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antenna tuner

You do not need to invest huge amount of money to give to your Atlas the antenna tuner it needs  .With junk components gathered in your prefer flea market it will cost you almost nothing to get a tuner being able to make your Atlas210 happy whatever antenna you have .All you need is a coil and 2 variable condensators and 3 aligator clips .This tuner is able to get a low SWR  from 3.5  to 21 mhz  with load ranging from 10 ohm up to 2000 ohm being either capacitive or reactive .With this tuner and a dipole 2x 10 meters connected to a ladder line you will be able to work on all amateur band from 3.5 up to 21 mhz band

The schematic  is shown herewith .The ATLAS is connected to coil  L1 using standard coax cable .The ladder line antenna is connected to L2 .Physical dimensions  are given on the drawing  .None are critical .Depending on the capactiors values you can change the number of turns and/or the diameter of the loop .The loop is made of standard electric wire (2.5 mm2 section)
schamatic of antenna tuner
tuner assembled

If you want to give to this equipment a nice "amateur touch" you can simply glue all components on a plate of wood .This is an easier way than to put it in a metal cabinet which is generally common practice  . As shown you can use BCL capacitors for C1 and C2 .If each have double sections  you can use 1 of the 2 or put the 2 in parallel or the 2 in series .Of course the value of the resulting capacitance is not the same for these different configurations .The maximum power which can be handle by this tuner depend on a large extend of the maximum voltage that the C2 capacitor is able to handle before arcing .Event with  BCL capacitors it is possible to get the full power of ATLAS into the tuner as long as the antenna impedance is not too low (more than 10 ohms)
The adjustement is quite straightforward . With the antenna connected you will have to find the positions of the 3 aligator clips giving the lowest SWR in the coax line between the ATLAS and the tuner ,by  adjusting the 2 variables capacitors .Of course it is a good practice to  start at low power (i.e around 10 watts)  to prevent problem with the PA of the transceiver  .As a rule for the 3.5 mhz band use all  L2 for capacitor  C2 and half of L1  for tapping the TX  .Adjust  C1 and C2 for lowest SWR .If not perfect move first the antenna tab on L1  and/or TX tab on L1 .For the other bands you reduce the number of turns of L2 in the same ratio as the frequency .Initial tuning can be done using a dummy load .It is not necessary that this one is pureley resistive .You can use  for example ligthing bulbs : for example a 100 watts 220 volts can do the job .To have an idea of the real impedance seen by the tuner at the end of the ladder line for the various band you want to operate  is is a good idea to calculate it using various package available like for example MMANA (freeware) .Wiht a little practice it does not take more than 30 seconds to perfectly match the antenna to the ATLAS .

In some case especially when the impedance is low it is better to tune the L2 coil not in parallel as show above but in serie as shown here .serial tuning

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