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Author Topic: HTX 202 to MFJ 1278 TNC Connection question  (Read 899 times)
W4KYR
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Posts: 568




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« on: January 20, 2013, 07:59:50 AM »

Radio Shack HTX 202 to MFJ 1278 TNC Connection question

 I have Googled the question and have come up with two different answers. I want to hook up the HTX 202 to the MFJ 1278 TNC.

One answer says I have to use a 1:1 audio transformer, a resistor and a capacitor in between the connections between the two. (Why?)

However the RS HTX 202 owners manual mentions no such thing and looks like a simple matter of just hooking them up. Now I don't have the resistor, capacitor or the audio transformer. I could order them. But it would be easier for me to just use another radio in the meantime.

1. So do I just hook them up without the extra parts like the owners manual says?

2. Do I need the extra parts so I don't ruin the radio or the TNC?

3. What other radio could I hookup to the MFJ 1278 without ordering extra parts?

4. Does anyone have a simple diagram for hooking up a radio to the MFJ 1278?

I will be using hyperterminal for what it is worth. I eventually want to make all 'old school project" (using vintage 1990's equipment for packet).

Thanks

« Last Edit: January 20, 2013, 08:05:56 AM by W4KYR » Logged

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N3JBH
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Posts: 2358




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« Reply #1 on: January 20, 2013, 08:50:11 AM »

Only thing i see you might need be a 2.2K resistor on pin 3 of the mic connector and radio shack sells them in a 5 pack for $1.20  so that should be easy enough. I have no idea what you really need the transformer for. And i do not think there is voltage on pin 3   If there is that explain the cap that be a easy test to do.
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KE3WD
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« Reply #2 on: January 20, 2013, 10:54:13 AM »

Use of audio isolation transformer may or may not be needed, depends upon particular situation and how the chassis grounding is handled.

Start without the transformer, if you encounter noise, hum, etc. on the signal, that may be indicative of the dreaded Audio Ground Loop situation, adding the transformer will take care of the problem if it rears its ugly head. 


73
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W4KYR
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Posts: 568




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« Reply #3 on: January 20, 2013, 12:13:25 PM »

OK thanks for the replies. I'll take a ride over to Radio Shack to see if they have the parts. I didn't think shack still sold resistors and capacitors.

Thanks
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