Monday, 9 March 2020

Ham Radio EFHW Grounding Compared, End Fed Half Wave Matching system

Ham Radio EFHW Grounding Compared, End Fed Half Wave Matching system


                 


Ham Radio EFHW Grounding Compared, End Fed Half Wave Matching system.  I am indebted to Steve Ellington for uploading this video showing a comparison to different types of grounding the popular EFHW aerial. Steve has another video that shows the construction of a matching unit using ferrite rings to construct a transformer, the end of an aerial such as the end fed is where the voltage along the wire is at its maximum.

We need to transform this high voltage and impedance down to the output of the transceiver which nowadays is an unbalanced 50-ohm output. Over many years I have built many matching transformers, the popular one seems to be a 49:1 ration transformer.

My experience has shown that the impedance on an EFHW can range from 2500-3000 to 5000 ohms, working on the 49:1 ratio we have a system that will transform 2500 ohms down to 50, we do this by calculating the square root of 49 which is 7, dividing 2500 by 50 is 50 an approximate number to 49.

T make a transformer to match this system I used one ferrite core or ring a T240-43 ferrite, with fourteen turns of copper wire as the secondary winding and two turns as the primary winding to give the ration mentioned above, this arrangement worked well with 100 watts.

My end fed half wave transformer was tested with and without a counterpoise, I observed little difference in the SWR reading, however, Steve is an American radio ham and probably ran more power into his aerial hence the three stacked ferrite rings.

One of the two primary wires is used for connection to a counterpoise and consists of 0.05 of a wavelength at the frequency of operation, in my case 20 meters or 14 Mhz the counterpoise works out to be 1 meter long.

Some experimentation is required with this matching transformer, adding more turns to the secondary may be required, for example, if our aerial is 5000 ohms we would need twenty turns on the secondary side.

Thank you for reading  73 de John G4YDM

Ham Radio EFHW Grounding Compared, End Fed Half Wave Matching system







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