Foundations of Amateur Radio

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Checking your On-Air signal...

Posted: 11 Mar 2017 09:00 AM PST


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...
This posting includes a media file:
http://podcasts.itmaze.com.au/founda...teur-radio.mp3