Converting an AM broadcast receiver to hear 160 metres
There are several ways to start tuning in to 160 metres.
You can either modify an old AM transistor radio, buy a special 'communications
receiver' or make your own. Modifying an old radio is easiest and cheapest, so we'll
start with this first.
Getting started: obtaining an AM radio
Almost any portable AM broadcast radio can be made to receive 160 metres. Find a battery powered one
with an old-fashioned tuning knob and dial; digital tuning radios are no good. If you don't have one, try garage
sales and swapmeets. Radios made in the 1960s, 70s and early 80s are best. Medium-sized portables go better
than pocket or clock radios. FM is not needed. Pay no more than $10.
The hard bit: doing the conversion
1. Find out when 160 metres is most active in your area. WIA broadcast relays or other long transmissions are best. In Melbourne the 11am Monday - Saturday 'Coffee Break' net is suggested.
2. Disconnect any mains power leads.
3. Remove back with screwdriver and insert batteries.
4. Find a weak AM station near 1600 on the dial.
5. Identify tuning capacitor. This is the plastic box on circuit board approx 25mm square.
Note the small screwdriver slots that you will be adjusting.
6. With set operating adjust the tuning dial to read slightly lower so station sounds distorted.
7. With a small flat-blade screwdriver adjust one of the screwdriver slots. If nothing happens
you've found slots for FM or shortwave – leave these alone. If the station gets weaker,
but stays distorted you've located the 'front-end' tuning – take note but leave alone for now. If the
station gets clearer, but a slight adjustment the other way makes it vanish, you've found the
'local oscillator' adjustment, which is what we need. Again set the radio dial lower and re-adjust
the local oscillator to bring the station back again.
8. Repeat until your chosen 1600 kHz station appears near 1450 on the dial.
9. Move dial to near 1600.
10. With screwdriver adjust 'front-end' tuning setting for maximum noise out of radio. You will notice that
adjusting moves some tiny metal plates on this component, which is called a trimmer capacitor. When
you see a semi-circle all plates are overlapping and the capacitor is at its maximum setting. When plates
are not overlapping, you will see a full circle and the capacitor is at minimum capacitance.
11. Tune around for amateurs. Amateurs will be using frequencies up to about 1850kHz, but because we have adjusted the insides of the radio, they will appear near 1600 on the dial.
12. Re-peak 'front-end' tuning for maximum strength on these signals. Because higher frequencies require less capacitance, the trimmer capacitor's plates will hardly be overlapping. If there is no overlap at all (ie full circle)
the radio may not be adjusted for peak sensitivity. Refer to the optional step 13 for a way to get around this.
13. (optional) If receiver sensitivity is still poor, and you can't hear noise out of the radio even when the volume is
turned up, you might have to work on the coil of wire on the ferrite rod. The ferrite rod is the long black thing that's between about 50 and 150mm long, located near the tuning capacitor. The coil is usually wound on a light cardboard
sleeve wrapped around the rod. Without disturbing the windings, slide this coil towards one end of the rod. If the sleeve does not move along the rod, gently dislodge the wax that's holding it tight. You should hear an increase in signal strength, or if there is no activity on the band, noise level. Secure the sleeve with either wax, tape or a small dab of glue.
14. Replace back and rotate set for best signal.
All this should only take 15 minutes and requires no soldering or knowledge of electronics. The video demonstration below may help if you get stuck.
Receiving SSB on an AM receiver
If you need to resolve SSB 'duck talk' signals you will need a beat frequency oscillator, which produces a small local signal on either the
main receiver's intermediate frequency or the actual frequency of reception. Either build one or use another old AM radio. For the latter,
position it near the main receiver and tune 1350 - 1400 kHz on the dial. This will place its local oscillator just above 1800 kHz.
If you hear 'duck talk' tune the second receiver until the sound from the modified receiver changes. If the tuning is adjusted very
carefully you will be able to understand the transmission. Morse is similar except the tuning is less critical. Move the BFO receiver
closer or further away from the main receiver for best results with varying signals. A video demonstration of the concept is below.
Buying a radio for 160 metres
Many of the better sets that cover 'shortwave' also cover 160 metres. Look for a radio that offers
'continuous coverage' over the 0.53 to 30 megahertz range. If it has a 'BFO' or beat frequency oscillator,
so much the better as you will be able to hear single sideband (voice) and CW (morse) signals.
Some newer sets offer digital readouts, but may still miss 160 metres. Some older sets with dial
tuning may have a shortwave range that covers 1.6 to 4.0 megahertz. This will allow reception of
160 (and 80) metres without modification, but will need a BFO for SSB.
Building a radio for 160 metres
If you are within 3km of a 160 metre AM operator, and have a good antenna, signals can be heard
on a batteryless crystal set receiver. However amateurs use lower power than most broadcasters,
so a better receiver is almost essential.
A type of radio called a regenerative receiver is excellent for the job and quite simple to build. You could even
make it cover both the AM broadcast band and 160 metres and be able to receive signals from interstate if conditons
are favourable. Here's an example.
Add an up-converter to a 27 MHz CB radio
Just a few parts will allow 160 metre reception. Demonstration and circuit is below:
160 metre propagation: How far can I hear?
During the day 160 metres provides good local coverage out to about 50 km. At night distances possible increase,
with interstate contacts being possible. If conditions are really good, or if you have a good receiver, proper antenna and
location without much interference, you will hear North Americans and New Zealanders at night and Europeans in the early
morning. Around sunrise and sunset are the best times for really long distance reception. Note though that all long-distance
activity is SSB and CW, and AM is more suited to local communication.
Improving 160m reception
If you are within 10 or 20 km of most stations, you probably won't need an external antenna. However a wire or loop will help on weaker signals.
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