RAN Technology

JSB-20 Synthesizer demo


Ham Radio Information 0 Comments 12/12/2020

Tuning and USB/LSB selection

Posted By: Robert Nickels (ranickels)
Post Date: 12/12/2020

This is a short video that shows my external Arduino-controlled frequency synthesizer that is used to make the JRC JSB-20 frequency agile.    Tuning is implemented  by means of up/down switches much like the decade switches used on many military packset radios, although knob-tuning can be done just as easily.    I have not yet printed a graphic overlay so the bare capacitive touchswitches are still visible, but any desired graphics can be added to customize the keypad.   As the photos show, the LCD display is backlit for easy viewing.

The radio can be configured for four channels between 3 and 9 MHz, but with the synthesizer substituting for crystals, I just aligned the first three channels for the middle of the 80, 60, and 40 meter bands.   Thus the channel switch now works like a bandswitch, and tuning within each band is done from the keypad.  

JRC sold this as a USB-only radio since outside the ham world, all mil and commericial SSB users operated on USB only regardless of frequency.  However the synthesizer make it possible to have selectable USB/LSB which is obviously a requirement for normal ham use.   However I do use USB on nets like the MMRCG Saturday morning net on 7296 which is conducted in USB mode because of this restriction in some mil/commercial radios.

The internal construction quality is very high as can be seen, yet the two main boards and front panel can be separated easily for repairs or re-crystalling.   An innovative feature is the use of varactor tuning diodes for each tuned circuit so alignment is accomplished by adjusting a single trimpot that applies the needed voltage to peak the  signal for each frequency.   These tuned circuits are broad enough that it's possible to QSY within a band but also makes the JSB-20 receiver more susceptible to overload and intermod when many strong signals are present.  I've found this to be an issue on 40 meters at night when the 41 meter SWBC stations are blasting in, but it would be much less of a problem using a whip or less efficient antenna in the original application.    Waiting for different propagation or trying an alternate frequency would have been the protocol in the field.

Alan Barrow KM4BA has been responsible for creating the JSB-20 group and for making the complete package of technical information possible, without which I would not have been able to do the modifications and enjoy using my JSB-20, so a big thank you, Alan!

73, Bob W9RAN


  

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