now practice with cobra 148gtl or grant like this.
Example Alignment Using Scope and Freq Counter - YouTube
Example Alignment Using Scope and Freq Counter - YouTube
-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
New oscilloscope, does this look right?
- Thread starter 9Lives
- Start date
Ok everyone, with 1000hz tone from my Mic the first one is what I have from Am and the second from Ssb (lower I believe.)
I did some tinkering with the scope and correct me if I'm wrong but trigger its too keep the view from scrolling? In not sure what the tech term for that is?
Does this look correct? I don't even see a limiter trimmer for Am on this radio.. I see the one for ssb?
I can see with the tone the diamond shaped peaks and valleys look pretty symmetrical to me. I'm not sure what it's supposed to look like on side band.
Please everyone give me your constructive criticism as quick as possible, I'm going to leave it hooked up for now but I want our back in the truck tonight.
It's this the best I can do without npc? If I do the Npc what can I expect? Also one last question, should I lower the resistor on the carrier (am power) trimmer resistor to go even lower? I can really tell but I think it's less than 1 watt. Should I be higher when driving 2x 2sc2879 at 14.2 volts (roughly where it stays)
I did some tinkering with the scope and correct me if I'm wrong but trigger its too keep the view from scrolling? In not sure what the tech term for that is?
Does this look correct? I don't even see a limiter trimmer for Am on this radio.. I see the one for ssb?
I can see with the tone the diamond shaped peaks and valleys look pretty symmetrical to me. I'm not sure what it's supposed to look like on side band.
Please everyone give me your constructive criticism as quick as possible, I'm going to leave it hooked up for now but I want our back in the truck tonight.
It's this the best I can do without npc? If I do the Npc what can I expect? Also one last question, should I lower the resistor on the carrier (am power) trimmer resistor to go even lower? I can really tell but I think it's less than 1 watt. Should I be higher when driving 2x 2sc2879 at 14.2 volts (roughly where it stays)
The waves in this picture don't look like symmetrical sine waves.
Are you using a 1khz sine wave audio source into the mic?
Should look like this:
Ahhh . . . The million-dollar question . . . Afraid the answer is far more complex than the question . . .
Try another radio and see if the problem is in the scope - or in the radio. Could even be the way you have the scope hooked up. What are you using to sample the signal into the scope? Are your hookup/BNC cables in decent shape w/o being intermittent?
Last edited:
Check your ground leads on the probe as well. Also check and see if the probe you are using is a 10:1 voltage divider probe. Most have a small trimmer in the end that plugs into the scope that adjusts the shape slightly. Usually you connect it to a squarewave signal source and adjust for a smooth flat top with no rounding on the corners. There should be a squarewave output for testing right on the front of the scope itself.
Well... hmmm..I used 20x 1k 1 watt 1% metal film resistors to make 50 ohm 20 watt d load, I have that on surface mount copper clad,I made this, it's inside a Hammond enclosure. The rf sampler.. lol is on copper clad, 2 ge diodes opposing to gnd, into 7pf into 47 ohm resistor into the other half of a cut bnc 50 ohm cable.. problem is, it's hanging from the cable from the d load not enclosed.. that could be the problem, but the power supply its a pc supply, not the best I know but it's all I got for now, I made an amc circuit trimmer bc this radio doesn't have one, it seemed to distort the signal more than help. I used a schotty diode tho, maybe not enough drop??
I also lower the resistor coming off the am power to 1k2. For better control of the carrier, . I might attempt the amc one last time with a regular switching diode..
I've heard of people lowering r131, will this get some more peak through?
I also lower the resistor coming off the am power to 1k2. For better control of the carrier, . I might attempt the amc one last time with a regular switching diode..
I've heard of people lowering r131, will this get some more peak through?
It doesn't look too bad, as far as AM goes. The lobes "leaning" can be caused by what Robb mentioned, also possibly how purely your 1khz tone is generated. If the 1khz tone isn't totally clean (ie. other tones, etc) it can cause the waveforms to lean or distort too. Below is a couple of pics I snapped of my O'scope.
The 1st pic is a Cobra 2000 GTL with R131 removed, it disables the AMC. You can obviously tell that it's nasty, squared off, flat-topping, etc.
The 2nd pic is with R131 replace and properly adjusted to 100% modulation. I used my B&K 1040 Servicemaster to generate the 1khz tone.
Hope this helps!
(edit) The 2nd pic is a little on the fuzzy side, didn't give the camera enough time to re-focus. I apologize!
~Cheers~
The 1st pic is a Cobra 2000 GTL with R131 removed, it disables the AMC. You can obviously tell that it's nasty, squared off, flat-topping, etc.
The 2nd pic is with R131 replace and properly adjusted to 100% modulation. I used my B&K 1040 Servicemaster to generate the 1khz tone.
Hope this helps!
(edit) The 2nd pic is a little on the fuzzy side, didn't give the camera enough time to re-focus. I apologize!
~Cheers~
You don't need the sampler.
Disconnect the sampler so that it is not involved with the circuitry.
Just hook the x10 probe to the input of the dummy load.
Put the attenuator selector knob so you have 10v division sensivity.
From there you can adjust the input sensitivity to suit the size of the display area of the screen.
Make sure that you have a x10 scope probe. ( you don't want a lot of rf going into the input attenuator on the scope )
You might need a sampler or signal attenuator at a later date if you start testing 100 radios or linears. ( but then you will need a bigger dummy load, too )
If you don't use an attenuator for hi-power measurements you can toast the compensating network in the x10 scope probe.
Last edited: