Geoff's Fascinating Loose Coupler Radios
Art and Technical Performance Combined!
Imagine a time in a bygone age when our lives were uncluttered with technology how magical it must have been to hear the first Broadcast Radio Stations on nothing much more than a copper coil of wire and a crystal mineral no battery no power supplies.
Something that Grandpa made up one Sunday afternoon in his backyard workshop. How was it possible to pull those voices and music from out of thin air. Imagine all the family gathered round in a candle lit room and taking turns to listen to their favorite Radio program on those old Bakelite headphones and the Loose coupler Radio. Hearken back to those times and remember and feel the excitement the whole world was now just at our fingertips.
See my handmade crystal radios.
Click on the pictures for a larger view.
Loose Coupler For Long and Medium Wave.
This is a dual slider main coil plus retractable detector winding.
The detector winding is switchable. The main winding has slide
and stepped positions so you can return to a specific point on the coil.
The main coil is 4 inches diameter and 7 inches long the retractable
coil is 3 inches diameter and 6 inches long. The overall set is 13
inches long. I wound the large coil on a modified woodworking lathe
and the smaller coil was wound on my AVO machine.
The retractable coil slides along twin brass rails and is very smooth
and makes good contact. The spring loaded switch makes a very good
contact on the switch studs. There is an internal spring which pulls
the contacts together. There are six taps on the coils.
I based the design on a 1920's Murdock set from USA.
It was a satisfying craft project but for the amount of work (50 hours).
It looks better than it actually works. This particular type of set was
dropped by manufacturers in the 1920's for exactly the same reasons.
Other simpler sets work possibly better but from a visual point of
view these sets are stunning and highly collectable items.
Please click on the photographs for a larger picture of this beautiful wireless receiver.
Loose Coupler For Long and Medium Wave.
I had to build another of these sets to experiment with as the last one was sold rather quickly.
This time I decided to build it on a longer base so I could add a diode detector as well as the Galena detector plus a simple switch to change from one detector to the other.
In the days when these sets were firstly made there were no Germanium diodes so I was keen to see how well it worked on the diode. Have I found a long lost secret here as It worked fantastic and was surprisingly loud .I would go as far to say it is the loudest set I have ever made with an enamel wire coil. Radio 4 on Long wave was very strong indeed but is 500KWatts! Almost too loud for easy listening with my Nathaniel Baldwin Armature type phones it was necessary to decouple it a bit to reduce the volume.
I could not find much information on the internet about this type of set before I made one but there were lots of photos of sets from the 1920's no technical information on how well they worked. I guess now it was a well kept secret as they are really superb and worth the effort to wind the big coils and the coupling mechanism.
I had no winding instructions from any technical source so looking at the photos of the Murdock Loose coupler design which was one that I particularly liked esthetically I made a guess at the inductances.
The main coil was 4 inch diameter x 6 inch long the inductance was1600uH or 175 turns approximately of .8mm wire and the secondary coil 3 inch diameter and 5 inch long and was wound using .5 mm wire inductance 1800 uH. The secondary coil was wound with taps every inch spacing giving me 6 tapped coils altogether.
Tuning the set was something completely different to any other set I have made. It appears to tune in three different ways. Firstly by selecting a tapping on the centre switch and then by moving secondary coil into the main coil it would tune into a station and reach a peak volume.
Then if the slider control on the side was set to fully left hand position and the top slider was set to the fully right hand position I could tune long wave and Radio 4 on 198 KHz came in loud and clear. I don't see any way to calibrate this type of radio with a tuning scale but you soon get used to the various settings to find a station.
To tune medium wave I moved the lower slider to the right and the selector switch to the anticlockwise position by a couple of positions. Many stations on medium wave could be heard and the selectivity was not at all bad considering there is no capacitor to fine tune the set. It will need a lot more experimenting to fully understand the relationship between sliders coupling and switch, however hats off to the original inventors of this type of radio. They are a very satisfying project to make and to tune round the Airwaves.They look very esthetically pleasing to my eye.
A proper Radio ! I must build a MK3.
Diode Detector and Selector Switch
Main Selector Switch (Coil taps)