I think I just learned a lesson....

[guitar_199]

A few days ago ... I used the waterfall display on my Icom 7300 to look at the output of that relatively recent Uniden PC68XL of mine (no DIRECT CONNECTION! The 7300 had no antenna connected, and I was transmitting into the halfwave antenna outside... the 7300 just picked it up!). That is the day that I discovered that the PC68 was about 330 Hz or so high. I know the 7300 isn't a piece of lab equipment...but it is probably close enough for this test.

I went back and looked at something else.........and was horrified.

A few days further back I posted some observations saying that it LOOKED LIKE that modulation control was good on the PC68....because of the apparent action that I saw on my modulation meter. It actually LOOKED like the modulation was being squeezed in at the top...just by watching the needle.

WRONG-O!!!!!!!

When I "whistle modulate" into the microphone.... I can see the carrier in the middle........but when I modulate... I see AUDIO HARMONIC SPIKES from the carrier out on BOTH SIDES. Should just see one spike on each side. But I mean.....I could see probably 8 or 9 spikes ON EACH SIDE of the carrier.... all pretty equally strong.

I opened the case up.... found the AMC level control...and I can NOT see where anything is disconnected/disabled at all. As far as I can see....everything is there......BUT it looks like the level control may have been spun around to max.

I am having to work from home so I can't dink with it any further now.... but this weekend that baby is going on the bench for a look with the spectrum analyzer to see if I can confirm this. May drag in the freq counter and run an alignment while I am at it.

But still...I think it is obvious that just "looking at the modulation needle" doesn't give me the "accurate picture" that I thought it did!!!!!

 

[freecell]

if you're seeing that beyond 5 khz. either side of center frequency then you might have a problem. in am operation the upper and lower sidebands should not exceed 5 khz..

 

[guitar_199]

Exactly! And, since I was whistling.... NOT driving a tone from a generator... I can't tell you exactly what the frequency was.....but I can tell you the harmonics are EASILY into the next channel... probably WAY into the next channel.

And ... while the mileage of others may vary..... I do not like splatter boxes.I pulled it off of the cable as soon as I saw this. Just one of my wierdnesses!!!!

if you're seeing that beyond 5 khz. either side of center frequency then you might have a problem. in am operation the upper and lower sidebands should not exceed 5 khz..

 

[Handy Andy]

But still...I think it is obvious that just "looking at the modulation needle" doesn't give me the "accurate picture" that I thought it did!!!!!

No, but the "waterfall" effect you saw, can go a LOOONG way in trimming up the messy output of the '68 - I'd try that more than a secondary tester - see if that would provide the better tool for trimming while you watch the waterfalls' narrowing / widening change as you work the limiter AMC control.

Now a Whistle? Not exactly the best input source for mic's - being full of noise and can make the operator light-headed and possibly encounter a fainting spell from the excessive need to be "ventilated" during the test procedure.

You'd miss the show...

 

[tramd]

No, but the "waterfall" effect you saw, can go a LOOONG way in trimming up the messy output of the '68 - I'd try that more than a secondary tester - see if that would provide the better tool for trimming while you watch the waterfalls' narrowing / widening change as you work the limiter AMC control.

Now a Whistle? Not exactly the best input source for mic's - being full of noise and can make the operator light-headed and possibly encounter a fainting spell from the excessive need to be "ventilated" during the test procedure.

You'd miss the show...

Now that would make for a pretty funny meme. A guy passed out laying on the floor with a mike in his hand and his wife standing over him with her hands on her hips shaking her head, thinking what a moron he his.