The heyday of AM radio is long gone. The image of an attentive Mets or Jets fan listening on a small transistor radio is now part of a fading Life magazine.
In Europe the transmitters are slowly being turned off and here in the US, AM is a strange world of hardened political talk, unique religious views, occasional news and seemingly lots of south of the border music.
Mark Hilbert, our local philanthropic promoter of all things California art, seems to have a thing about the art of AM radios.
It’s not very hard to get me excited about anything radio. Seeing Hilbert’s radios, had my prepper AM radio out one night and I happened upon the barely audible AM 650 from Window Rock, AZ over 500 miles away, I was curious to see if I could do better and hear all things Navajo.
Not the ugly duckling to me
Antennas come in all shapes and sizes, generally larger than not, generally gangly and occupying a lot of space and seemingly with a correlation between bigger and better. Except one, a loop in the special case of receive only.
Benign nulling, sinister nulling
Loops have remarkable properties for the job at hand, nulling. A loop’s shape enables the antenna to be directional and in effect “favoring” signals from certain directions while simultaneously dampening (nulling) those from other directions. Remarkably useful in of itself, it has another nulling trick when built the way I intend to build it. The second results in a loop “hearing” signals better at one specific spot (say 880 AM) on the AM dial but pretty much nulling out all adjacent signals say 550-850 and 900-1700).
Great for what I want to do, find “weak”, masked by strong local stations that are on a specific compass bearing to my location.
The down side is two or three radios doing this simultaneously enables pin pointing a transmitter and if you’re a freedom fighter in say occupied Europe you may find dark forces at your door moments later.
A celebration of physics
Unlike a possible modern solution these are the model of simplicity. Two passive components (i.e no power required for a loop to work), an inductor (part of a family of passive analog components like a resistor, wire, capacitor etc) and a variable capacitor.
My inductor is simply eight turns of very thin metal wire. To support these, I used 1/2″ PVC irrigation tubes. Each arm is 18″ for 3 feet (1m) wide and the same tall. 8 turns of wire amounting to around 68 feet maybe 20m in total.
Hammarlund….retro treasures
In the rapidly decaying world of pure analog radios, one collectable is much sort after, the variable capacitor. American companies long bankrupt or long merged such as Hammarlund made them.
Everything is a journey
Size matters and the 1m/3ft wide prototype, as fun as it was to build and in some respects more mechanical/construction centric than I thought, should be super sized!
Why not 6ft (2m) wide hoisted up to 20 ft (6m) ?
A small monster that can sit atop my Yaesu rotated SpiderBeam mast. Not quite reusing stuff from the “junk” box but definitely nothing new required to make it happen beyond 1″ wide PVC.
Varactors….one of those 1950s semi-conductor marvels and an almost “only in America” innovation, lends itself so well to replacing the Hammurland capacitor. As a plus it requires software, an area I know better to add capacitance.
Dyed in the wool “maker”
I love making things.
The sense of accomplishment is real, the sense of learning is real and the sense of time not wasted is real. This was a project I never planned and amongst other things reminds me that life’s small surprises can be quite memorable.
Oh…. and one other thing that is memorable….maybe it’s “Regina Cole” that announces the weather from Lincoln, Nebraska on KRVN. Either way, hearing the female meteorologist annunciate “KRVN” and “.com” made me chuckle, almost like something from the movie “Fargo”.