Clean RF RF demodulator.

[ke7trp]

After making my own Scope pickup and trying several different ways to hook up my Gates and Scope, I broke down and purchased The AM5K.

This thing is the best I have used for one simple reason. The Trigger now works on the scope. When I modulate my Transmitter, The pattern holds steady and does not dance all over the screen.  I dont know how I used scopes before without the Trigger. I am now selling off my Monitor scopes.  I wont use them again.

I got the AM5k and its working great with my GK500C around 300 watts of carrier. My scope has enough Gain to calibrate right on the money. Get the 2K if you have less power then the king does. I wanted to use one pickup for the King, The Big box and my T368 so I got the 5K model. I was worried it would not have enough output to the scope but I got lucky.

Also. The audio output jack and variable is a nice feature. I have been using it pumped through my audio system. Very clear and clean.

If you dont have time to build your own pickup, Just get this thing and be done with it. I am very pleased with it. It is VERY well made, Solid and has nice connectors and parts.  It also came with all the cables I needed.  First class for sure.

Now to get my USB O scope and 20 inch flat panel mounted so I will have a nice big scope on the wall in the shack!

I am not affiliated with him and dont know these guys. I just found it on the net and read up on the Triggering feature. Everyone seems happy so I purchased it.

c

[K5UJ]

I took an old $5 CB swr bridge, one of those things in a small steel clam box with a UHF jack on each end, meter, pot to adjust full scale forward, and slide switch for swr and turned it into something similar.  Some of them have a threaded recess on one end for screwing in a small field strength telescoping antenna.  Millions were made for Lafayette, Midland, Radio Shack, and a bunch of other CB manufacturers and you can get them for just a few bucks.  The inside has a rod between the jack centers and parallel rods for pickup.  Each are connected to diodes to rectify the RF and drive the meter.  One is for forward; the other reverse through the slide switch and the pot adjusts the current to drive the meter.  I drilled a hole and added a BNC jack and put the center of that on the meter pot wiper to get an adjustable level rectified signal to trigger on with the scope.  RF envelope tap is on the output of the 3-500s.  Diode tap is on exciter output.  Scope is an old Tek 453.  Very stable mod. envelope.  but I use the sb610 for trapezoid.   Of course this all works to the extent it does because I'm doing the exciter driving the leenyar thing.   When I run a transmitter I'll have to make some changes.

[ke7trp]

Yeah. I made my own out a an old Bud box and some connectors. This thing works so much better. I hate junk tossed togther. I like building stuff but if its not first class, I wont be happy.

I have it all integrated into the audio rack now. No RF anywhere its not supposed to be.  I was going to use this thing for every transmitter here. I might just get a couple more and Connect them on the back of each unit. This way, I can sample RF at the source of each rig in the room and leave the levels set. 

C

[KB9YSJ]

I Picked up 2 of them, one for the radio and one for my amp. Installed them and then I tuned up my amp with out looking at the scope. Then I looked at the scope and saw the pattern, It looked like crap. So with a few turns on Tune and Load, looking at the scope, My pattern was perfect. Ill never go with out these things hooked up again. Thanks Tyler I also got the 5K model.73

[ke7trp]

After a night of using mine, I am very happy. I used it with the T368 last night and was able to see that the pattern was horrible. I retuned it and set the audio up again and now have a much cleaner signal.  Those monitor scopes I used in the past are near worthless.  I love the Trigger feature. I dont have to try to hold a steady tone to adjust the rig.

C

[flintstone mop]

Thanks Carl, Ordered one for myself.
I got tired of the dancing displays too.

Fred

[KA2QFX]

Every bit as good or better than the Clean RF design and a LOT cheaper.

http://home.comcast.net/~msed01/RFpickup.html

If you don't mind building something.

[flintstone mop]

Every bit as good or better than the Clean RF design and a LOT cheaper.

http://home.comcast.net/~msed01/RFpickup.html

If you don't mind building something.

I think the magical part of the "CleanRF" is that it provides a trigger for the Oscope and you get a nice stable, non-dancing display.

fred

[WQ9E]

Most better quality scopes provide a choice of triggering the time base from low or high frequency signal content.  Trigger from the LF component to get a stable display of the modulation envelope. 

There may also be cases where you will need to use delayed triggering to examine part of a waveform.  In this case, one time base is used to hold off triggering for the other time base.  This same basic setup can be used to greatly "magnify" a portion of the waveform by using the first time base to hard trigger the second time base at the desired point on the waveform.

[K6JEK]

"A clean non-dancing display"  could you explain that a little more?  I just sample the RF out and feed that into an old TEK scope.  I can't say I love it.  Does this thing improve on that display

[ke7trp]

The design posted above is junk. I Tried it.  It does not work anywhere near as nice as the AM5k.  ITs lacking the entire trigger portion and its also for low power.

When you use the Trigger, You set the scope to EXT. So when your scope is triggered, the audio Frequencys dont dance around.  No matter if you put 500hz or 1000hz in, We see a nice display.  Maybe I can find time today to take some video with and without the Trigger so you can see it work.  Its clear some are not undestanding this.

I love mine!

C

[WQ9E]

For a clean display of the audio frequency component you have to trigger the scope time base on this component.  If your scope doesn't have the capability to trigger on the AF versus RF component then this gadget will provide that by generating a trigger source from its built in demodulator.  For most Tektronix, HP, and similar "lab grade" scopes the internal system will trigger "cleanly" from the trigger pickoff in the vertical amp. 

Of course if you have a line sampler you already like and a scope with a less sophisticated trigger system you can easily build a simple demodulator to provide an audio sample for triggering your scope.

[ke7trp]

I am running my station right now on 40.  Its cearly better using the AM5ks line to ext trigger. If I unplug it and try to use the internal on the scope, The Pattern is typical of what I was used too.  I have to hold a certain tone to get the picture to hold.  But with the demodulator set to ext the picture is spot on clear. Maybe my old tek is not happy trying to perform this funtion internal.

The Trapazoid is nice to have when tuning a Transmitter or SSB station. I found my Pro/Sb220 was out of tune this morning. Using the Trap feature, I was able to tune it linear. Then I switched back from Trap mode and set the audio right under 100. The guys actualy noticed on the air without me mentioning it. I bet my neighbors are much happier now.

I always used monitor scopes here on AM and SSB. But this is a new world for me. 

Neat toy.

C

[K5UJ]

Those things seem kind of expensive.  $129...over $200...for that you can do what I did and make a sampling rectified RF (audio) trigger source from an old swr bridge, buy a nice used Tek scope and/or SB610 monitor scope and have it all.   Actually, if I had to, I could get by with just the trapezoid.  If you have a dual trace scope, you can look at the mod. envelope with one trace and the rectified RF audio that you trigger on with the other trace.   It's just kind of fun to compare them.

[ke7trp]

Hey Rob. How about a challenge?  You up for it?  Build one that is better.. Then show it to us.

C

[K5UJ]

Hey Rob. How about a challenge?  You up for it?  Build one that is better.. Then show it to us.

C

Clark,

If your boxes work for you that's great.  I'm not trying to one-up you.   I just thought folks who can't afford those things might want to know about another way that is less expensive.   Maybe it's not as good--I don't know--it works well enough for me. 

[ke7trp]

Awesome.. Now just design something that works as good as this or better and post it Rob!

C

[ke7trp]

Cool.  Can you post plans for this and the parts list. That would be cool. 

C

[ke7trp]

I dont want to open mine. Its working so damn nice I will leave it alone. I just see all these comments on how you can build one and save money but then nobody ever shows how to do that.  Its like saying. I can paint my own house and save $1000.  But then when it comes time, They hire a crew and the job is done in one day.   I dont see any plans on how to make a device like this. The Trigger output is really working great. I took some videos of AM and SSB this morning. The Trapazoid is really cool on SSB. 

C

[KA2QFX]

The RF ammeter I posted is junk?  That method is used in thousands of lab grade devices for longer than I've been on the planet. I have built or used them from 5 watts to 25,000 watts.  Likely you didn't read my entire post. And I know what's inside the Clean RF box, there's no magic in a demodulated AC coupled output for trigger.  Sorry to have wasted your time.  Guess I'll throw away everything in my engineering library now that you've straightened me out. Thanks.

[ke7trp]

I am not sure what you are talking about on the RF ammeter thing.  Sorry.

Its easy to talk about how to make something like this. But its another thing to actualy sit down and make one with all these features.  Whats the shame in buying something if it works better then anything on the market?

I understand hams are cheap and they want to build stuff out of junk. I have made all kinds of things myself   But this thing has the base-band RF demodulator providing the EXTERNAL trigger and I have yet to see an easy way to do that nor do I have the time right now in life to try! 

I ran my unit at full power SSB today on 40. It was really neat seeing that envelope in sync. I was unplugging the trigger and going back to internal Time on the scope and wondering why I did not buy this thing 2 years ago when I first saw it! I guess I did not fully understand what I was missing.  I am sure someone will now come up with a parts layout that works like this one and offer an article and instructions. Maybe in QST!  They will probably Drill the rivets out and post pictures also.

Happy AMing!


C

[Steve - WB3HUZ]

I got something that works just as good and it costs nothing. It's called a good scope. I've never had any dancing patterns because I use a scope that has a decent trigger section. No external trigger is required. And it doesn't mean you need an expensive scope. Several ham fest $20-40 scopes have served as my mod monitor for the last 20 years.

I'm sure that box is nice. Have fun with it.

Awesome.. Now just design something that works as good as this or better and post it Rob!

C

[WA1GFZ]

Right on Mark, Heck I bought a TEK 7904 with plug- ins for under $200 and it will trigger on a 1 GHz sine wave.
Why pay big bucks for an interface to a junk scope get a real scope and learn how to use it.

[WD5JKO]

Right on Mark, Heck I bought a TEK 7904 with plug- ins for under $200 and it will trigger on a 1 GHz sine wave.
Why pay big bucks for an interface to a junk scope get a real scope and learn how to use it.

Yes I see the point. We all need to use a 1 Ghz scope on 80m AM! These usually cost more than a few hundred bucks the last I checked.

I have had several Tektronix scopes over the years, nothing high end, but scopes like the Tek 465, 2225, 547, etc. Of the lot the old large 547 did the best triggering on an AM envelope. I currently have a pair of 2225's used for AM. These things trigger just fine on a periodic waveform like a sine or square wave. With a modulated RF envelope the triggering is erratic, and sometimes infuriating. With my Central electronics 20A station I use the audio sample from the 20a to channel B, RF to channel A, while triggering on channel B. This works fairly well, but sometimes I have to fuss with the scope when changing the sweep time per division.

I took home from work a portable Tek with an LCD screen once. This was a digital sampling scope, about 100 mb/s I think. There was NO way this POS would trigger on an AM modulated envelope. I tried all the settings. That scope costs over $2K new too.

It is my opinion that an external scope trigger for AM modulation monitoring is the least hassle. Take it a step further and use some sort of threshold comparator to develop an external trigger that is more scope friendly, and you have a winner. I believe that this thread is about just that.

Maybe some of us can just accept that this product that Clark is using has something going for it, and for some applications that's just the ticket. Sure we can all cobble up something in a bud box as well. But how well will it work? Your mileage may vary.

Jim
WD5JKO

[WQ9E]

Jim,

Does your 2225 have a high frequency reject position for trigger coupling?  I am sure your 547 must since my Tektronix 556 (dual beam but same vintage as your 547) and the 7B series time bases I use with my 7000 series scopes all have this and it provides stable triggering on the audio component of the waveform.

I use a pair of 7854 digitizing scopes on the bench and I picked both of them up with their keyboards (needed for waveform analysis) and all plug-in slots filled for $125 each at a hamfest.  Scopes like this are excellent performers but obsolete from the industry point of view so they are cheap.  I have a 7623A  analog storage scope dedicated to a 7L13 spectrum analyzer and that pair was $300 but spectrum analyzers are still expensive