I have a nice B&K 35 mhz that I would like to use on my cb work. So far I have been using my Dosy psw-4002, Conar frequency generator, Astron VS-35M and a palstar 1.5Kw. I also have a vintage Wawasee jb-1002 that I primarily use to check frequency. I have some new 1x and 10x probe with BNC connector. Need some hints on how and were to hook modulation and the scales I should use and any resistors in line at the speaker connection if any. I also have a BNC with a coaxial end to insert into the back of cb(PL259). I dont know what and if my scope can handle the power output of radio directly into the scope or does it need an attenuator. Sorry for the stupid questions, but trying to figure out one my own. Any help would be great. Thanks.
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Need help with oscilliscope hook-ups for cb
- Thread starter Cityboy
- Start date
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BOOTY MONSTER
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i certianly cant help with your questions . but if you dont have the manual heres a link to the manufacturer .
I too have been looking into this. From what little I know on this topic, I believe a RF Sampler would be the best approach. I hope to build one once it thaws again in the garage. This example comes from a HyGain svc manual and I've been told it too should work for a scope in addition to the freq counter set-up it was designed for. There are other plans out there if one searches. Commercial assembled units are beyond my current budget. Hope this helps.
Thanks for the suggestion so far; especially freecells' link to the oscilliscope handbook. I know how to measure the most of the basics, the main thing I was looking for is hooking my scope to look at modulation of the cb, and where exactly to hook the probe(like does the ground go to the - side of speaker terminal or chasis, does the + probe go to the + terminal of speaker). I will dabble into measuring voltages across the circuits for troubleshooting later, but for now I just wanted to be able to set the modulation using the scope and to check my setting of the recieve. If you can specifically tell me where to hook to and settings of the probe(1X,10X) and anything I would need to make these basic measurements I would appreciate it. The other big question is what kinds of or can you even hook the bnc connector with the PL259 end to it directly to the radio and key it up. For I am not that familiar with whether you can load the scope up with a key up from the radio or do I need an attenuator. Please help the idiot; I want to learn but would prefer not to blow up my equipment.
If you're trying to see the modulation level of a transmitter, you certainly don't need to worry about connecting anything to the speaker unless the speaker also serves as the microphone.
I'd also recommend against connecting the full output of any transmitter directly to the input of any o'scope.
I'd also recommend against connecting the full output of any transmitter directly to the input of any o'scope.
Look at the diagram above again. You would view the modulation from a sample of the radio's RF output, while keying the radio.
As stated by others previously, you should not attempt to measure the output without tempering the signal by means of a RF sampler.
As stated by others previously, you should not attempt to measure the output without tempering the signal by means of a RF sampler.
I made an RF sampler a few years ago for the same purpose. It's really simple. Here's how you do it:
http://www.worldwidedx.com/home-brew-mods/32110-rf-sampler.html#post128499
http://www.worldwidedx.com/home-brew-mods/32110-rf-sampler.html#post128499
Thanks for the replies, and its is finally getting through my thick head that the rf sampler/demodulator is what I need. Thanks once again moleculo for the pics and I assume the 2k resistor and is grounded behind the nut and washer of the so239. I can get all of the supplies I need including the project box at rat shack correct? Thanks once again and I sure I will need more help. I was very confident that I should not connect to rf power directly into the scope; I knew it wouldn't be able to handle the power. Thx
Sorry, about that I didn' really look at it; I just quoted what bootymonster said. I should of looked at it. Is that a 1 watt or 1/2 watt and how much power can it handle. I do work on some exports that put out quite a bit of power. I am a little confused about the rf sampler though. I assume one coax input comes from the transmitter to one of the coax inputs and the other is going to go to my meters and dummy load, correct. The bnc I will guess is an output sampler that goes directly to the scope, is that correct? So I will need a bnc to bnc cord to make this work, or am I missing something thanks. Dave.
I think that resistor is a 2 watt resistor. You won't have a problem with the exports on it. You can sort of see it in this picture here. I hook up the subject radio to the coax that feeds into the Bird43P. The RF sampler is attached to the output of the Bird and feeds through to a dummy load. I T'd off of the BNC connector on the RF Sampler to feed into the O-Scope and the Frequency counter. So with this setup you can key the radio and see the power output on the Bird, the O-scope, and the frequency all at once.
Thanks alot moleculo; I will build one as soon as I have time and get the parts needed. I have the so239 input,outpu; I just need some bnc connectors and a 2 watt resistor and a ferrite core and a bnc to bnc connector cord. I assume I could make my own, could I use regular RG8 coax and solder bnc connectors on it. Thx.
BNCs are primarily intended for RG-58/59 size coax. They're pretty small. I'm sure that Amphenol makes a version to go on RG8, but that's a heavy cable for such a small connector.