Icom IC-706MKIIG Reverse Swing

[broncoman529]

I have had my Icom IC-706MKIIG for about 5 months and I am getting reverse swing when I modulate. I was first told by some guys on the radio that this was happening. I put a power meter in line to verify that this was indeed happening and it is. I have a LDG AT-7000 Auto tuner in line and it still shows reverse swing on my meter. My radio does not show reverse swing on the display, Only on the meter in line. It was showing reverse swing with or without the new auto tuner in line. What could be the problem? My SWR's are perfect with or without the auto tuner or meter in line. I did buy the rig used, I noticed that it's output is about 55-60watts on AM with a whistle, From the factory it is supposed to max at 40watts. On SSB it hits almost 120watts with a whistle and is only supposed to do 100watts. Is it possible that the ALC was turned up to high causing the reverse swing? The station is not grounded as of yet since it is in a temporary location until the vertical gets up on the roof, Could this be the problem? Please let me know what you all think.

Thanks,

Larry T.

 

[CDX1220]

i too have that model and mine puts out dk 40w pep 110w am .on ssb 110-120 and thats from factory. i have notice that when i tried to turn the dk to about 5,10,20 i got backward swing but at dk 40 it swings forward to 110 pep i dont know but i guess it set to work with that dk at 40 .try it at 40 and lets see what happens hopes this helps. and i talk all over when i go am. which is not very often.

 

[broncoman529]

try it at 40 and lets see what happens

Are you talking about adjusting the power via the menu or the ALC inside the radio? No matter where I set the power via the menu (Low-High) I still get the backward swing result. Thanks for the reply

 

[W5LZ]

There really is a reason why they recommend only so much power on AM, usually because that's all the radio is capable of doing without there being some distortion. Sure, you can raise that dead-key, but it doesn't do you much good, does it. Put the thing back to the original settings. Also from the sound of it, that was done 'inside' the radio, not by menu option. If you don't have the equipment to do that adjusting with I'd recommend taking it to a reputable technician. It's better to set things too low, rather than too high. You will NOT be loosing anything useful. That applies to any solid state radio, not just to Icoms.
- 'Doc

 

[Beetle]

Unless you speak a language that actually involves whistling, don't use "a whistle" to determine a radio's output. It doesn't do anything useful, and it stresses the circuitry well beyond reasonable limits, although just briefly.

 

[SR385]

What is the ALC reading when you see this? I'm thinking you are hammering the rig with the mic gain and the ALC is folding back your power. If that is the case you will have a horrible signal going out.

A 100W radio on AM is to be set at 25W dead key, set the processor off and mic gain so there is _no_ ALC deflection. If you drive it harder than that, you will have a distorted signal.

For SSB, run the power all the way up and adjust the ALC via mic gain for about 1/3 to 2/3 of the range in deflection during your avg voice peaks during transmit.

 

[broncoman529]

Trust me, I did not go inside this radio at all. I bought my radio used. The ALC is set well within limits(No deflection whatsoever), I have the mic gain set at 6 with the processor off. I like nice super clean modulation and I am not a power fiend. I was not looking for peak power when whistling, It was just the easiest way to show reverse swing on the power meter. So do you guys think that I am getting reverse swing from whoever set the power in the radio to high? Please let me know and thanks for the replies.

 

[SR385]

Trust me, I did not go inside this radio at all. I bought my radio used. The ALC is set well within limits(No deflection whatsoever)

K, wasn't implying you did, was just making statements in general.

If you suspect someone maybe went inside and made adjustments or used the service menu to do the same (not sure where carrier drive level is set with your rig exactly). If you are comfortable doing so, I'd snag a service manual and go through the specs and get that thing tested/aligned to spec.

It's very hard on the finals with these rigs if they are driven too hard so you want to be sure that if you see 100W on the power meter, it really is doing that and not more...or if the ALC is showing minimal deflection, it really is set that way.

Most of those adjustments are simply done with a VOM at test points. However the boards are very tight so getting to the test points carefully is tricky.

 

[W5LZ]

broncoman529,
Yes, I think your radio is mis-adjusted. No idea who may have done that mis-adjusting, but someone did, I seriously doubt it came that way from the factory .
Good luck...
- 'Doc

 

[74IN]

I was not looking for peak power when whistling, It was just the easiest way to show reverse swing on the power meter

So it doesn't do it with voice?

 

[broncoman529]

I was looking to replicate the reverse power indication, Whistling was the easiest way to make it happen and yes it does do it with voice. I agree, I think the radio is mis adjusted myself. Any ideas? do you think the power may have been turned up inside the radio?

 

[74IN]

Open it and look.

The user manual gives "recommended" settings.

Just the top cover, I'm pretty sure.

 

[rfoverlord]

damn golden screwdrivers! messy up a already good radio

 

[dxhound]

OK, let me try to explain this simply. Most if not all modern solid state hf rigs use what is know as low level modulation for AM. The audio is applied to the driver only (some cases even the pre driver) and relies on the final amp to amplify the carrier and the intelligence (audio). The result of this(due to biasing and other properties) results in a signal that is not a TRUE AM signal. These rigs if adjusted very carefully can achieve "FWD swing" however, in most cases, the factory setting is set in a way that the duty cycle and amp draw will not ruin the amplifiers. What happens when you look at the signal on a scope, is the audio is actually being deducted from the carrier instead of being applied to it. This is why you see "back swing" In a high level modulated radio like todays cb's and exports, that would cause premature failure since it was no designed to do this. But in solid state HF rigs this is normal and will not hurt a thing. But like I said, with quiet a bit of tinkering you can achieve true AM(some rigs may never be able to achieve this.
I offer these tips for you to try, they worked on my 857D

First, lower the carrier to about 5 watts. (the reason is to leave plenty of headroom for the audio)
set everything to 50% (ALC, AM MIC Gain, any other setting affecting AM audio or filtering)
Turn of the speech proscessor!!!!! you dont need this!

With a normal speaking voice, check the signals output.
Now if it shows forward motion increase only the carrier by 5 watts and recheck signal.
Do this until fwd motion ceases(stop at 40w carrier, dont go any high than this)

Once you reach the point of no fwd motion, try adjusting the AM mic gain in either direction until you come to a point of maximum fwd movement(This setting will surprise you as my best result was at only 28% Mic gain.

Now adjust your ALC until you see even more fwd move ment

You will have fun going back and forth between these two settings and trying diff combos. The best thing is to have a friend on the RX end so he can tell you weather or not your audio is fuzzy or too weak(keep in mind its not a connex!!)

You will do alot of testing and probably start over and do diff configs a couple times.

Just write down each setting when you reach a desirable point so you can refer back to that setting. GL and most of all HAVE FUN!!

 

[dudmuck]

I suppose the reason radios like the cobra 25/29 and General Lee, etc. are "loud and proud" because they AM modulate using audio power amplifier to modulate the final RF power transistor.

HF ham rigs are primarily used as SSB radios, so I would expect them to be optimized for that use.

I think that low-level AM modulation could be considered "true AM", but the problem is that all amplification stages after the modulation must be linear, meaning not reaching into gain compression on the envelope peak of modulation. Some people might call that head room.

The advantage of high-level (or high-side if you prefer) that you talk about is that the RF amplifier stages before where the modulation is applied need only be class C and no linearity requirements. The drawback is the modulation must be applied with high audio power to the final stage, but you end up with better AM.

I offer these tips for you to try, they worked on my 857D

I am an owner of an 857d. And its moded to be capable of operating on 11 meters to make direct comparison with CB radios and General Lee.
I can say that the best settings for AM transmit are this:
1) Microphone "tone" button set to position 1 for english (2 is muffled for japanese).
2) PROC turned on to approx level 30. adjust a bit to your liking, not too much.
3) DSP microphone equalizer OFF, or maybe "Low Cut" on if you think it helps.
4) AM MIC gain: start at 50 and adjust up to your liking.

All this is explained in the ft857d owners manual.