Yaesu FT-897 AM

[Quiksilver]

Any Yaesu FT-897 users out there? Occasionally, I would like to talk to the on AM. Maybe I have my settings wrong. I seem to get better reports with the stock mic –vs- the new Heil GM-5. I do more SSB, but occasionally operate on AM. I was getting “off-freq.” / “warble” reports on AM. I have done some hidden menu adjustments per an 897 forum, which seemed to help. Maybe it was just the operator on the other side that was “off-freq.” Seems to be odd for an “off-freq” report on AM.
Or do I just need to get a real AM rig for AM operation???????
Thoughts??

 

[Captain Kilowatt]

Nothing wrong with the stock microphone. I run the FT-857 which is the same radio in a different box meant more for mobile use. I have done the service menue changes and have had good reports on AM. Do NOT run the processor or just run VERY little if you do, run no more than 20-25 watts of carrier and make sure the ALC just starts to light up the first meter segment and it should sound pretty decent. I will admit that without the changes to the service menu it sounds like crap on AM.

 

[Quiksilver]

Capt.
I followed your "897 AM" post. Here's my settings:

Thanks for the info. Adjustments went fine. My setting are: AM-CAR-LEVEL 115 AM 21.000.00. And carrier was metered right at 25W.

 

[Moleculo]

What do you have the speech processor set to? My guess is that it's too high. I have both that mic and the radio, although I don't use AM much. What are the service menu changes that you guys made?

 

[Captain Kilowatt]

I made a post somewhere here on the forum about accessing the service menue to change the AM mode ALC. I can't find it right now but I just got off a night shift and am lucky to find the keyboard. Here is a cut and paste from one of my info files.

"To get a decent AM modulation waveform set up the rig for TX into a dummy load with an inline wattmeter. The watt meter does not need to be a peak reading type.
Set up for AM transmit on the band of intrest.
Set the METER ATX menu item to ALC.
Enter the hidden menu, (A,B,C held in + power on)
While transmitting in AM adjust menu item 60 (AM Carrier Level) for no or a minimum reading on ALC meter. This will allow for positive modulation.
Experiment a little bit, My rig out of the box was set at 142. This allowed NO positive modulation.
My new setting is 113 which gives a nice waveform and minimizes carrier shift.
The ALC cicuitry is a little frequency sensitive so you may need to do this every time you change bands.
Of course document the original value plus your new setting. After returning to regular TX mode you may notice that the ALC level has increased somewhat but you still get a nice waveform on the scope."


I'm going to bed now. I tried to get tonight of but SOL.

 

[Shockwave]

This line of Yeasu radios has hideous AM when compared to a typical CB. The low level IF modulation is quite poor when modulated hard. The ALC setting will help reduce the downward swing but loud audio is still missing. Perhaps I'm too critical but I think this rig loses it's ability to sound clean at a much lower percentage of modulation then I like. If you're willing to do some work, you can make this radio sound as good as anything else on AM. It requires modulating the DC voltage feeding the pair of RF driver transistors.

My first tests were simply connecting the modulated DC voltage from a Cobra 148 GTL to feed the drivers of an FT-857. This drops the unmodulated voltage to the drivers from 12 to 6 but modulates the 6 volts back up to 12 on positive peaks. It requires a little higher carrier setting to get the 25 watts but the positive peaks go well over 100 with no distortion driven hard with audio. Not too difficult to mount the series pass modulation transistor on the Yeasu heatsink and drive it from the mic preamp. Feed the RF drivers with 12 volts DC for all modes other then AM.

 

[Captain Kilowatt]

All I can say is that there was a huge difference in the quality and volume of the receive end after making the changes. From a 25 watt carrier I can hit peaks of 90-100 watts and still sound clean. It looks good on a scope too. I use no compression and only have moderate TX EQ settings. FWIW it is a relatively new unit, purchased just this past spring.

 

[Shockwave]

I wonder if there have been any changes to the AM modulator from the early versions to the newer D models. The newer ones include some of the options for free like the DSP and maybe the high stability oscillator. I know the new versions have corrected a serious instability issue in the 6 meter transmitter. The original FT-857 and FT-897 could oscillate on 6 meter TX so bad many were unusable on the band. Thousands of the old ones have this problem and yet the FCC passed the certification and Yeasu won't admit they screwed up or even post a service bulletin. You bet they fixed it though on the FT-857D. They all have different, lower gain FET drivers with slight circuit changes to make them stable on 6.

Captain, as I recall before I modulated the RF stage in mine for AM, if my positive peaks hit anything over 100%, the positive peaks would appear to "invert" for lack of better explanation on the scope. This is common with many rigs that modulate AM through the SSB balanced modulator. It leaves no head room if you modulate the rig heavily and hit anything over 100%. Usually causing objectionable distortion very abruptly at this point. Forcing the user to keep the audio on the light side for best clarity. Since you have the newer model I am curious if you can run the carrier down to reach 125% positive peaks without seeing the effect I describe?

 

[Captain Kilowatt]

Hmmmmm I don't know.I'm not a modulation monster anyway and 100% is fine for what I want. Everything is in a bit of a mess right now with a new shack rebuild but after I get things hooked back up perhaps I can run a test and have a look. Ironically I was just measuring the new desk up for a shelf I plan to make this afternoon. The shelf is to be used to hold some test gear including the scope and Wavetek mod meter on top of the gear.

 

[Quiksilver]

Do these changes only affect AM operation? Meaning; do I need to re-adjust radio for SSB operation?

Thanks!!

 

[TonyV225]

How are you guys setting up the FT-857 and FT-957 radios on AM? For some reason when my family went on vacation to Georgia this past July I woulld flip to AM to 27.185.00 for traffic reports but the receive was horrible all garbled like the frontend was being overloaded so AM couldnt be understood or used for that matter.

 

[Captain Kilowatt]

There is nothing to change for receiving AM mode on the 857/897 rigs. I have never had a problem with what you describe on AM with my 857. For transmitting AM I simply made the AM ALC adjustments in the service menue as detailed earlier in the thread. I'm wondering if you had the notch filter on and centered which would null out the carrier making things a bit garbled.Also if the signals were really strong you need the noise blanker turned off or way down to avoid distortion.

 

[TonyV225]

Im wondering if the noise blanker issue you described is my problem?? Ill have to bring the radio in and give it a look. Thanks....

 

[Carl E Holcomb]

This line of Yeasu radios has hideous AM when compared to a typical CB. The low level IF modulation is quite poor when modulated hard. The ALC setting will help reduce the downward swing but loud audio is still missing. Perhaps I'm too critical but I think this rig loses it's ability to sound clean at a much lower percentage of modulation then I like. If you're willing to do some work, you can make this radio sound as good as anything else on AM. It requires modulating the DC voltage feeding the pair of RF driver transistors.

My first tests were simply connecting the modulated DC voltage from a Cobra 148 GTL to feed the drivers of an FT-857. This drops the unmodulated voltage to the drivers from 12 to 6 but modulates the 6 volts back up to 12 on positive peaks. It requires a little higher carrier setting to get the 25 watts but the positive peaks go well over 100 with no distortion driven hard with audio. Not too difficult to mount the series pass modulation transistor on the Yeasu heatsink and drive it from the mic preamp. Feed the RF drivers with 12 volts DC for all modes other then AM.

 

[Carl E Holcomb]

will you send me an email showing how you the 148 gtl parts in the ft897. my email is n5tfu@yahoo.com