Clean RF RF demodulator.

[K5UJ]

<<<4XX series had problems with transistor sockets. Best way to fix the problem is to solder the transistors into the socket.>>>

Thanks Frank, I have two of those.  I thought the transistor sockets were a nice feature   I hate to solder them; maybe I'll re-seat them if there's a problem.  

Clark, what are you talking about?

You must be asking about the SWR bridge mod.  Go back and read my earlier posts.  If you are asking for a schematic diagram the "design" is so simple it hardly needs any diagram.  Get a elcheapo SWR bridge, the kind that inserts in an unbalanced feedline with a meter and a "forward/reverse" switch.  They have a meter set pot.  The idea is that you transmit a carrier and adjust the pot so in forward position the meter reads full scale. You flip the switch to "reverse" and read the line SWR.

Well, the bridge has a couple cheap glass diodes that rectify the picked up RF to drive the meter movement.  They are connected to the wiper on the pot via the switch.  That's your rectified RF.  You need only drill a hole in the cabinet, insert a jack (BNC or RCA phono work best) and run a short jumper from the jack center to the pot wiper.  use some kind of coax jumper from that to your scope trigger.  That's the "design."

For pickup of the RF you probably have that taken care of.  I didn't even bother making a probe box; I simply used an available jack on a feedline coax switch.  The isolation is good enough so I get enough signal to see without blowing anything and I have it arranged to prevent accidentally transmitting into the scope, which would be a real bummer if it were to happen. 

My first scope was an old Tek 475 I got from work for fifty bucks.  I did not know it at the time but it was not in very good shape and this is what I tried to get a stable display.   I still use that scope to see received mod. envelopes via an IF tube tap on the 75A3.   It is tricky because I only have the signal to trigger on so I have to get it just right and Ioose it if the amplitude drops. 

Rob

[ke7trp]

Rob. You are being combative for some strange reason. You spoke of a better design that was cheap. I would like you to design something for us so we can all use it. If you cant do that. I understand.  Sorry.

C

[WA1GFZ]

Rob, think about it, how often does a transistor wear out in a well designed circuit? the 4XX series was just after the tube days. Another problem was many of the transistors had the leads cut too short. Early 4XX series were the biggest problem. If a transistor ever fails it isn't a big deal to desolder it.

[K5UJ]

Frank, good point.  right after tubes; short leads...

Rob. You are being combative for some strange reason. You spoke of a better design that was cheap. I would like you to design something for us so we can all use it. If you cant do that. I understand.  Sorry.

C

Clark,  I can't imagine how I seem combative but I assure you that could not be further from my intent and I sincerely apologize--I would like to be able to have a friendly QSO with you some day on the radio and consider you a friend like everyone else here.  Please go back and carefully re-read my earlier messages.  I never claimed to have anything I thought was better as a design--cheaper yes--in fact I think I even wrote that your product might be better.   In the long run we're just talking about a mod envelope on a scope.   It's really not a big deal.  Please enjoy your boxes and God bless you.

Rob

[ke7trp]

Back in the first page you talked about building something cheaper that would work. I asked you to show us.   Sorry if I came off rude or anything.

C

[w3jn]

Clark, Rob described his box in the first reply to your initial post.  Not sure why you're getting spun up about it and demanding that Rob design something for you.

This is a hobby, and there's room for all manner of ways to do things.  Don't take someone else's method as a challenge to your way.  If you like it and you're having fun with it, that's what it's all about 

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]

I am not getting spun up.  He told me he could make something better for next to nothing. So did HRO. But then they never posted how.  I wanted to learn how...

The trouble with suggestions here is that it will blow up headphones.  Using the diode for the audio wont work as its not filtered.  Try that with a high power transmitter and see it smoke your nice headphones.  Raw DC.  Been there done that. It would be nice if someone puts out claims, they actualy show us how. Cause Rob told me that he could make this for $20. I just want to see that. I need about 5 of them. One for each transmitter!

Cya and sorry if I came off the wrong way. Sometimes its hard on text to judge how someone is acting.

Clark   

[WA1GFZ]

The problem with the 4XX series transistor sockets was the  contact plating wore off from the motion of going in to wiggle each one trying to bring it back up. I remember the cal lab guys at one job having fun with these scopes.
Outside of the transistor socket problem they all were very good and a lot easier to lug around than the 5XX tanks. 

[ke7trp]

HRO.. I tested this with a modern scope and the old Tek 422.  The modern scope without the trigger input is not nearly as stable as using the trigger.  The reason I believe is that you are sending base band audio to the scope directly as the source.  Also. The outputs for audio are DC blocked and filtered. 

Cya

Clark

[ke7trp]

Oh.. Sorry for the confusion.  Above in the thread it was suggested that if you had a modern scope, You dould not need this.. Only the RF pickup. I guess I got confused. I had my friend bring over a 350mhz scope and we could not produce the lock on the envelope like we can with the Clean RF Trigger.

Clark

[w3jn]

Did the scope have the "HF Reject" feature in the trigger circuit?  Most Tek scopes and even that POS Gould I have has this.

[WQ9E]

JN,

The only Tek scope I have without HF reject is a type 514AD that belonged to my father.  It has a specified bandwidth of only 10 Mhz. and a somewhat touchy and awkward trigger/timebase system.  However, it does provide direct access to the deflection plates for high bandwidth applications.   My father used this to teach me how to calibrate scopes when I was 14 and I cannot remember how many iterations I made through the vertical delay line procedure until I finally got it right.

Did the scope have the "HF Reject" feature in the trigger circuit?  Most Tek scopes and even that POS Gould I have has this.