RF cables longer than 10 ft. can be problematic in the HOTSHOT and EASYHeat power supply. Both series supplies use a very flexible RF cable to drive a heatstation.
The heatstation is comprised of an impedance matching transformer and a capacitor that series resonates with the coil/part-to-be-heated combination. This architecture limits the high currents generated in the coil to be circulating only a short distance (just at the heatstation) –allowing the use of an extremely flexible cable.
The problem with making the RF cable longer is that every foot adds undesired capacitance to the system. Eventually, that undesired capacitance overshadows the sensed resonant capacitor in the heatstation and could prevent the system from properly tuning.
We know in all cases that 10 ft of RF cable will not interfere with the supply’s ability to tune. Longer cables could become problematic and the actual tolerable distance has to do with the required tap on the impedance matching transformer, frequency of resonance, the value of the series resonant capacitor and the Q of the coil – which has to do with its design and the material to be heated (as well as the coupling efficiency). Because so many factors play a part in determining the maximum cable length, longer cable lengths need to be determined empirically. Empirical methods require that the cable be fabricated to length (+ a couple of feet for margin) and using engineering specific equipment, proven to be compatible.
