[Antennas] ATAS-25

Mon Dec 26 17:52:17 EST 2005

Hi Murray:
The ATAS-25 is not what I would call a simultaneous-resonant antenna on all 
HF bands. In other words, this antenna is really intended for temporary 
portable use and must be retuned each time you change bands. As such, it is not the 
best antenna for SWLing purposes.
This antenna is tricky to use but I would above all, suggest that you read 
the manual. The manual only has you place all the radiating elements (3) on the 
antenna when you are either on 40M, 15M, and perhaps on the CW portion of the 
20M band. As you go up in frequency, you drop off upper radiating element 
sections per the manual instructions, leaving on the bottom coil assembly. Until 
you tune the bottom coil assembly, the radio/antenna combo will be 
dead............noise wise.
In order to tune this antenna, put out all the HF radials as this will serve 
to further reduce the SWR and thus enhance the antenna performance. Now, for 
sake of conversation, lets limit the tuning to one band....40M. Simply place 
three of the radiating elements onto the top of bottom coil assembly. Now, 
ensuring the coax from the antenna is hooked up to the radio, turn the radio onto 
the appropriate band and turn up the volume. Now, within earshot of the radio, 
raise/lower the bottom coil assembly until you hear the band noise peak on 
the radio. (If you don't hear a peak in the band noise, remove one of the 
radiating elements and repeat.) At this point, you are what I would say rough-tuned 
which should prove adequate for SWLing purposes. 
Now, if you were licensed to do so, you could go back to the radio and 
"squirt" a little 7 MHz RF into the antenna and check the SWR. If the SWR was still 
a little high, you would need to go back to the antenna and slightly twist 
the coil assembly CW or CCW, each time going back to the radio to check the 
SWR.
Yes, you will get a workout as it takes several trips back and forth between 
the radio and the antenna. Here is the big gotcha': The tuning of the antenna 
will be affected by your body so be patient.
Need to change bands?............The whole process starts over again!
Is there any easier way to tune this beast? Yes, through the use of one of 
the popular antenna analyzers manufactured by companies like Autek and MFJ.
Murray, the great thing about this antenna is that tuning it will give you 
plenty of exercise to shed those extra pounds from those extra pieces of pie you 
consumed over the holidays!
GL
Val Erwin
W5PUT