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Old 19th Jun 2020, 10:42 am   #1
Radio Surfer
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Default Correct leads, connections and adapters

Morning,

I hope this is the correct section for this embarrassingly basic query, so please don’t roll your eyes too much.

I’ve recently acquired a frequency counter (Apollo 100) and, having viewed various video clips, wondered how this should be connected to a function generator and oscilloscope (Tektronix 465B) to avoid loss of signal, distortions, reflections etc.

The videos I’ve watched are very good at explaining how to use the equipment but always seem to bypass the key point of how they should be connected. I see what appear to be simple bnc to bnc leads from generator to oscilloscope or counter, T shaped splitters used with leads flying off to the counter and scope, but won’t this give reflections, phase differences, misleading readings, particularly at higher frequencies?

The frequency generator doesn’t have a digital readout, hence the counter. So I would like to set an output on the generator, have the reading on the counter and display the image on the oscilloscope. Pretty basic stuff, but can’t find any real consistent guidance/advice on the best/correct way to connect this up. The maximum frequency would be 25Mhz.

Many thanks, Richard
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Old 19th Jun 2020, 11:13 am   #2
Herald1360
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Default Re: Correct leads, connections and adapters

Provided that your BNC leads to the 'scope and counter are short compared to wavelength (12m at 25MHz) and the counter input is hi-Z it should just work OK.

If you want "perfection" you'll need a 50R splitter and 50R loads at the counter and 'scope and equal length leads from the splitter to the counter and 'scope and you'll have to factor in the splitter loss for 'scope amplitude measurements to be meaningful......

Have fun!
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Old 19th Jun 2020, 11:26 am   #3
barrymagrec
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Default Re: Correct leads, connections and adapters

You should have a vertical signal out socket on the back of the 465B - you can connect this directly to the counter and it should read the frequency of whatever signal you are inputting to channel 1.

Failing that you should use a BNC T adaptor on the scope input and connect one side to the generator and the other to the counter, ideally terminating at the counter with 50 ohms.
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Old 19th Jun 2020, 10:27 pm   #4
PETERg0rsq
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Default Re: Correct leads, connections and adapters

As with everything else, it all depends on what you want to measure.

Measuring RF is full of difficulties and complications, untill you understand what you want to measure.

You do not mention what signal generator you have, and if the output is high impedence, or 50 ohms.

Assuming it is 50 ohms (most RF generators are), you can just connect it direct to the oscilloscope, but make sure oscilloscope is set to 50 ohm input also. This will give the most accurate display on the scope (But remember all measurements will be only valid for a 50 ohm system!)

You can then Connect the counter to the coax via a T piece, but make sure you are using the high impedence input to the counter.

If the counter only has a 50 ohm input impedence, then you can not connect this way and keep accurate display on the scope. You would need to fit a series resistor in the counter lead to increase the impedence to a few hundred Kohm minimum, but this would reduce the sensitivity of the counter.
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Old 20th Jun 2020, 7:45 am   #5
Radio Surfer
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Default Re: Correct leads, connections and adapters

Morning,

Thank you for the above responses, that has helped my understanding and given me some options to try. Given the limited leads and connectors I currently have ( why is it when you buy used stuff there are never leads) I’m going to utilise what I have to begin with. So I’ll connect the generator to the scope with the scope probe and a probe to BNC adapter and then a BNC lead from the channel 1 out at the back of the scope (thanks for that tip) to the counter. I’ll order a BNC T splitter and in-line 50 ohm termination over the weekend so I can try the alternative approaches above and compare the results.

One other question, with a BNC T splitter, when you are not using one side of the junction should you use a proper termination (blank) rather than just leave the socket “exposed”? If so, I’ll order one of those as well.

Many thanks and all the best, Richard
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Old 20th Jun 2020, 9:58 pm   #6
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Default Re: Correct leads, connections and adapters

Hello,

I’ve answered my own query, the penny has just dropped whilst gardening and some basic school boy electronics came back to me. I’ve ordered some BNC cables and terminators of various values so that I can experiment and prove I’m not as stupid as I first thought.

Thanks again,

All the best Richard
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Old 22nd Jun 2020, 12:10 am   #7
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Default Re: Correct leads, connections and adapters

Well done.

Just keep asking questions.
We ALL learn, layer by layer.

Good luck.
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Old 29th Jun 2020, 1:48 pm   #8
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Default Re: Correct leads, connections and adapters

Hello,

My leads, various connectors and terminations arrived over the weekend and as its blowing a hoolie outside, its a good excuse to test things out.

I’ve tried different ways of connecting the generator, scope and counter together based on suggestions here, with different terminations etc. and settled on one that works for me and seems most logical and all seems fine. The results come out as I’d calculated, so I must be learning!

I’m still only playing and learning how to use the kit at the moment. A few good things; firstly all the stuff works and gives the expected outcome, the readings from the scope and counter are consistent with the output from the function generator as can be seen from the photos ; secondly the cost of the leads and connectors etc. have been almost as much as I spent on my 3 pieces of equipment so far which I suppose isn’t a bad thing. I’ve risked bargain stuff or virtual giveaways that were either reluctant to work or just looked a bit sad, covered in PAT, calibration and asset number stickers, missing feet, dirty, bent cases, covered in dust and dirty switch contacts etc. etc. and been very fortunate they have come out really well. If my labour was included they would have cost a small fortune!

Thanks for the advice so far on my retro kit which now comprises:

Tektronix 465B
HP 3312A Function Generator
Apollo 100 Universal Timer-Counter
AVO 8 mkIII, and the smell of that takes me back to physics lessons at school.

I wonder what’s next?

All the best, Richard
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Old 29th Jun 2020, 2:48 pm   #9
dave cox
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Default Re: Correct leads, connections and adapters

Your scope has a vertical out socket on the rear - this can probably be connected to a counter. A caveat with doing this is that it will only work properly (if at all!) when displaying a single trace due to beam multiplexing. Its worthwhile looking up the specification of the signal here but I doubt that there will be any problem connecting a counter, 50ohm or otherwise.

dc
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Old 2nd Jul 2020, 12:09 pm   #10
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Default Re: Correct leads, connections and adapters

#3 above.
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