I'm a tinkerer and a former "golden screwdriver" trucker. I've been learning to do things the right way for the last decade. I got to bore my wife with your video. And show her the 600:600 iso transformers that I got in 2 months ago to do the same thing. Thanks for making me feel smart for once.
1. I would recommend including an adequately sized output coupling cap. If there is one thing that teeny little transformers are *not* fond of, it's DC, and that includes bias supplies for electret mics. Tried it with a Behringer HD400 and a standard consumer mic input (3.3 V @ 2.2 kOhms), distortion went through the roof, absolutely hopeless. I know that dynamic mics are more common in radio, but if you're building a safeguard device anyway, I'd prefer to have that covered. 2. The whole impedance matching business would depend on whether the signal generator actually *requires* a corresponding termination for flat frequency response, which may be the case with a transformer-coupled output. Otherwise lo-Z source into hi-Z load is always fine as long as level is sufficiently high, and in case of a signal generator and a mic input I would assume it is. 3. A metal case that's left floating is not a good shield at all. A shield by definition is kept at a constant potential WRT to the circuit. Clearly that's not the case at lower frequencies when all that's keeping it tied to ground is a few pF of parasitic capacitance. 4. You oriented the transformers at 90° to each other for minimum coupling, that's something I would have pointed out explicitly. 5. If all your signal generator needs to do is put out sine waves and other predefined signals at moderate levels, you can also go low-tech and just use a battery-operated device like a phone or MP3 player instead.
Hi Mike, I think that 1:1 transfomers are technically named ”Galvanic Isolators” or ”Galvanic Couplers” but of course everyone just calls then 1:1 transformers. Just FYI. Great video.
Just as a small correction to be made (at minute-marker 4:15 to 4:25) is that "old-vintage" equipment (ie: that which contains a vacuum-tube microphone input) has a "Hi-Z" input (high impedance / ohms) and that "modern" equipment (ie: that which contains a transistorized microphone input) has a "Lo-Z" input (low impedance / ohms). >>> Courtesy of Klein Communications
It seems you do not use much video editing in your posts. I bet that saves you a lot of time in producing videos? Some "RU-vidrs" can over edit there posts. I do like your content.
I really don't do any editing. About all I do is merge video clips together. Editing takes sooooo much time to do and is something I don't have enough of.
Wouldn’t the 1:1 isolation transformer connected to coax through a BNC be an UN-UN. Unbalanced coax to Unbalanced coax regardless of frequency. Just a thought.
If you connect a jumper from your 600 ohm to your 10k ohm transformer - would that work the same as ordering a 600 to 10k transformer? The 600 to 10k are harder to find and a bit more price for them.
Hey, my friend. Send me one of those. I have another bench that I’m going to use this week and just don’t have time to order/build one. I’d live to buy one from you. What do you say?
On your Test Connector - how are you connecting for the Modulation. On the switches I see of the Original Switch -the modulation and transmit switch together,but are 2 separate circuits. I use a 6 pin momentary that will connect the 2 circuits at the same time,but yours appears to be a single on - on switch or on - off - on switch for receive and transmit.
I'm not switching the audio. The switch only switches the RX/TX circuit. If I need to turn off the audio I just turn the output from my signal generator off at the signal generator's output. Connected like I have it here you will hear your injected audio tone coming out of the speaker of the radio when your in receive on some radios. I could care less about that because the only time I have the audio signal generator hooked up is when I'm aligning the modulation circuits.
So your audio circuit is wired up direct. I was making a switch-box that could be used with a Behringer Mixer to use a Studio Mic or a regular Radio Mic,and I realized the Audio was coming through my Mic Tester without being in transmit mode. People are paying lots of money for something they can do themselves with a switch-box and a $25.00 Equalizer and a XLR Cable with a 1/4 Mono adapter.
The problem is the power supplies most people use do not have isolated outputs. Laboratory type supplies do, most power supplies intended for use with radios do not. They tie the negative to earth ground.
You can also use a three-prong to two-prong plug adapter on your signal generator. That will lift the earth ground connection on the signal generator so the ground is floating.
No, Mike is right! That’s ground loop issue, I had exactly same problem with my instruments and radios because generally the shield of input/output connector of the lab instruments are connected to the box and it to the ground wire, try yourself...
