Checking your On-Air signal...

Foundations of Amateur Radio

The other day I managed to achieve a little personal milestone. I heard myself on-air. Before you get all misty-eyed, yes, I've heard myself on-air before - probably on thousands of occasions over the years, but that's not what this was. This was my own transmitter, in my shack, transmitting my voice via SSB and it being received and me hearing it.

In broadcast radio this is a common thing. Every radio station I've ever been in pipes the audio from a normal radio receiver into the studio, so you can confirm that your transmission is in fact going to air as expected. There are funny stories associated with experts who decided that they didn't need to wear headphones and promptly broadcast silence because their microphone volume was turned down or not plugged in - gotta love the helpful announcer in the previous shift.

So, what was so special about hearing myself this time?

Well, for the first time I heard my SSB voice. Not AM, not FM, SSB. I'd tried this before using two radios and a dummy load, but that just ended up in distortion, not much fun.

Let me tell you how I managed this and what I learned along the way.

Online I found a local Software Defined Radio, or SDR, that had the ability to tune to a frequency that I am allowed to transmit on. That seems pretty straightforward, but in actual fact getting those three things, Online, Local and Frequency all together has proven to be a bit of a challenge.

I started listening to the station to see how their signal compared to mine. I have a project sitting on my shelf to put together my own SDR, but that ran into some procurement issues, so I've been limited in my ability to experiment.

I started out trying to listen to the local HF beacon, part of the Northern California DX Beacon network. Turns out that the SDR and I can hear that pretty equally.

I did notice that there was about a five second delay between what I heard off-air and what the SDR sent to me across the Internet. I don't know if the delay is because the Internet signal travelled back and forth across the country a couple of times, or because this particular SDR has some delays.

I tuned the SDR to 28.490 and my radio to 28.490 and after checking if the frequency was in-use started some test transmissions. Nothing was working. No noise, nada. It does help if you plug the right antenna into the radio. Tada, look Ma, it makes noise! I could hear myself.

It became clear that there was a difference in what I was expecting to hear and what I actually heard. Playing with different modes didn't seem to make any real difference, so I was a little stumped.

I recalled that during a contest I had been advised that I was off frequency, so I played with my Tuning Dial, known as the VFO, and adjusted my frequency to 28.489.50 and there I was, just like I expected. Five second delay and all.

At that point I wondered if this meant that the SDR frequency was wrong, or mine, or both - how could I prove it? Some hunting around for suggestions revealed the idea of tuning the SDR to one of the time frequencies, on 5, 10, 15, 20 and 25 MHz, better known as WWV and WWH. On these frequencies a 24 hour a day transmission happens that encodes the time. You'll hear a ticking clock, voice indicating time and it has all manner of extra information encoded in the signal. It's used as a time standard but also as a frequency reference. Best results are when you use AM and you can use it to get a sense of propagation between you and Colorado in the United States. Mind you they are using a few extra Watts.

Zooming right in I could see that the SDR was indicating that it was bang on frequency, so I'm about 50 Hz off, high as it happens. Which just means that I need to tune a little lower than the frequency I want to be on and I'm good to go.

Only I'm not yet convinced.

I came across settings on my radio, the TX Carrier Point for USB, menu 18 on my Yaesu FT-857d. Other than various wild guesses by others, I still don't know what it actually does, all I do know is that it was set to 150 Hz. Setting it back to 0 didn't make the problem go away, but it did appear to improve things.

Not sure yet if my radio is in need of a doctor, or if I am in need of some instruction, either way I'm sure you or a friend knows and is willing to share.

Turns out, I sound just as sexy on SSB as I do on FM. At least my wife thinks so.

I'm Onno VK6FLAB.