THE BARLOW WADLEY XCR-30
The Barlow Wadley XCR-30 portable shortwave receiver.
The Barlow Wadley XCR-30 portable shortwave receiver with
serial number 11270. Frequency stability due to the Wadley loop!
This portable shortwave receiver for AM, SSB and CW reception was quite famous in the '70s. When this receiver was designed, there were no DDS and PLL chips available. Therefore, the frequency stability is obtained by the Wadley loop. Many very creative electrical and mechanical solutions can be found in the receiver. The frequency band 0.5 MHz to 30 MHz is covered in 30 bands of 1 MHz. Compared to similar receivers of those days, the frequency stability and reception quality is very good and the analog frequency scale quite accurate (10 kHz). Tuning to an SSB station is not difficult due to the fact that the whole shortwave is split into 30 bands of 1 MHz and the clarifier.
The receiver is portable but quite heavy. However, there is one advantage compared to modern receivers: battery current is only 15 to 25 mA! I used the receiver a lot during holidays and weekend trips but never had to change the batteries because they were empty, only because they were old! Even now, 30 years old, the receiver works good, it never had to be repaired or adjusted. Only the switches have to be cleaned now. And of course, you can see that the receiver is used very much, not only the switches should be cleaned...
This receiver is used very often!
It was worth its price of 160 Euro that I had to pay for this second hand receiver in 1978!
I always took it with me while on holidays when camping, sailing or staying in a hotel. This receiver is used for listening to national broadcasts on the shortwave during holidays abroad, for listening to coastal traffic on 500 kHz (Morse), 2182 kHz (Speech), weather forecasts of coastal stations during sailing, radio amateurs during holidays or at home in the garden, or it is tuned to my favourite AM broadcast station.
Old technique with many complex mechanical components and adjusments.
Many mechanical components had to be used for the realisation of the receiver with Wadley loop. All the tuning is done by variable capacitors. The selective bandpass antenna filter at the input is tuned by permeability tuning, a core moves up and downwards into a coil. Parts of the coil are switched by micro switches. The tuning knob for this bandpass antenna filter does move the core and also activates the micro switches.
Big mechanical dials are used to read the frequency. There are many bandpass filter coils and trimmers that have to be adjusted. It was indeed quite a complex radio with many mechanical parts.
Explanation of the receiver and the Wadley loop.
Variable capacitors for the MHz and kHz tuning, permeability tuning
with micro switches for the bandpass antenna filter (right side).
In principle, it is a receiver from 2 to 3 MHz. The whole band 0 MHz to 31 MHz is converted to this frequency range in 1 MHz steps.
The Variable Frequency Oscillator (VFO) should be tuned close to 45.5, 46.5, 47.5,......73.5, 74.5, 75.5 MHz, depending on which 1 MHz range between 0 MHz and 31 MHz you want to receive. In passive mixer 1, this desired 1 MHz range is converted to the 1st IF of 45 MHz (44.5 - 45.5 MHz). In passive mixer 2, a harmonic from the 1 MHz harmonic generator is also converted with this VFO signal to a 42.5 MHz amplifier. In the passive mixer 3, this 42.5 MHz signal converts the 1st IF downwards to 2 - 3 MHz, the 1 MHz tuning range of the basic receiver.
If the VFO drifts a little in frequency, the 1st IF and the 42.5 MHz signal do also drift with the same value but the difference (the 2 - 3 MHz signal) will not change! So the stability of the 2 - 3 MHz output signal of passive mixer 3 is only dependent on the stability of the 1 MHz crystal oscillator!
Block diagram of the receiver
Click here for the schematic diagram of the receiver
And that was it all. These modifications are not something an unexperienced amateur should do. Therefore, I only give here the diagram of that modifications without a detailed story about how to do it.
- The 5 pF capacitor C1 was replaced by a trimmer so that it can be adjusted to even lower values than 5 pF to prevent overloading the receiver when using my long wire antenna.
- A FET was added to the transistor RF amplifier to increase the Q-factor of the selective antenna filter.
- The gain of the RF amplifier was reduced. The sensitivity was quite high, there was much intermodulation caused by very strong shortwave signals in the evening. The reduction of the RF gain solved these problems, especially when using a wire antenna instead of the telescopic whip antenna.
- A connection for an external ferrite rod antenna for medium wave and long wave reception with active preamplifier was made. The sensitivity is very good with this ferrite rod antenna, much better than with the whip antenna. Long wave reception is also possible with this modification, not with the original receiver. Navtex on 518 kHz and longwave beacons between 260 and 400 kHz that are (were) used by ships and aircrafts can also be received.
The circuit diagram of the modifications.
RF gain can be increased by decreasing the 120 ohm.
The connector for the ferrite rod antenna
for medium and longwave reception.
For a portable receiver, the performance is good. You can receive 95% of wat you want to hear. And it is certainly NOT a battery eater, so a perfect receiver for portable use! Even when compared to modern portable receivers, it is one of the best there is, although the technique is old.
A problem is however that the 1st IF is 1 MHz wide, all kinds of strong signals are present and mixed in the 1st IF and the 1st and 2nd mixer. Therefore, dynamic range and intermodulation are not as good as that of a modern base station receiver with a narrow filter after the 1st mixer. However, that is not so important for a portable receiver with a telescopic antenna.
Stability is good enough for SSB but not as good as that of a receiver with DDS and PLL technology. That is due to the fact that the VFO and BFO of the 2 - 3 MHz basic receiver are free running L/C oscillators. The analog frequency scale is not as accurate as a digital display.
But the receiver is designed for portable use and should not be compared with a base station receiver for use in the shack. I was always very satified about the performance. With the addition of the external ferrite antenna, it is also an excellent receiver for the medium wave, even indoors!
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