Saturday, August 30, 2008

Monitoring the Gulf Coast Hurricane Net

One of the more interesting aspects of amateur radio for me has always been monitoring the Gulf Coast Hurricane Net when there was a storm threatening the Gulf Coast area. As of Saturday evening, the net is active on the following frequencies:

Central Gulf Coast Hurricane Net
Daytime Tactical: 7.285 Mhz
Nighttime Tactical: 3.873 Mhz

Daytime Health and Welfare: 7.290 Mhz
Nighttime Health and Welfare: 3.935 Mhz

Sunday, August 10, 2008

Tracking down the elusive electrical noise in my home

I have finally found the annoying “mystery noise” I’ve been hearing on HF (mostly 75 meters) today. I first begin to hear the noise after I moved my Yaseu 857D from my outdoor (not air conditioned) ham shack to the comforts of a spare room in my home. While it is great to have the space (and air conditioning) I immediately began to hear a crescendo of noises that sounded like “birdies” or raspy “carrier like” noises. In one case the noise appeared every 100 KHz pretty much from the broadcast band to 10 meters!

I first had to determine if the noises were radiated signals or were, instead, internal “birdies” sometimes heard from receivers of poor design The way I did this was to switch the 857 to dummy load and verify I could still hear the noise – I still heard it even though it was somewhat weak.

The next step was to determine if it was an internal “birdie” from the 857 or a radiated signal. By disconnecting the HF antenna all of the noise disappeared so I was pretty sure it was not a birdie.

At this point I became convinced the source of the noise was something electrical inside my home. I powered up the 857 from a couple of AGM batteries and tuned the VFO to a spot where I could hear the noise quite loud. I then went to my power switchbox and tripped the main breaker.

What do you know – the noise went away! In fact, I’ve never heard the band so quiet!

After I turned the main breaker back on it was just a matter of tripping the individual breakers until I found the offending circuit. Turns out the noisy circuit was one feeding one of those “touch lamps” – the kind where you touch the metal lamp base and the bulb steps thru three levels of brightness. Those things are awful noise generators! I unplugged the lamp, put the breaker back on and listened to verify the noise was gone. Thankfully it was. But, then I heard yet a different noise which I quickly tracked down to a horizontal sweep signal from the TV upstairs.

That was easy to fix -- just turn off the TV.

But wait – I was hearing yet another raspy noise on the frequency. This one was a little harder to find but it was definitely man made inasmuch as it appeared on even frequency multiples across the band. I suspected the source to be a switching power supply, perhaps my UPS or maybe even the laptop computer itself. It took a while to pin it down but when I unplugged the laptop charger the noise went away – and resumed when the charger was again connected to the computer. It didn’t matter which end was unplugged, the AC supply end or the DC cable at the computer.

So, now I am finally happy. I have found the offending noise and those I can’t eliminate at least I know what to turn off should I want to listen to the same spot on the dial where these local oscillations are occurring.

In most cases it would not even matter but this morning the touch lamp was just tearing up the Georgia Cracker Net on 3.995 MHz and that is what got me started. I would have probably just written it off as a distant carrier on the band but because I was able to listen to my friend Lyndy’s Brannon’s station via his streaming audio setup I knew it was not affecting the entire net – It had to be something local.

Friday, August 8, 2008

Blown VHF Finals in a Yaseu 857D

I am officially a member of the infamous "Blown Finals Club" of Yaesu 857 and 817 owners.
Today, after a $230.00 repair bill and FedEx shipping both ways I have my radio back from the Yaesu Service Center in California and other than a huge void in my wallet, life is good once again.

So how did this happen?

I'll never know what caused the final VHF transistor and several capacitors to suddenly fail but at the time I was using the radio to transmit thru a 45 watt in - 170 watt out linear amplifier. The antenna is a 2-meter 5/8 wave ground plane that I've been using for months. Likewise, the 857 has been transmitting thru this amplifier for many months though the amplifier is almost always off.

This time I was transmitting about 45 watts FM on 146.52 into the amplifier (now switched on) and carried on a simplex QSO for a few minutes. We then switched to 144.20 SSB and continued the QSO briefly. I was still using the amplifier, only this time the rocker switch was switched to SSB. Having an unsuccessful QSO I switched the Yaesu 857 back to FM and changed frequency back to 146.52. I keyed the mike and became aware that I was not transmitting. I noticed the amplifier was still switched to SSB so I flipped the switch on the amp back to FM. Still no transmit power from the 857.

I tried several tests in various configurations, first without the amplifier. I found that I was actually able to be heard on the local repeater although I was reported quite noisy. This led me to conclude that I was transmitting with at least the driver stage of the transmitter. I switched to a good dummy load and then monitored my 2-meter transmissions on a VX5R handheld I had in the shack. Everything sounded well -- good audio etc.

At this point it became painfully obvious I had a blown PA transistor. By the way, the radio continued to function properly on the HF frequencies. Only 2-meters and above were affected.

I carefully packaged the radio in its original box and with a humble letter enclosed I sent it on its way to the Yaesu hospital in California.