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“Ohm’s  Law”,  named  for  Georg  Simon  Ohm  of  Germany,  who  first  discovered  the  principle  in 
1826. In RF circuits,  an analogous  but  more complicated  relationship  exists. 

RF  circuits  also  resist  the  flow  of  electricity.  However,  the  presence  of  capacitive  and 

inductive  elements  causes  the  voltage  to  lead  or  lag  the  current,  respectively.  In  RF  circuits,  this 
resistance  to  the  flow  of  electricity  is  called  “impedance”,  and  can  include  all  three  elements: 
resistive,  capacitive,  and inductive.   

The  output  circuit  of  a  transmitter  consists  of  inductors  and  capacitors,  usually  in  a 

series/parallel  configuration  called  a  “pi  network”.  The  transmission  line  can  be  thought  of  as  a 
long  string  of  capacitors  and  inductors  in  series/parallel,  and  the  antenna  is  a  kind  of  resonant 
circuit.  At  any  given  RF  frequency,  each  of  these  can  exhibit  resistance,  and  impedance  in  the 
form  of capacitive  or inductive  “reactance”. 

Transmitters, transmission lines, antennas, and impedance 

The  output  circuit  of  a  transmitter,  the  transmission  line,  and  the  antenna,  all  have  a 

characteristic  impedance.  For  reasons  beyond  the  scope  of  this  document,  the  standard 
impedance  is  nominally  50  ohms  resistive,  with  zero  capacitive  and  zero  inductive  components. 
When  all  three  parts  of  the  system  have  the  same  impedance,  the  system  is  said  to  be  “matched”, 

and  maximum  transfer  of  power  from  the  transmitter  to  the  antenna  occurs.  While  the  transmitter 
output  circuit  and  transmission  line  are  of  fixed,  carefully  designed  impedance,  the  antenna 
presents  50-ohm,  non-reactive  load  only  at  its  natural  resonant  frequencies.  At  other  frequencies, 
it  will  exhibit  capacitive  or  inductive  reactance,  causing  it  to  have  an  impedance  other  than  50 
ohms.   

When  the  impedance  of  the  antenna  is  different  from  that  of  the  transmitter  and  transmission 

line,  a  “mismatch”  is  said  to  exist.  In  this  case,  some  of  the  RF  energy  from  the  transmitter  is 
reflected  from  the  antenna  back  down  the  transmission  line  and  into  the  transmitter.  If  this 
reflected  energy  is strong  enough,  it  can damage  the  transmitter’s  output  circuits.   

The  ratio  of  transmitted  to  reflected  energy  is  called  the  “standing  wave  ratio”,  or  SWR.  An 

SWR  of  1  (sometimes  written  1:1)  indicates  a  perfect  match.  As  more  energy  is  reflected,  the 
SWR  increases  to  2,  3,  or  higher.  As  a  general  rule,  modern  solid  state  transmitters  must  operate 
with  an  SWR  of  2  or  less.  Tube  exciters  are  somewhat  more  tolerant  of  high  SWR.  If  a  50  ohm 
antenna  is  resonant  at  the  operating  frequency,  it  will  show  an  SWR  close  to  1.  However,  this  is 

Summary of Contents for AT-100ProII

Page 1: ...ONS MANUAL MANUAL REV A PAGE 1 LDG AT 100ProII 100W Automatic Antenna Tuner LDG Electronics 1445 Parran Road St Leonard MD 20685 2903 USA Phone 410 586 2177 Fax 410 586 8475 ldg ldgelectronics com www...

Page 2: ...ndication 15 Advanced Operation 17 Manual Inductor Capacitor Adjustments 17 High Low Impedance Relay Adjustment 17 Manual Memory Store 17 Status Check 17 Application Notes 18 Mobile Operation 18 Conse...

Page 3: ...king it suitable for battery powered operation JUMPSTART OR REAL HAMS DON T READ MANUALS Ok but at least read this one section before operating the AT 100ProII Connect a 50 ohm coax jumper cable from...

Page 4: ...5 5 x 2 0 Weight 1 5 pounds AN IMPORTANT WORD ABOUT POWER LEVELS The AT 100ProII is rated at 125 watts maximum power input at most Many ham transmitters and transceivers and virtually all amplifiers...

Page 5: ...ctance Tune Initiates memory or full tuning cycle Momentary push places tuner in bypass PWR Meter Bargraph display indicates forward power in 0 12 5 and 0 125 watt ranges SWR Meter Bargraph display in...

Page 6: ...to this SO 239 connector Gnd wing nut Connect to the antenna system ground Tx Connect a 50 ohm jumper coax from this jack to the ANT jack on the rear of the transceiver Radio Connect the optional radi...

Page 7: ...3 or AH 4 external tuner connect the 4 pin Molex connector of the optional ICOM interface cable to the radio s Tuner port Then connect the 1 8 stereo plug on the other end of the ICOM interface cable...

Page 8: ...PAGE 8...

Page 9: ...ton is held for one half to 2 5 seconds and then released Long Press The button is held for more than 2 5 seconds and then is released FUNC Button The FUNC button is pressed first and then the button...

Page 10: ...s suitable for 100 duty cycle modes such as FM RTTY or PSK Peak mode is more useful on modes with varying duty cycle such as SSB or AM The factory default is average mode To toggle between power displ...

Page 11: ...evel The default setting is fully automatic tuning mode To toggle between semi and fully automatic modes press Func C Dn The LED display will show one of the two patterns to indicate which mode has be...

Page 12: ...d when the new antenna is selected Transmitting and Receiving During receive operation only the antenna indicator LED is normally lit on the AT 100ProII During transmit the forward RF power level is d...

Page 13: ...uning sequence where the AT 100ProII rapidly tries varying combinations of inductance and capacitance values and then zeroes in on the best match possible When the tuning cycle is complete if an accep...

Page 14: ...optional radio interface cables the radio will automatically reduce power switch to CW mode and begin transmitting while the full tuning cycle is in progress If not key the radio Talk into the mic on...

Page 15: ...the transmitter was not keyed up ERR_LOST_RF RF power disappeared before the tuning cycle completed You must continue to key the radio until the tuning cycle completes ERR_NO_FREQ Unable to determine...

Page 16: ...dditionally if the forward power exceeds the maximum value selected for the meter scale the PWR LEDs will blink an over range condition The four right most LEDs of the PWR bargraph will cycle during o...

Page 17: ...ement multiple times or simply hold the button and the button will auto repeat You may also transmit while incrementing or decrementing so that the SWR value is displayed but the capacitor and inducto...

Page 18: ...Operation The AT 100ProII is perfectly suited to mobile operation It can be installed under the dashboard along with the transceiver or mounted remotely The only requirements are that the tuner remai...

Page 19: ...This is normal and is noticeable the most when using CW in full break in with Peak mode selected In practice this should not be much of a problem as Peak mode is not very useful when using CW MARS CAP...

Page 20: ...sistive with zero capacitive and zero inductive components When all three parts of the system have the same impedance the system is said to be matched and maximum transfer of power from the transmitte...

Page 21: ...minimum SWR is reached The LDG Electronics AT 100ProII automates this process No tuner will fix a bad antenna If the antenna is far from resonance the inefficiencies inherent in such operation are ine...

Page 22: ...ing Diodes rectify the sample and provide a DC voltage proportional to RF power These two voltages are read by the ADCs in the microprocessor and are used to compute SWR in real time Although the micr...

Page 23: ...gle Antenna Selection Toggle High Low Impedance Display High Low Impedance C Up Increase Capacitance Toggle Peak Average Power Display PWR Meter Mode C Dn Decrease Capacitance Toggle Auto Semi Mode Di...

Page 24: ...des links to product manuals just in case you lose this one When you are thinking about the purchase of other LDG products our website also has complete product specifications and photographs you can...

Page 25: ...ng number or a delivery verification receipt This way you know the product arrived safely at LDG Be sure to give us your email address so our shipper can alert you online when your product is en route...

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