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Author Topic: Clean RF RF demodulator.  (Read 33337 times)
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ke7trp
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« Reply #25 on: June 20, 2010, 11:32:33 PM »

Wow steve.  Thats cool. I wish I could afford a scope like that.  I have an old Tech we paid $20 for.  PRetty neat..  I bet those big dollar scopes will come down in price and I can get one this year.


C
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Steve - WB3HUZ
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« Reply #26 on: June 21, 2010, 08:30:34 AM »

Guess you didn't read my post.    Cheesy   I typed:

Quote
Several ham fest $20-40 scopes have served as my mod monitor for the last 20 years.

I also have a 100 MHz Tek that I got for $75. Take a look at the next hamfest. You may snag one.
  


Wow steve.  Thats cool. I wish I could afford a scope like that.  I have an old Tech we paid $20 for.  PRetty neat..  I bet those big dollar scopes will come down in price and I can get one this year.


C
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WA1GFZ
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« Reply #27 on: June 21, 2010, 09:54:35 AM »

a 1 GHz scope is great for looking at a class e rig waveforms
My point is a good scope is cheap so why spend a bundle on an interface that does the same thing as a real scope trigger circuit. TEK LCD scopes are great but you have to learn how to use it.
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w3jn
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« Reply #28 on: June 21, 2010, 10:22:29 AM »

I've got several 100 MHz scopes and never paid more than a hundred bux for any of 'em.  My 7903 has the freq counter plug in and it triggers perfectly.   I also have a Gould portable scope (the size of a 2245 etc) that's got a built in freq counter and it works FB on AM signals.  A decent hamfest will cough one up almost every time.
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WQ9E
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« Reply #29 on: June 21, 2010, 03:57:01 PM »

The other issue with tunnel diodes is they are known for changing characteristics and a number of folks have written about searching for replacements for their vintage Tektronix scopes.  I have some old 500 series lab scopes and plug-ins that use tunnel diodes but so far they have been good to me.

Didn't Heathkit make a dip meter using a tunnel diode?
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Rodger WQ9E
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« Reply #30 on: June 21, 2010, 07:28:11 PM »

And it dont got no stinkin BNC conecters.........................


klc


* RM 45A.jpg (125.48 KB, 500x375 - viewed 491 times.)
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WQ9E
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« Reply #31 on: June 21, 2010, 07:48:45 PM »

Real boat anchor scopes have a separate power supply and the requisite scopemobile Smiley 

The type 555 dual beam with plug in time bases and vertical amps.  Both the scope and power supply have cooling fans and it will never get an energy star award.


* scope front.JPG (196.02 KB, 465x1024 - viewed 499 times.)

* scope left side.JPG (321.63 KB, 1024x683 - viewed 475 times.)

* scope right side.JPG (319.42 KB, 1024x704 - viewed 483 times.)
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Rodger WQ9E
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« Reply #32 on: June 22, 2010, 08:36:29 AM »

And it dont got no stinkin BNC conecters.........................


klc

http://amfone.net/Amforum/index.php?action=dlattach;topic=24445.0;attach=20152


I used to have one of those. It was one hell of a scope, HOWEVER....................

It took 4 men, 2 boys, 3 teams of horses and a tribe of indians to move it!! It would also do a nice job of keeping the shack warm in the winter!! The fellow I gave it to is still using it!
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K5UJ
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« Reply #33 on: June 22, 2010, 12:35:00 PM »

those are some beaut tube scopes--do you have to run them on 115 v. for the tube filaments?

I just scored a Tek R7704 for the bench and a small Sola 500 VA 120 v. conditioner.  I have no idea what I'm gg to do with it but the price was too good to pass, so I figured I'd experiment with power conditioning and see what it buys me.
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ke7trp
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« Reply #34 on: June 22, 2010, 12:59:58 PM »

While all scopes provide triggering selection control, it does no good to set the trigger up to source "internal" off the input you are feeding from a stand alone sampler.  In order to hold the wave form in a synchronized way, one MUST use a base-band RF reference rectified EXTERNAL trigger signal.  The Clean RF has provided this option, in addition to providing a separate audio source feed to their 1/4 TRS headphone jack with volume control.
 
When I move the trigger selection to internal off from their external based signal, the wave from DOES NOT stand still, it moves all over the place every time I change the pitch of my voice, the CleanRF Systems external trigger solves all that.  I can not believe I used a stand alone sampler for some time.  It is junk, you need to trigger the signal.  If you have any questions, go to their site, the documentation is off the chart. 

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ke7trp
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« Reply #35 on: June 22, 2010, 01:15:54 PM »

Your not understanding.  I tried over and over to explain to you.  Maybe you have to see this work in person before you get it.

C
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WD5JKO
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« Reply #36 on: June 22, 2010, 05:15:58 PM »

Jim,
Does your 2225 have a high frequency reject position for trigger coupling?  

Roger,

   Yes it does, and some other options. The trouble with triggering this way is that the results are inconsistent with most any setting using my voice as a trigger source. As a result I use X:Y mode mostly since with a Trapezoid pattern there is nothing critical about the setup.  

  Boy listening to some of the other posters here, we got some pretty high level scope users here on AM Fone. I bet some of these guys could analyze perfectly a single shot 20ns pulse with a Hickock OS8 oscilloscope.  Grin

http://www.oszimuseum.de/oszimuseum/equipment/manufacturer/hickok/os8bu_200.jpg

Jim
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Steve - WB3HUZ
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« Reply #37 on: June 22, 2010, 06:08:34 PM »

http://www.tek.com/cgi-bin/rfbypass.cgi?link=http://www2.tek.com/cmswpt/tidownload.lotr?ct=TI&cs=pri&ci=2280&lc=EN
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WA1GFZ
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« Reply #38 on: June 22, 2010, 08:00:40 PM »

7704 is a nice scope a slower 7904.
I've seen the manual on line free. BTW I just downloaded the service manual for my 2240 for free.
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KX5JT
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« Reply #39 on: June 22, 2010, 08:17:33 PM »

Wow.  I feel like I need to take a class on the oscilloscope now.
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ke7trp
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« Reply #40 on: June 22, 2010, 08:38:11 PM »

Boy, these guys still are missing the point.  It is not whether the scope has a trigger, it is whether it provides the base-band signal to trigger the RF band input.  What is so hard to understand about that???   

Not trying to argue here.. I just think you are not understanding why its important to have the base band signal Trigger.

C

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WQ9E
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« Reply #41 on: June 22, 2010, 09:03:46 PM »

Like many of the others here I have several Tektronix scopes and the trigger circuit WILL trigger on either the RF "carrier" or the modulation component depending upon trigger setting and sweep speed.  That is a basic requirement for a good scope, that it can trigger on different components of a complex waveform.

If you are using a Heathkit SB-610 or similar recurrent sweep scope you are going to struggle to get a stable pattern.  But if any of my Tektronix scopes were unable to provide a stable display of a modulated carrier or a string of CW dots or dashes it would be time to troubleshoot the timebase and its triggering circuit.

Tektronix scopes were standard equipment in most AM, FM, and TV stations from the 50's onward.  The only thing used beyond the standard trigger circuit was a unit allowing switch selectable display of any line of an NTSC waveform; even this could be done using a dual timebase unit in "A delayed by B" mode but it was a lot easier to switch select with the dedicated trigger unit.  Tek later build specialized display monitors for TV use with this trigger/timebase built in.

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Rodger WQ9E
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« Reply #42 on: June 22, 2010, 09:35:34 PM »

Roger,

  I just got off 75m where I ran AM, SSB, and AM again. The first two were with my 20A. I use the 20A audio sample output to the second channel and the modulated RF in the other. The scope is a Tek 2225 (50 mhz). Everything worked perfect, as the triggering was stable, and repeatable.

  Then I switched to my Gonset G76 where I could only use one scope channel since I have no external audio here, so I had to trigger on that. The results were not very good. After the QSO I switched to a dummy load to examine the issue further. Playing with the trigger level, trigger coupling, LF reject, sometimes HF reject, and a few other knobs I could trigger the scope repeatedly with exact sustained Yeaaaaaaa Yeaaaaaa. Then say Hellllllooooo, Hellllloooo and I need to fiddle with the knobs again. For each sustained syllable, varying the sweep rate fine knob reveals sweep rates that will not trigger on, and others that will, and do so repeatedly.

   So my belief that a mid level scope like a 2225 is not so sophisticated in the trigger department, and possibly suffers some from age (leaky or diminished capacity electrolytic condensers). The operator (me) might suffer from some of the same ills.  Grin

   If the product Clark posted would enhance the capability of a modulation monitor scope like mine, then why would folks infer that the problem is simply a short between the headphones?

Jim
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ke7trp
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« Reply #43 on: June 22, 2010, 09:42:17 PM »

I am not sure..  I honestly think it is because they have not used the Trigger setup like this.  I have an old Tek scope. Ancient model 422.  It works 100% with the outboard Trigger from the Clean RF device. I used scopes for years without the Trigger and I had no idea what I was missing. Now that I have it, I wont go back.



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Steve - WB3HUZ
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« Reply #44 on: June 22, 2010, 09:56:09 PM »

Rodger is on point.  If you have a scope with a good trigger section (and you know how to use it), the baseband trigger input is not needed. This is not an arguable point. It's been done for years. It's not a misunderstanding of what anyone is saying or what the CleanRF box does. It's the FACT that the CleanRF box is not needed given the right circumstances.

I have a 2235 and I have no problem triggering on AM waveforms. It's a few years older than the 2225 but nearly identical, except the BW is 100 MHz vice 50 MHz. Just like my cheapie BK Precision 1541B (which also triggers on the AM envelope FB), the trigger section has LF coupling. I find with the proper setting of the timebase and if needed, the hold-off control, the LF coupling isn't even needed. But using it, does make things easier.

 I don't think anyone implied there was a "short between the headphones." If you inferred that, then it's on you. We can all learn from the experience of others. I don't see someone teaching me something as implying I'm stupid (even if I am stupid, as is often the case).  Cheesy

That's it and that's all. No arguing and no one-ups-manship.



* hihi.jpg (35.1 KB, 352x400 - viewed 505 times.)
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WQ9E
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« Reply #45 on: June 22, 2010, 10:05:47 PM »

Jim,

It is very possible that your trigger circuit is not operating as intended.  The full calibration procedure for a scope is not even close to rocket science but it can be tedious and like everything else test gear requires periodic checks and calibration.  Calibrating test gear is actually the most important calibration since everything else you repair is dependent upon your test gear performance.  I can calibrate most analog Tektronix scopes in an hour to 90 minutes max.  Some of the early scopes, like the Type 555 pictured earlier, take longer since the vertical delay line is composed of L/C circuits instead of a simple coaxial line.  Adjusting these requires a fast rise square wave generator and a bit of patience to adjust the delay line to provide the required delay without changing the waveform.  Scope makers soon discovered a coaxial line could be used to provide the delay and that takes a couple of hours out of the typical calibration.  The delay is necessary to allow the time base to be triggered to start the horizontal sweep before the vertical signal is applied.  Otherwise you would not be able to see the actual triggering event.

To trigger on the audio component you want to set if for HF reject.  I have never used the model you own but it really should cleanly lock with little/no fiddling of controls and once the trigger settings are adjusted you should be able to switch sweep time per division without resetting this control (until you move outside the speed range where the trigger mode you selected doesn't make sense; i.e. setting a very fast time per division when what you actually want is the audio component).

Clark,

I have no issue with the box you are using.  If you have a scope that either has a less sophisticated trigger/time base or one that isn't working properly then it essentially provides a hard trigger for the time base based upon the audio component.  But for the scopes that are commonplace in many ham stations it isn't necessary.  

In general, if you are repairing your own gear owning and learning to use a good scope will pay you back many times over.  I have used the scopes several times to locate those annoying intermittent problems that plague both modern and vintage gear.  Some things can only be done properly with a scope and many measurements are much easier with a scope.  I like the Tektronix 7000 series because they are inexpensive (at hamfests) and very versatile with the available plug-ins.  I have several of the 7000 family but most used are my 7854 models which provide a conservative 400 Mhz. bandwidth with storage and waveform analysis built in.
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Rodger WQ9E
ke7trp
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« Reply #46 on: June 22, 2010, 10:13:53 PM »

Thanks Steve.  I will look for a better scope at the next swap and swindle. 

C
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K5UJ
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« Reply #47 on: June 23, 2010, 12:46:54 AM »

7704 is a nice scope a slower 7904.
I've seen the manual on line free. BTW I just downloaded the service manual for my 2240 for free.

Thanks Frank; I'll look for the manual.  The 7704 will probably handle anything I get into. 
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WA1GFZ
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« Reply #48 on: June 23, 2010, 08:46:53 AM »

Da, my digital scope is a 2430. I think the memory hold up battery is shot.
It started coming up with faults a month ago. After some reading it appears the calibration constants are messed up. I need to replace the battery which will force a relaod of a default base line table so it will calibrate itself again.
My 7623 just keeps working. The old 7000 scopes were great. 4XX series had problems with transistor sockets. Best way to fix the problem is to solder the transistors into the socket. 5XX worked great and make nice room heaters.
My old 545 drew about 7 amps off the line. The new LCD scopes are cool once you learn how to use them.
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ke7trp
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« Reply #49 on: June 23, 2010, 01:11:16 PM »

7704 is a nice scope a slower 7904.
I've seen the manual on line free. BTW I just downloaded the service manual for my 2240 for free.

Thanks Frank; I'll look for the manual.  The 7704 will probably handle anything I get into. 

Rob. How is the design stage comming along?

C
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