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Author Topic: running radio audio to a heathkit io 18 oscilloscope  (Read 2142 times)
CHARLESPG
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« on: August 21, 2012, 05:32:22 AM »

is there a way to run the audio  from my 857d into a oscilloscope

I have probes,but they  not will fit the audio jack


thanks

KI4VMD
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K8AXW
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« Reply #1 on: August 21, 2012, 07:41:10 AM »

CHARLESPG:  You don't say "temporary" or "permanently."  In either case you should be able to get the needed scope signal from the rear panel External Speaker jack and or the Data jack that would normally go to a tape recorder.

If this is a one-shot thing, plugging in the external speaker with the jack sleeve slid back you could clip onto the exposed center conductor and ground.  If you want it permanent then it would be a rather simple matter of either connecting permanent connections to this jack or the speaker terminals.

As for the Date jack, just wire up a suitable plug with two exposed wires for the scope (temporary) or a jack (permanent).

The scope leads can be connected with a pair of J-clamps (hook clamps) available from Jameco Electronics.  Less desirable but doable connections can be done with small alligator clips.
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AC5UP
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« Reply #2 on: August 21, 2012, 08:35:22 AM »

The Heathshkit IO-18 'scope uses a pair of binding posts for the vertical amplifier input. If a person wanted to monitor their RX audio through a 'scope like this, the first step would be to locate a line level output jack on the radio. Something not affected by the volume control and probably intended for an outboard RTTY box or similar.

Locate a matching connector for the audio port, some RG-174 (or coax like the no-name stuff used in audio patch cables), a pair of banana plugs, and a 1/2 watt 1000 Ohm resistor. Audio comes off the radio, through the cable, the 1000 Ohm resistor connects between the vertical amplifier binding posts on the Heathshkit and serves as a reasonable load impedance. Try to ensure the ground side of the signal path connects to the braid at both devices.

That's about it. Adjust the 'scope for best display. You'll probably discover "Line" for the horizontal sweep works best.

Without the load resistor there will likely be a significant impedance mismatch as the typical 'scope has an input impedance of 1 Megohm or greater and the radio is likely designed for 600 Ohm Lo-Z applications. Without the resistor you'll be looking at a distorted signal (which might not be obvious) but with a proper load what you see is very close to what you hear.

If there is no convenient line-out on the radio the next best option would be the headphone jack. Except..... The load resistor should be 25 to 47 Ohms and the volume control will need to be played with. Plus, the internal speaker will probably mute which takes all the fun out of listening to the radio. But aside from that, I'd set the 'scope sensitivity to maybe a volt or two per CM and see if the volume control comes up to less than 1/3 full throttle for a decent display height.

Your Mileage May Vary.
« Last Edit: August 21, 2012, 08:49:22 AM by AC5UP » Logged

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KA4POL
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« Reply #3 on: August 21, 2012, 08:46:03 AM »

As per page 23 of the manual you need a 3.5 mm 2-pin jack, as they call it, to go into the SP/PH jack. I'd then solder two wires to its lugs and connect them to the oscilloscope. You probably don't want to make sophisticated measurements so this will be good enough.
If you have wires with alligator clamps you can save the soldering. Just make sure you do not shorten the two outputs.
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CHARLESPG
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« Reply #4 on: August 21, 2012, 06:18:05 PM »

thanks all

I wanted to run my pc audio  into this as well
 somehow its just not getting a signal in


other then that it seems fine
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KA4POL
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« Reply #5 on: August 21, 2012, 10:01:40 PM »

I wanted to run my pc audio  into this as well
 somehow its just not getting a signal in

other then that it seems fine
You can't use the two signals in parallel. There would be different output resistances. You should be able to connect one device at a time unless the oscilloscope has two channels. Make sure you got the right plug for the PC as well. Then it must work like with the radio.
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