carrier. Because of how the duty cycle works with the various modes, the total power output of a typical 100 watt radio is not a 1/4th of what it's total power level is. 100 watts is still being generated, but it is sent to different 'modules' in that radio, half here, half there. That deals with what you can reasonably expect to keep things in a reasonable shape to last more than just a few minutes. Absolutely normal limits for a manufacturer who want's to stay in business and sell his product.
So if it amounts to you wanting more than the advertised power per particular mode, get a radio capable of doing it, not over stress one that isn't. Or, use an amplifier.
Why would some 'older' radios do more AM than the newer ones? Because that's what they were designed for to start with. If you got a pocket that'll hold 2 pound of rocks and you want to carry 5 pounds of rocks, you'd better have more than just one pocket, right? Same difference.
- 'Doc

If it'll only do 20 watts AM instead of the advertised 25 watts... do you really think anyone is going to be able to tell the difference? Really?
 

Shockwave

Sr. Member
Sep 19, 2009
3,778
3,269
273
You are experiencing the effects of modern low level IF modulation. The fact the radio swings backwards even at a 5 watt carrier tells me this is not ALC related. When looking at the schematics of newer radios it seems to me they have gone out of their way to cripple AM modulation. If would be so much easier to modulate an RF stage an obtain perfect results rather then using the balanced modulator and sending the audio through the IF strip.

To make a long story short I think you'll find the radio is working fine according to factory specs. It's just not designed to perform well on AM. I gave up on modifying the IF strips in these radios years ago because the results are no where near as good as abandoning the balanced modulator on AM and going deeper down the RF strip to apply modulation.

The radio can be modified to swing forward but I have to tell you that very few technicians should be trusted with this job. I've seen too many butcher jobs done in the past. The concept is easy, the application is harder to do in a clean manner. Yaesu will never do this job for you. The best way to go is to remove the audio from the balanced modulator and find an appropriate RF stage to apply this modulation.

The complex part is finding the right RF stage to modulate and then making the modification switch in on AM and out for the other modes. Some early IF modulated radios like the FT-901DM can be modified to sound good through the balanced modulator. Most of the newer radios fail miserably here in terms of peak AM power.
 
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jwhawg

Member
Oct 2, 2009
25
0
11
What's the most common reason for 'backwards swing' on any radio in the AM mode? It's the same with this '900, or any other radio, you've reached a limit on modulation basically. Any radio is going to have a maximum in what it can produce, all of them. To get any more than that you will have to make changes in the amplifying devices that produce that modulation.
For instance. Most radios (ham or other wise) advertise that they will do so much total power. That's usually in a CW mode. When you change to AM mode, that power is no longer just a carrier or 'dead key' supplier, it splits between carrier and modulation. The total amount of power stays the same (call it a 100 watts). Half of that 100 watts is now producing the modulation, not carrier. Because of how the duty cycle works with the various modes, the total power output of a typical 100 watt radio is not a 1/4th of what it's total power level is. 100 watts is still being generated, but it is sent to different 'modules' in that radio, half here, half there. That deals with what you can reasonably expect to keep things in a reasonable shape to last more than just a few minutes. Absolutely normal limits for a manufacturer who want's to stay in business and sell his product.
So if it amounts to you wanting more than the advertised power per particular mode, get a radio capable of doing it, not over stress one that isn't. Or, use an amplifier.
Why would some 'older' radios do more AM than the newer ones? Because that's what they were designed for to start with. If you got a pocket that'll hold 2 pound of rocks and you want to carry 5 pounds of rocks, you'd better have more than just one pocket, right? Same difference.
- 'Doc

If it'll only do 20 watts AM instead of the advertised 25 watts... do you really think anyone is going to be able to tell the difference? Really?

Not quite sure what you are getting at???? Are you saying that I did something, anything to the inside of my radio?? If so where are you getting that from??? I have done noting to the inside of my radio. Nothing! So keep your opinions of how or why my radio is the way that it is. Have you ever bought a used rig??? Who knows what has been done to them and by whom. I dont need your comments or your opinions. This has been positive until now. No body is trying to get any more POWER out of the thing than needs be. READ BEFORE YOU WRITE.
 

jwhawg

Member
Oct 2, 2009
25
0
11
You are experiencing the effects of modern low level IF modulation. The fact the radio swings backwards even at a 5 watt carrier tells me this is not ALC related. When looking at the schematics of newer radios it seems to me they have gone out of their way to cripple AM modulation. If would be so much easier to modulate an RF stage an obtain perfect results rather then using the balanced modulator and sending the audio through the IF strip.

To make a long story short I think you'll find the radio is working fine according to factory specs. It's just not designed to perform well on AM. I gave up on modifying the IF strips in these radios years ago because the results are no where near as good as abandoning the balanced modulator on AM and going deeper down the RF strip to apply modulation.

The radio can be modified to swing forward but I have to tell you that very few technicians should be trusted with this job. I've seen too many butcher jobs done in the past. The concept is easy, the application is harder to do in a clean manner. Yaesu will never do this job for you. The best way to go is to remove the audio from the balanced modulator and find an appropriate RF stage to apply this modulation.

The complex part is finding the right RF stage to modulate and then making the modification switch in on AM and out for the other modes. Some early IF modulated radios like the FT-901DM can be modified to sound good through the balanced modulator. Most of the newer radios fail miserably here in terms of peak AM power.

Thanks Shokwave! I think we may find out why these rigs do this. I belive that they may do it right out of the box, new. I don't know. I'm just trying to find as much positive info as I can about this rig and any others that may do it. We may find a common factor and a final remidy. I'll post what I find, hope you will too!! That's how we learn.
Thanks so much again !!
Joe K0TRT
jwhawg
 

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