I found this rather interesting website with online calculator. Certainly there to make life easier for the end fed antenna enthusiast. It also follows the same lines of Pierre ZS6A’s spreadsheet mentioned before in other topics and should be followed.
I have chosen these three bands typically because it’s the bands my HB1A can transmit on. My HB1A is constantly a work in progress since I had to repair it myself and see chance in modifying it. See https://zs6bne.wordpress.com/2017/05/19/youkits-hb1a-replacing-the-lcd-module/
It makes sense to build a 3 band end fed tuner into the rig as that is typically the antenna I would use with it! So …… the next project is ….. and now to figure out the best way to do that with minimum modification.
Note the Q Value stays constant …..The Q (bandwidth) of a filter is fixed for an L matching network, because it is set by the ratio of the source and load resistance which are typically fixed values. For a variable Q use a Pi or T matching network.
Some examples executed there:
40m – 7.1 MHz
From Pierre’s spreadsheet
30m – 10.125 MHz
20m – 14.175 MHz
That basically comes down to this table of values ……
Over complicated inductance switching maybe ?
Or simply ……….. a 1:64 impedance transformer and parallel tuned circuit on the secondary.
A 10 uH inductor wound on a T80-2 toroid will need 43 turns (103 cm of wire) and the following capacitance values / band.
40m – 50 pF
30m – 25 pF
20m – 13 pF
Or using the values from the above link :
A 2.8 uH inductor wound on a T50-2 toroid will need 24 turns (60 cm of wire) and the following capacitance values / band.
40m – 178 pF
30m – 78 pF
20m – 40 pF
So, which is best ???
As calculated using Pierre’s spreadsheet, I will make the radiator like one leg of a linked dipole.
The lengths of the radiators are:
7.1 MHz – 20.6 meters
10.125 MHz – 14.4 meters
14.175 MHz – 10.3 meters
I was thinking of using the hole usually used for the BNC female adapter as a place to mount a varicon capacitor! Hopefully it will fit there!!!
The T80-2 could be fixed to the back cover (Usually where one would foolishly have penlight battery holders) and also holes drilled and fitted with female banana plug sockets for the radiator (end fed antenna) and a short counterpoise wire that can lay on the ground.
The plan is coming together …… I think!
73 de Eddie ZS6BNE