The AM Forum

i have heard about the shark fin look on the scope and was wondering if this was kinda closee to it. the top is just a tad flat but i do see a fin off to the side of it.

 ;D
http://www.youtube.com/bspn33#p/a/u/1/vJYB5wVNVdc

this was recorded off the if output of a r390

I just love that audio ;D ;D How can i get some ??? ??? ???

Back swinging the monkey!

ohhhhhhhhhh nooooooo Mr Bill!!!!

Looks like it's out of phase and no high frequencies.
If you are using a professional microphone, you can reverse the leads. If you're not running balanced audio to the TX, You can reverse the plate leads on the modulator tubes AFTER THE TX IS OFF AND HV DISCHARGED.....
Sorry for loud voice.

Any EQ used? Usually the settings resemble a smiling face, somewhat.

This link is a better representation of a well modulated TX

http://www.youtube.com/watch?v=pvowzE_XYl0

You modulation looks like out of phase.
Listening sounds like a transistor audio amp and the bias set wrong. audio choppy and extreme distortion.
Modulator tubes bias set up properly??
You're moving along and making AM
Fred

The guy on there is among those who taught The Derb how to Swang a Munkey. just FYI.

i remember a vid that derb did on youtube i wish was still on there. i forgot what amp it was but he was tuning it with the watt meter and having some fun with it. 

Looks like the good buddy was using a class C "linear" amp.

While we are on the subject, here is my scope pattern on the newly acquired Viking II.
Do I need to add a negative peak limiter?

http://s271.photobucket.com/albums/jj131/kx5jt/?action=view&current=scope.mp4 (http://s271.photobucket.com/albums/jj131/kx5jt/?action=view&current=scope.mp4)

That or turn down the mic gain. Also check your audio polarity.

Agreed.

Where the pattern expands above and below the base line are the Positive peaks.  the Negative peak is where the plate voltage is reduced to 0 in the final.  You've got too much audio.

As Steve suggested, check the audio polarity, as well.  Might be the plate caps on the 807's. 

To see how much positive audio you do have in that rig, I'd suggest adjusting the carrier to the point where it consumes 2 divisions on the graticule, then talk to it.  100% will be when the positive peaks reach 2x as high as the carrier, at the same time as the carrier is pinched at the baseline (and not that long line between peaks which represents OVER-modulation).  Make note of where your pattern peaks are.  This establishes a reference point. Make your changes, and check it again.  With the carrier consuming 2 divisions, at 100%, your peaks should reach close to 4 divisions, up/down from the base-line.

Also, I see some hummmmmm on the carrier.  That's probably being picked up by the scope being near an AC field of a transformer. If the Scope is on top of the transmitter - not a good idea.  Or, it's the single lead inside your tuner-box that's getting hum induced into it.  This is why I suggested sampling RF out in the field of the antenna.  Probably best to use some RG-58, run it outside, and make a loop in the coax of a few feet, and lay it on the ground, or hang it in a tree, or something.

Here's what I was able to capture, so you know what I'm talking about..

That solid line between the patterns, is over-modulation.  that's the base-line and shouldn't be cut off like that.

Your carrier consumes 4 divisions on the graticule of the scope.  Your peaks should not be rounded off at the tops (means you're flat-topping - not enough audio voltage and/or reversed audio lead/plate-leads on the modulator), and should consume ~8 divisions, without pinching off the carrier (like the picture shows).

Hang in there, John!  We'll get ya straightened out, yet! :-)

Thanks Geoff.  I knew I was overmodulating.  As you see I do put the carrier for the center half of the scope (2 divisions above and below the centerline).  I am hitting the top and bottom pretty easily. 

The problem is when I drop the audio on the front panel to the point where the there is no white lining (or flatlining like I like to call it), then the positive peaks barely make it to the 70% level.   It just don't look pretty. 

I'll try swapping the plate leads on the 807's tommorow night when I'm back in the shack.  Although they look like they belong to each tube they are on, I have read that vocal symmetry can vary from person to person.  Can't hurt to try it.

Well... I set mine to 2 divisions (one above, one below).  SOMEwhere around here, I have a video of it and need to capture a screen-shot and show you why I need only 2 divisions for the carrier... it's because the audio is pretty much going off the top and below the bottom of the screen  ;D
[quote
The problem is when I drop the audio on the front panel to the point where the there is no white lining (or flatlining like I like to call it), then the positive peaks barely make it to the 70% level.   It just don't look pretty. 
[/quote]
It's FAR better to be UNder-modulated than OVER-modulate like that, when it comes to keeping peace with those that share our spectrum, and not necessarily our views.

In other words, if you don't want the wrath of some SillySideBander coming up and saying "hey, man!  Yer splattering all over the band!" because, well... he'd be right and then there starts the war.  If we don't give 'em a reason to bitch in the -FIRST- damn place, we can help keep the bad feelings down to a minimum.

Besides, it's the right thing to do (not over-modulate, that is).

As far as getting the positive peaks up there, yeah.. check the polarity of the microphone, and the plate-caps on the 807's.  When Jerry put the Valiant mod transformer in there, they might have gotten reversed.  (not knocking Jerry's technical ability - I've done the same thing)
[/quote]
I'll try swapping the plate leads on the 807's tommorow night when I'm back in the shack.  Although they look like they belong to each tube they are on, I have read that vocal symmetry can vary from person to person.  Can't hurt to try it.
[/quote]

It does vary from person to person.  Female voices are -most- difficult to manage!  You could always monitor the output of your microphone with your voice on your scope.  That'll give you an idea of what YOUR voice patterns are like.

A trick I use to get more detailed resolution with my scope is to set the base line right at the bottom of the screen, not midway up towards the top.  The envelope pattern by definition is symmetrical, so the top half is inevitably a mirror image of the bottom half.  Move the sweep line down to the bottom of the screen and double the vertical gain (or halve the attenuation) so that the pattern once again fills the screen, and you will get a closer-up view of the envelope pattern. You may want to also double the sweep frequency to keep the shape of the pattern the same.

I'll check that out Don...........Looking at both sides enables me to determine if the modulation is out of phase. Just looking at only half might not reveal phase............i'll do some lookin'
Fred

As funny as it is to hear these clowns tear up 27 MHz, what's funnier is the worse they sound the more they tell each other they sound good... as long as they're loud. 

I think those are Guppy Fins you're seeing.

Mark

I can tell I'm out of phase when I hit the baseline before I modulate 100 percent positive.

I think I might build a project box with a dpdt toggle switch labeled Phase Reversal and put it in line.

I like that technique Don.  I just tried it.

Beats getting inside the TX and switching plate caps!

No, that would be much easier BUT I also have other rigs, including a DX-60 that could benefit from using a project box, there are no push pull modulator tubes in that rig or in my ts-570 Steve. ;)

Yep. Put the box in line at the point where your outboard audio gear feeds the transmitters. Should be FB.

I hear the same thing all the time on the ham bands when I tune in slopbucketeers.  I hear some of the nastiest, raspiest crappiest sounding audio imaginable, and the other guys in the QSO tell him he "sounds good".

Sadly I hear it too on A.M.  --- Give me an HONEST report, because that's what you're getting from me!

You're five-nine. I say again, five-nine!  Now please repeat your call sign several times. I can barely hear you through all the noise, and the QRM is covering up your signal... You're five-nine.

Thanks Old Man you're 59 too, gud luck in the contest!

Almost no one give out correct reports compared to the definitions below.

An S9 would hardly ever be given. Many R3 and R4 reports would also be given, even though the guy on the receiving end is getting 100% copy.

R = READABILITY
1 -- Unreadable
2 -- Barely readable, occasional words distinguishable
3 -- Readable with considerable difficulty
4 -- Readable with practically no difficulty
5 -- Perfectly readable

S = SIGNAL STRENGTH
1 -- Faint signals, barely perceptible
2 -- Very weak signals
3 -- Weak signals
4 -- Fair signals
5 -- Fairly good signals
6 -- Good signals
7 -- Moderately strong signals
8 -- Strong signals
9 -- Extremely strong signals

T = TONE
1 -- Sixty cycle a.c. or less, very rough and broad
2 -- Very rough a.c. , very harsh and broad
3 -- Rough a.c. tone, rectified but not filtered
4 -- Rough note, some trace of filtering
5 -- Filtered rectified a.c. but strongly ripple-modulated
6 -- Filtered tone, definite trace of ripple modulation
7 -- Near pure tone, trace of ripple modulation
8 -- Near perfect tone, slight trace of modulation
9 -- Perfect tone, no trace of ripple or modulation of any kind

Notice there is a BIG gap between a readability 3 or 4.

3 -- Readable with considerable difficulty
4 -- Readable with practically no difficulty


When an S-meter is properly calibrated and the RST "ear" guidelines are followed for reports, most hams are disappointed when they hear their reports.  Getting a 4X5 is really a good report, but many guys would start looking outside to see if their antenna was still up... ;D

When receiving a report, it is important to also listen to the reports given to other stations, so we can see how we compare with the average station.  If we're running QRO and the station is giving everyone a 5X5 and you get a 5X8, that's a good thang. If he's giving everyone a S9+20 and you get a 5X8, that's a bad thang...

Relativity is what it's all about with reports.

Another thang: The most important thing hams want to know is, "How loud is my signal compared to others?"  We should always watch the meter carefully and as a service give out exact meter readings. The biggest waste of time is to hear someone say we are 59+++ or just 59.  If hams weren't interested in reports, they'd be on Skype. Most hams are naturally a competitive lot.

T

When i was moobilin a lot, I'd work SSB. I  made the mistake of giving someone a report in a corntest... Your S4 to S5....  "Well which one is it!?"  I guess I was insulting him.

 I'll start giving out S10's.  That oughta make 'em happy.

klc

Too often these days, I hear signal reports of "you're S-9 to S-10"...

huh?

Signal reports are largely useless, no matter how "accurate." What does S9 mean if the noise level is S8? A good report would always include the signal referenced to the noise. And as Tom noted, some comparison to other signals from a similar location provides context.

Steve, I'm gonna be back in San Antonio the 12th of March for the weekend.  I'm looking to fire the rig up and do some operating.  Hopefully we won't be in full-force Spring-time thunderstorm season.

When and Where do you typically operate so I have a better chance of finding you on the air, rather than shot-gunning the whole damn band trying to find a decent AM QSO?

3870-3885 kHz
3700-3725 kHz

Can someone clue me into how to tell if the modulation is out of phase by looking at the scope?

73

Rich

Look for the voice peaks with the greater amplitude above and below the edge of the pattern for the unmodulated carrier.  They should go in the positive direction, not in the negative.

Phase is not correct term, even though it is widely used. It is audio polarity.

Look at the three waveforms below. The first is with the audio polarity set for maximum positive peak modulation. The positive peaks extend well beyond 100 percent - entirely due to the asymmetry of my voice (no limiting used), as shown in the second waveform, which is the audio straight out of the microphone. Note the large amount of asymmetry.

Now look at the third waveform. This is the same audio as in the first two waveforms but with the polarity flipped. Notice that now with 100 percent modulation on the negative peaks, the positive peaks do not even reach 100 percent (about 80 percent). This is the undesired setting for the audio polarity.

Thanks guys, I see it!  (I think)

So this has only to do with the nature of our asymmetric voice?  We "connect" the part of the modulator that drives the RF up (positive peaks, away from baseline) with the part of our audio that is asymmetrically large.

Do I have that right?

Man, I bet my JVII is backwards, can't wait to check.   :)


Rich

You got it!

What if one tube is a bit stronger than the other?  Brandon gave me that tip.  Put it in the position that makes higher positive peaks.

Steve, BTW, thank you very much for those scope shots.

Rich

You're welcome.

Some more good info on this at the link.

http://www.arrl.org/files/file/Technology/tis/info/pdf/5405037.pdf

I tried to determine what the "phase"  (Would polarity be a better word?) was on the JVII.  Very difficult to find a definitive answer.  Just using my voice makes it hard because I can get various patterns depending on my volume and tone.  i did not see a definite difference in the positive peaks either way.........

Rich

Everyone has a different voice you might be more balanced than some of the nuts out there

Connect your mic directly to your scope. This will tell you if your voice is asymmetric or not.

Being balanced has never been my strong suit!

If your Viking cuts off the lows there may not be a whole lot of difference.
Low grid current can limit the positive peaks too.

I may have to re-think my advice then, of tuning a rig such as a viking II.  I've been suggesting that to tune the rig, put it in CW position (no key, or key down), and tune the oscillator/buffer circuit as shown by the book, and then adjust the grid drive to show 7.5mA of current.  Then, switch the meter to the plate position, quickly dip the final, and then make your loading adjustments (if needed) to bring it to ~180mA (saving 40mA from the suggested 220mA for a little 'breathing room' on the modulation transformer secondary, and slightly higher impedance in the final - 3.3k vs 2.7k) then reduce the grid drive, until you see the final plate current -just- start to drop.  bring it back, and leave it there.

I think think that would reduce the grid drive enough on a pair of 6146's to make any noticeable difference, but I could be mistaken.

I reversed polarity on my condensor by putting it into a different preamp with a "phase reversal" button.  The negative peaks are gone and the positives are higher.

I reversed the leads on the D-104 and got the same results.

Apparently my voice is backwards.  Thanks everybody for the help!

Just leave it at 7.5 mA from the start to finish.

The mod transformer rolls off below 250 CPS like a rock down a well.

I noticed on my Viking II when I pumped in sine waves, that 250 Hz started to distort before hitting 100%.  Up to 8Khz was fine... I didn't test higher, maybe I should.

the main thing with doing freq checks like that is look at how much more it takes to hit 100 percent mod.  most transformers will pass freqs the main thing is how much attenuation it has on the high freqs ya know. 

Except in the case where the modulation capability of the transmitter doesn't exceed 80%.  This could be due to deficiencies in a plate modulated transmitter, or a linear/grid modulated amplifier running at too high carrier efficiency.

Back in the 1930's there was some recognition of asymmetrical voice waveforms, and one school of thought was to set the carrier efficiency at something like 50%, and run the audio polarity so that the greater amplitude peaks extended in the negative direction.  It was argued that with the same tubes and power supply, more sideband power would be generated than when running at lower carrier efficiency but letting the greater amplitude peaks extend in the positive direction.

Good point.  I may have had to drive more audio into it, but I don't think it was much if I did.  I'm going to have to explore that I suppose.