Ham Radio - Frame Aerial
An original Marconi Frame Aerial
Ham Radio - FrameAerial for the Medium Wave. Ham radio covers many subjects from listening to utility stations to downloading software for the digital modes but how many of you have made an aerial for the medium wavebands or the long-wave part of the spectrum.
You are probably familiar with the theory of radio waves and how to calculate wavelength and dipole dimensions but when it comes to the 150 Kilohertz band many of us would really struggle to get enough wire in the air to make a good aerial. Here is a solution to building aerials for low-Frequency ranges.
It's called a frame aerial and was used successfully when radio broadcasting first started.
Aerial for Wavelengths of 1500 meters plus are out of the question when it comes to constructing dipole but I have made many frame aerials that work very well and allow stations to be heard during the daylight hours when conditions on the medium wave and below are generally inaudible for many listeners.
I start off with a wooden frame or roughly one meter per side a piece of flat wood can be nailed to the corners at ninety degrees to help support the windings which form part of the aerial. Wind about 20 turns of wire around your frame spacing the wire a couple of millimeters apart. Aerial wire of about one millimeter in diameter is ideal for this project.
After you have wound about 20 turns terminate each end of the wire by screwing the ends into a chock-block and secure it to the bottom of the frame. The other 50 turns which I suggest you use to make your frame aerial can be added later and attached in series with the other turns; the extra turns are for greater inductance which you will need for the long wavebands.
You will also need a capacitor to bring the frame aerial into resonance on the medium wave band, I use a three gang capacitor each with a maximum capacitance of around 250 P.F. and you can wire the capacitor in series and parallel to alter the ratio for tuning purposes.
Alignment and tuning of the loop is a trial and error exercise you may need a little more capacitance when connecting your 20 turns to the extra 50 when tuning in stations on the longwave. If you place the capacitor in parallel with the turns connect a short length of coaxial cable to the same connectors the other end of the coax requires a plug to connect into your radio
You can place a single loop of wire around the frame aerial and connect this directly via coax to the receiver it works just as well, this is called inductor coupling.
Once you peak the noise on your receiver turn the frame aerial until the signal gets louder. The good thing about a loop is that it can be turned to null outstations that are weaker but on the same frequency.