This is me, on my birthday in 1959, four years before I managed to build my first (probably highly illegal) Medium Wave transmitter out of a portable transistor radio. How I managed to pull that off will stay a mystery forever. Luck was the major factor, I guess, together with some instinct. What I do remember is that I made use of the oscillator properties – tuning 455 KHz down on the transistor radio produced a carrier on the big Philips AM valve radio I had in my bedroom.
After some (even more mysterious) modifications and the addition of a very long piece of antenna wire, this ‘transmitter’ was able to serve one block of houses. I modulated the thing with a carbon microphone, which I
stole borrowed from my parents by disassembling their phone. From that point on I was hooked.
Enough is enough. I tried about every brand and model. I tried (really hard!) to modify/silence them. That worked, to some extent, but it just wasn’t enough. I still can hear these things buzzing on various frequencies. We’re not talking loud signals here, but still enough to make the life of a SWL miserable. Most people who visited me were puzzled, as they didn’t notice the interference at all. Of course they didn’t – as soon as a signal is stronger than, let’s say, S1, you won’t notice it. These people only listened to signals way above the band noise floor. I don’t. I try to detect minimalistic signals which probably would escape to the attention of most other people.
The ones I have now
The power supply I really like (if it would be silent) is the Alinco DM-330MVE. Versatile, powerful and looking great, too.
You can already spot the first hint of trouble when you unbox this PSU and take a look at the front panel. One pot, marked ‘Noise offset’ was put there for a reason – this PSU isn’t quiet. You can’t kill the interference itself, but you can move its frequency. That works, but you keep switching back and forth between the receiver and the PSU in order to get a clean signal. The interference frequencies aren’t stable either, especially when the load changes.
Personally I would like to relabel the text of this pot to ‘WCMSPS’ (We Can’t Make Silent Power Supplies). Although there are some mods available, the outcome still didn’t meet my strict requirements. Yet I won’t sell this one, as it makes a great PSU for my work bench.
The other one I own is the ‘no-frills’ Samlex SEC-1233. Samlex doesn’t try to hide the shortcomings of switching power supplies. A quote from their website:
“Switched mode power supplies (SMPS) employ high frequency switching and thus, are a source of radio interference, a recipient of radio interference and a conduit of radio interference. (Older linear type transformer based power supplies do not employ high frequency switching voltages and will be quieter as compared to switching type of supplies).”
Noise wise, this one is better than the the Alinco, especially after some mods and proper grounding. Still not good enough though. I will sell this one to someone less critical, or someone who is active on VHF/UHF only.
Back to basics
I still have an old fashioned Yaesu FP-800 power supply here, which I use now when operating on HF. I will order a Diamond GSV-3000 later this week, and put my Samlex up for sale. The Diamond isn’t perfect either – the standard rectifier diodes are not up to the task and tend to blow up after a while. Easy to fix when that happens, but I will replace them in advance.
WiFi, TV and radio signals, cell phones, even a common car key – we live in a wireless world. Most of us love it. For some, it’s bad news. A growing group of people claims to be suffering from Electromagnetic Hypersensitivity (EHS). The reported symptoms of EHS include headache, fatigue, stress, sleep disturbances, skin symptoms like prickling, burning sensations and rashes, pain and ache in muscles and many other health problems.
My first question would be “Why now?” Wireless signals been around for quite some time, and the power output of modern devices pale by comparison with the (analog) transmitters we used to have on shortwave and mediumwave. Why am I not affected, nor my fellow ham operators? Why do I have headaches and sleep disturbances when filling out a tax form, but not when I’m at a club station pumping 2KW ERP into the air? Realistically, if EHS is real, I should be dead by now. Killed by RF. Whacked by waves.
In 2005, a systematic review looked at the results of 31 experiments testing the role of electromagnetic fields in causing EHS. Each of these experiments exposed people who reported electromagnetic hypersensitivity to genuine and sham electromagnetic fields under single- or double-blind conditions. The review concluded that:
“The symptoms described by ‘electromagnetic hypersensitivity’ sufferers can be severe and are sometimes disabling. However, it has proved difficult to show under blind conditions that exposure to electromagnetic fields can trigger these symptoms. This suggests that ‘electromagnetic hypersensitivity’ is unrelated to the presence of electromagnetic fields, although more research into this phenomenon is required.”
Are you transmitting something?
So, why would I care? I’ll explain. A new neighbor, one block away, claims she suffers from EHS and got worried when she spotted my antennas. I already heard about her, so I wasn’t completely unprepared.
“Are you transmitting something?” she asked me one day. “I’m very sensitive to electromagnetic fields, you know.”
“Don’t worry”, I answered, “I have a bunch of receivers. These suck the electromagnetic fields out of the air.”
“I already thought so”, she replied. “I didn’t feel anything here yet. Pleasure meeting you.”
She walked away, happy, relieved, with a smile on her face. For a second I wanted to point out to her that there’s a 10KW digital TV transmitter just 500 meters away. I also wanted to give her the manufacturing details of the top secret device below. Fortunately I was able to restrain myself.
I’ve been experimenting extensively with this Albrecht the last few days. The verdict: this rig has potential, but needs some work. I tried to listen to my own signals at first, but that just doesn’t work. Even with the help of dummy loads, top notch receivers and headphones you can’t get a good idea of your signal quality. Many hams I asked just gave me a “5/9″, while I was almost certain that there were some issues with my modulation. I asked another (very picky) ham close by to give an opinion.
The verdict, TX
- SSB sounds distorted with the ‘mic gain’ to the max. Reducing the gain helps, but it still isn’t pretty,
- FM suffers from the same problem,
- AM sounds brilliant, almost HiFi even.
The verdict, RX
- AGC is way too fast,
- Sensitivity and selectivity are quite good in all modes,
- Again, absolutely brilliant on AM.
I will change the cheap condenser microphone for something better, and check the schematics for the AGC circuitry. Maybe I can mod it easily.
Inspired by GM4ULS, who purchased an Anytone AT-5555 for use on 10 meters, I retrieved my Albrecht AE497 from the storage and dusted it off. It’s a nice looking base station, and the power output of 25 Watts should be enough to make radio waves travel around the world. Although the radio looks more like a CB radio than anything else, two options are signs that the radio was designed with hams in mind: a 1750Hz burst tone and a customizable repeater shift.
If you want to know more, the AE497W Manual plus specs can be downloaded from this blog. I will try to hit the NYC repeater on 29.620 MHz this afternoon, and make some SSB contact as well. I’m aware that the stock microphone isn’t the best ever and sounds real tinny, but it should be good enough for a test. I’ll keep you posted.