Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
Splattermaster




 
The AM Forum
December 04, 2021, 03:11:58 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: 1 ... 4 [5] 6   Go Down
  Print  
Author Topic: Splattermaster  (Read 72293 times)
0 Members and 1 Guest are viewing this topic.
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 7918


CQ CQ CONTEST


WWW
« Reply #100 on: January 14, 2012, 02:10:40 PM »

3" CRT's were in the CE 100/200V, Cosmophones and maybe others.


CE 100V/200V's used a 2 inch scope (2AP1).
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
WA3VJB
Guest
« Reply #101 on: January 14, 2012, 02:18:42 PM »

A simple red/green light could show when something is being driven too hard. This would make more sense for the mass produced transceivers.

Like that RCA audio processor Gary/INR had:  "Normal," and "EXCESSIVE" with a row of LEDs to show how hard he was hittin' it.
Logged
Steve - K4HX
Guest
« Reply #102 on: January 14, 2012, 02:24:31 PM »

Exactly!
Logged
WD8BIL
Contributing
Member
*
Offline Offline

Posts: 4362


« Reply #103 on: January 14, 2012, 02:51:06 PM »

Quote
Which brings up a question..What is the best English word to say when looking at a modulation envelope in order to keep the display in sync? Mmmmm?

I just use a 1kHz tone generated in the Shure SE30 mixer, Bill.
Pickup an old audio/function generator and have at it!
Logged
ke7trp
Contributing
Member
*
Offline Offline

Posts: 3659



« Reply #104 on: January 14, 2012, 02:51:22 PM »

A trap pattern would be good I guess.  But a normal modulation scope is not going to show splatter. I guess at the very least, you could monitor your signal on a seperate receiver and roll the vfo around.  

In todays day an age, You can also just ask a guy with receiver and spec display to give you a Screen shot of your modulated rig.  


C
Logged
flintstone mop
Contributing
Member
*
Offline Offline

Posts: 5033


« Reply #105 on: January 14, 2012, 03:20:39 PM »

Real scopes have square screens Paul! I paid 20 bucks for this Tek 485 and got a clean Tek 453 from a neighbor for free. Life is good!
ROB, ouch!!!!
That display looks familiar. Like an over modulated Ranger TX. Squared off audio and those big spaces of cut-off carrier.

Nice bright display..........love these, once high dollar, cheap 'scopes.
Logged

Fred KC4MOP
k4kyv
Contributing Member
Don
Member

Offline Offline

Posts: 10062



« Reply #106 on: January 14, 2012, 08:18:31 PM »

CE 100V/200V's used a 2 inch scope (2AP1). 

Somewhere round here, I have a 1" scope tube.  IIRC, it has an RCA 900-somethig number.  Looks like a metal 6L6 with the top of the envelope made of of glass, which is actually the CRT screen.
Logged

Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
KM1H
Contributing
Member
*
Offline Offline

Posts: 3519



« Reply #107 on: January 14, 2012, 09:13:50 PM »

I have a couple of those 1" CRT's; one in a National scope and another in a HB one I picked up in a bunch of crap at an estate cleanout decades ago. Just found it again a few weeks ago.
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 7923



WWW
« Reply #108 on: January 14, 2012, 09:29:56 PM »

I have a NOS CRT for a Tektronix 500-series scope.

The part number could be useful. There are operating potential differences among the series and many different CRTs.
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 7923



WWW
« Reply #109 on: January 14, 2012, 09:37:11 PM »


The vertical and horizontal amplifiers in any good scope (ones you can buy for $50-100 at most fests) will be linear, especially at audio frequencies. The SB-614 and the Hohos are junk and should not be used for this or any other waveform monitoring.

Hohos?
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
W1AEX
Un-smug-a-licious
Contributing
Member
*
Offline Offline

Posts: 1483


Apache Labs SDR


WWW
« Reply #110 on: January 14, 2012, 09:45:58 PM »

Nice bright display..........love these, once high dollar, cheap 'scopes.

It cracks me up Fred that there are so many of them floating around out there for less than 50 bucks or even for free. I've seen several different original manufacturer list prices for the 485 but +$7000 seems to show up frequently. Maybe someone here knows what they actually sold for when new. It makes me think that with values like that we live in the best of times, eh?
Logged

One thing I'm certain of is that there is too much certainty in the world.
Pete, WA2CWA
Moderator
Member

Offline Offline

Posts: 7918


CQ CQ CONTEST


WWW
« Reply #111 on: January 14, 2012, 10:23:17 PM »


The vertical and horizontal amplifiers in any good scope (ones you can buy for $50-100 at most fests) will be linear, especially at audio frequencies. The SB-614 and the Hohos are junk and should not be used for this or any other waveform monitoring.

Hohos?

HO-10, HO-13, SB-610, SB-620 I guess, but you can probably add others to the list.
Logged

Pete, WA2CWA - "A Cluttered Desk is a Sign of Genius"
kb3ouk
Member

Offline Offline

Posts: 1624

The Voice of Fulton County


« Reply #112 on: January 14, 2012, 10:44:38 PM »

CE 100V/200V's used a 2 inch scope (2AP1).  

Somewhere round here, I have a 1" scope tube.  IIRC, it has an RCA 900-somethig number.  Looks like a metal 6L6 with the top of the envelope made of of glass, which is actually the CRT screen.

sounds like a 913. National CRM scope used one.
Logged

Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
KX5JT
Contributing
Member
*
Offline Offline

Posts: 1954


John-O-Phonic


« Reply #113 on: January 15, 2012, 11:56:01 PM »

I picked up a dual trace 40 Mhz Leader either on eBay or at a hamfest... not sure I actually got a few from both... it was under 40 bucks.  I use a BNC female to BNC female that attaches from my A trace to the back of the Johnson Matchbox with the RF probe.  Works great for envelop monitoring.  I can see when I turn up the audio gain that it will start flat lining with overmodulation so I cut it back until I have about  95% negative and 100% positive from the Johnson Viking II.   Today I asked Pete WA2CWA about my signal since he was working me on 15 meter AM with his Flex 5000.  He said it looked great with no artifacts or splatter, nothing seen outside of the normal bandwidth.  

I have never setup a trapezoid and I wonder if it would be as easy as pulling my audio out somehow to monitor it on the B trace?

Logged

AMI#1684
K5UJ
Contributing
Member
*
Offline Offline

Posts: 2845



WWW
« Reply #114 on: January 16, 2012, 09:52:36 AM »

I have never done this myself (caveat) but from what I have read here, the only way to get an accurate trapezoid with a plate mod. rig like the V2 is to get the audio off the modulator secondary using a voltage divider network (resistor string) and feed it directly to one pair of CRT plates on the scope.  how much voltage needed I don't know.
Logged

"Not taking crap or giving it is a pretty good lifestyle."--Frank
Steve - K4HX
Guest
« Reply #115 on: January 16, 2012, 11:08:43 AM »

That is false. The concept of running anything directly to the CRT plates is unsound and unnecessary if you have a good scope. It dates to the days when scope hams had access to had very limited bandwidth or were POS like the HOhos and other "monitor" scopes.


I have never done this myself (caveat) but from what I have read here, the only way to get an accurate trapezoid with a plate mod. rig like the V2 is to get the audio off the modulator secondary using a voltage divider network (resistor string) and feed it directly to one pair of CRT plates on the scope.  how much voltage needed I don't know.
Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2364


IN A TRIODE NO ONE CAN HEAR YOU SCREEN


WWW
« Reply #116 on: January 16, 2012, 11:28:22 AM »

That is false. The concept of running anything directly to the CRT plates is unsound and unnecessary if you have a good scope.

So we agree to disagree.

Diode demodulated samples will never make an accurate display in my opinion.

73DG
Logged

Just pacing the Farady cage...
Steve - K4HX
Guest
« Reply #117 on: January 16, 2012, 11:50:56 AM »

I was talking about scopes not diodes.

Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2364


IN A TRIODE NO ONE CAN HEAR YOU SCREEN


WWW
« Reply #118 on: January 16, 2012, 12:10:33 PM »

I was talking about the source of what the scope looks at.

Reconstituted audio from RF (from a diode or some other detector) is never as linear for display against the RF input for a accurate trapezoid measurement.

It manifests as 'bent sides', making one misinterpret the problem is a ratio error in the modulator/RF within the transmitter.

Like using a out-of-calibration VOM to build with.....

On most ham operations, it would be plenty OK, but to set up a big BC transmitter it just doesn't proof out.

Many here want to dot the I's, eTc, hence my references.

73DG
Logged

Just pacing the Farady cage...
KX5JT
Contributing
Member
*
Offline Offline

Posts: 1954


John-O-Phonic


« Reply #119 on: January 16, 2012, 12:11:29 PM »

I think I'll stick to just monitoring the envelop for now.
Logged

AMI#1684
Steve - K4HX
Guest
« Reply #120 on: January 16, 2012, 12:21:16 PM »

I understand and I completely agree. Any measurement is only as good as the sample/source. I still don't see how any of that relates to how the scope is used. Maybe I'm missing something (yea, yea, I know, a lot)?


I was talking about the source of what the scope looks at.

Reconstituted audio from RF (from a diode or some other detector) is never as linear for display against the RF input for a accurate trapezoid measurement.

It manifests as 'bent sides', making one misinterpret the problem is a ratio error in the modulator/RF within the transmitter.

Like using a out-of-calibration VOM to build with.....

On most ham operations, it would be plenty OK, but to set up a big BC transmitter it just doesn't proof out.

Many here want to dot the I's, eTc, hence my references.

73DG
Logged
W7TFO
WTF-OVER in 7 land Dennis
Contributing
Member
*
Offline Offline

Posts: 2364


IN A TRIODE NO ONE CAN HEAR YOU SCREEN


WWW
« Reply #121 on: January 16, 2012, 12:26:58 PM »

My comment isn't about the scope at all.  It is about how one hooks it up (or buys a 'one box' unit) to monitor modulation.

To wit, if you're running plate modulated tube rig, checking modulation via a trapezoidal pattern will not be accurate without a tap directly on the modulation transformer secondary.

I interpreted your earlier comment to assert contrary.

73DG
Logged

Just pacing the Farady cage...
k4kyv
Contributing Member
Don
Member

Offline Offline

Posts: 10062



« Reply #122 on: January 16, 2012, 12:44:19 PM »

If you are using a good quality lab grade scope, running the rf and af signals through the horizontal and vertical amplifiers should be OK. But why take up the desk space and tie up a useful test instrument as a permanent modulation monitor, when about any old el-cheapo HO-10 or other Hammy Hambone monitor scope will do the job? Bypassing the built-in amplifiers and feeding the plates directly guarantees linearity, especially if both deflection plates in each axis are excited in balanced fashion.  No noise/hum or spurious artefacts introduced, what you see is what your signal really looks like. Sure, it takes a larger signal sample for direct CRT deflection, but that means a better s/n ratio and less likelihood of extraneous pick-up and still should amount to no more than a fraction of a watt siphoned off from the transmitter output.

I can't think of anything that would be fundamentally "unsound" about feeding the plates directly.

My first monitor scope was homebrew.  I fed the vertical plates directly with the rf sample, and used 60~ a.c. for the horizontal sweep.  It kinda sucked, because I got two images superimposed on top of one another, moving across the screen in opposite directions, but I could at least tell my percentage of modulation, and with a little practice, it was possible to figure out what the envelope waveform looked like.  Then I came upon a  circuit, in a West Coast Radio Handbook IIRC, which involved adding fewer than a half dozen components (resistors and capacitors) that formed a 90 phase shift network, and feeding that shifted a.c. to the control grid of the CRT, so that it blanked out the trace over a half-cycle, virtually eliminating the undesirable re-trace.  Not perfect, because the display was expanded in the middle and compressed at the edges (since it was still half a sine wave and not a saw-tooth), and the sweep rate was fixed at 60~, but it still gave a pretty good indication of what the modulation waveform looked like.

I later replaced that scope with a hamfest find, some kind of speciality test instrument that had direct access to the plates and variable linear sweep, until the irreplaceable CRT crapped out, and by then I had acquired the HO-10, another hamfest bargain. I modified it to feed the vertical plates directly with rf and to feed the horizontal plates directly for trapezoid mode, disconnected the two-tone slopbucket garbage, and corrected Heathkit's shitty design that caused hum modulation on the display, and have been using it for years, with three other HO-10 carcasses in my junk pile for what should be a lifetime supply of spare parts.

One thing to beware with ANY CRT scope is that if you monitor in trapezoid mode all the time, it will eventually burn a vertical line in the middle of the screen, since whenever there is absence of modulation as between words or during speech pauses, the display is reduced to a bright vertical line.
I use trapezoid mode only for occasional checks for modulation linearity and a more precise indication of modulation percentage, and otherwise monitor the envelope waveform.

The envelope display will burn a horizontal line across the screen, and the trapezoid will burn a spot in the middle of the screen, unless some method is used to disable the display during stand-by periods.  I use a simple and dirty method that nevertheless works.  My T/R relay system operates with 28v DC, so I simply couple T/R control voltage to one of the horizontal plates, which shoves the baseline trace off-screen to one side, and during transmit, a set of relay contacts breaks the DC line and allows the baseline to shift back to its position on-screen.

It is especially important to use some method to blank the screen during receive/standby to avoid ruining a good test scope, if it doesn't already have an automatic trigger function to blank the screen in the absence of a signal.

To monitor one's CW waveform, it is best to simply turn down the brightness and leave the display triggered, since it would be difficult to interpret the display if it blanked out between dits and dahs.
Logged

Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

- - -
This message was typed using the DVORAK keyboard layout.
http://www.mwbrooks.com/dvorak
Steve - K4HX
Guest
« Reply #123 on: January 16, 2012, 05:41:49 PM »

I suppose there is nothing fundamentally unsound in bypassing the fuel pump in your car and pumping it by hand. But given the fuel pump works just fine, it would be rather silly to bypass it.

Good scopes for on-air monitoring can be bought at any hamfest for less than $100, often less than $50. Why mess with a POS like a HOho? You have to make kludges like connecting directly to the CRT plates, adding a triggering circuit, building a real power supply....  and you are still left with a very small screen. It's a waste of time and a far less effective way to make a measurement or monitor the signal. It's a hammy hambone way of doing things. I would never recommend to anyone to waste their time or money on a toy like a HO-10.

To each his own but the effort in getting a POS like a HOho to work correctly is better spent in other parts of the station.
Logged
Opcom
Patrick J. / KD5OEI
Contributing
Member
*
Offline Offline

Posts: 7923



WWW
« Reply #124 on: January 17, 2012, 03:37:20 AM »

Pulling the beam off screen is one thing, but running the beam current for minimum intensity during zero RF and audio and then causing it to increase to a normal level during modulation is more elegant and might have advantages depending what you want.

A scheme that will work for both the trapezoid and the amplitude monitor hookups is to rectify samples of both the audio and the RF and use them together to intensify the beam current. When no RF or audio is present, the beam is left dim (as set by the intensity control).

1.) Upon the first cycle of audio, a rectifier charges a capacitor and that voltage feeds to the control grid of the CRT through a resistor. The capacitor time constant is set for longer than the lowest modulation frequency so that upon modulation a DC steady voltage is produced.

2.) The same for RF, so that a DC voltage is produced according to the peak RF voltage.

3.) A special CRT trick is to add another RF detector and the time constant of the RF detector can be set to follow the audio waveform rather than filter it, just like an AM detector. A small part of this signal can be applied so that the effect is minimal at 100% negative modulation and maximized at 100% positive modulation. It has the effect of making the entire image of a much more uniform intensity, as opposed to leaving it to where the -100% part of the pattern has the same beam current as the +100% part of the pattern. It does not work 100% perfectly but it is a noticeable improvement avoiding bright spots/lines and large dim areas in the waveform or pattern.

Only a few volts or tens of volts is necessary to intensify the trace depending on the CRT. Each of 1, 2, and 3 can have its own screwdriver adjust pot to set the magnitude. The entire pot serves as the R of the RC time constant.

The wipers of the pots can each feed through a high value resistor to the control grid. The 'cold' ends of the pots should be connected to the CRT cathode. The value of these resistors depend on the values of the resistances in the CRT circuit and should be large compared to the resistance between the cathode and grid, about 10x, so that adjustments will not affect the brightness control much. The values of the adjustment pots should be about 1/10 the value of the series resistors so that the adjustments will have little interaction.

This assumes the CRT cathode is the connection for the decoupled negative HV CRT supply and the (more negative) grid bias comes from the brightness control wiper. If the CRT circuit is such that the decoupled negative HV CRT supply is connected to the grid and the cathode is therefore connected to the brightness control wiper, then the polarity of the voltages generated should be reversed (negative going) and the pot wiper series resistors should go to the cathode and the pots' common to the grid. The case could be either depending on the scope or the circuit chosen. Just throwing ideas on the table. A very lazy way of doing something similar could be to take the +HV for the CRT from the transmitter - when the HV is keyed on, the CRT accelerator is also keyed on. Depends on the CRT as most will be very dim with no 3rd anode voltage.


* CRT auto beam saver.png (7.14 KB, 628x284 - viewed 697 times.)
Logged

Radio Candelstein - Flagship Station of the NRK Radio Network.
Pages: 1 ... 4 [5] 6   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.087 seconds with 18 queries.