“The converter to be described was designed for working into the Type BC-453 aircraft receiver, commonly known as the “Q5-er.” The combination of converter and receiver gives a high-stability, high-performance, accurately- calibrated c.w. or ‘phone receiving system of extremely small dimensions. As shown, it will tune over the 80- and 40-meter bands, and methods for extending the range to the higher frequencies will be suggested.
The BC-453 tunes from 0.19 to 0.55 Mc. It has high-order selectivity, obtained in a two-stage 85kc. i.f. amplifier. Its gain is sufficient to give adequate volume from the one-tube converter to be described.
The converter is crystal-controlled, and all tuning is done with the BC-453. If the oscillator portion of the converter is set at 6.75 or 7.55 Mc., tuning the Q5-er from 0.25 to 0.55 Mc. will cover the 40-meter band. Since the SO-meter band is 500 kc wide, it is necessary to furnish two oscillator frequencies for this band. To cover 3.5 to 3.85 Mc., the oscillator frequency is 4.05 Mc., and to cover 3.65 to 4.0 Mc. requires an oscillator frequency of 4..55 Mc. This permits covering either the ‘phone portion or the mainly-used c.w. portion of the 80-meter band with one oscillator frequency, while maintaining a relatively high i.f. to minimize image response. No r.f. stage is used in._ the converter because images are not troublesome and atmospheric noise is large com- pared with mixer noise.
The circuit diagram of the converter is shown in Fig. 1. An ordinary 2.5mh r.f. choke is used as a plate load for the converter, so the output section needs no tuning. However, a variable condenser is used in the input circuit so that various antennas can be compensated for and Rotations can be peaked at various parts of the band. This tuning minimizes image response, but this control need be touched only during wide tuning excursions.
If any crystal will not oscillate in the converter, the values of C3 and C5 can be varied to change the feed-back. The oscillator portion of the 6BE6 does not have a great deal of gain, and these condensers are needed to obtain sufficient feed-back for reliable operation. In addition, Ca insures that plate and screen loads are not tuned to the same frequency. Calibration accuracy is potentially great with this system, because the aircraft receiver is accurate over its frequency range. The dial divisions represent 10kc. intervals, and it should be easy to log stations to within the nearest kilocycle. The BC-453 receiver can be realigned slightly to compensate for any one crystal being off a few kilocycles, but in the long run it probably would be more satisfactory to use the correct crystals throughout.”
My Converter is based on a circuit that was build and demonstrated by WU2D. M. Murphy. It is working well on 40m band. I am awaiting the arrival of a crystal that will make the 80m band available to me.
This is my first completed project. It makes use of some parts that were given to me by a former op. This chassis started life as a 40m QRP transmitter, and I repurposed it into the converter. I made use of was many original parts as possible.
I would like to build the circuit featured in this post, sometime.
Here is the receiver paired up with a Heathkit DX-20 transmitter. I need to find a more suitable location for the transmitter.
Well the converter needed some work. It would not resonate on the 4040kc crystal. So with the help of the online coil calculator from Professor Coyle and N2EY in Wayne PA, I found I needed to reduce the main coil to just 15 turns instead of the 22 that were already on the coil form. Now 80m tunes in as expected.
Many thanks to N2EY and WU2D for their help in getting this converter working and understanding how the circuit functions.
A little history of the hardware. The chassis for the converter including the coil was from an SK ham who had started to build a 40m QRP transmitter. I did not need another transmitter, so the chassis and as many parts as possible were repurposed into the converter.
The Power supply in the middle was build and given to me by W4UFP, a person I have come to know through the enjoyment of radio.