?C.F.Simmons from Max vk2tti.
It is possable to use different size loops with one capacitive tune/match sysrem. This idea is used in the MFJ936B loop tuner. I clean the contact areas with a brass brush before each use. Soldering would be better but you lose adaptability. For transmitting purposes the loop needs to be of an optimum length for each amateur band such that the capacitor vanes are in half mesh. For receive purposes great accuracy in tuning cannot be achieved as the signal waxes and wanes making it difficult to tune with precision. This has been my experience. Regards to all vk2tti.
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Mon, 2 Dec 2013 10:27:20 +0300
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[loopantennas] same capacitor different loops
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If you could swap the size of the actual loop and use the SAME capacitor would this be possible. In other words if you were to build a loop better suited for say 14 mhz - 228/29 mhz and a separate loop with dimensions better suited for say 7 mhz - 14 mhz, could you use a capacitor with enough, correct minimum and maximum capacitance to work on both antennas. For now lets just say QRP power levels only. I fully understand the losses that occur with the connections? and the other problems associated with? doing the, just trying to see if there is a capacitor range that is possible for both using just one capacitor. The M??-Loop uses the exact size loop for both antennas they sell, one includes 40 meters (Larger capacitor-Higher capacitance) and a smaller one for covering 10 meters -20, losing 30 and 40 meters (Has a lower range of capacitance). This question cam to mind thinking if everything is not permanent, all connections soldered (Not removable) this would be best! But..... for portable use, you will have to disconnect something, and if you could design a put together frame, with say ideal different size loops using the same capacitor this would be good. One bag of frame items, two loops (Made of something- to be determined) and one frame mounted capacitor that works for both. Looking at the two different capacitors used by M?? loop, if you had a capacitor that would go between 10-12pf (low) and 136-140pf (high) this could maybe cover both. This seems would be something that could be done because as you have a length of conductive material closer to the ideal band you are trying to get the loop to work, the capacitance is more predictable. Say different size loops, swappable and attachable to the same lugs,screws, mounting bolts, SO-239 connectors, whatever you decide to use for connection. If you look at every other "Portable Loop" there is, the connection is always less efficient and a permanent soldered connection. keeping this in mind, can we use the same capacitor, with different size loops to achieve better overall efficiency due to the actual size of the loop being optimized for the attended band(s).
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