I would like to construct base-loaded coil antennas for both an Sstran300 and a Talking house transmitter.
Anyway, suppose I build a prototype antenna and want to match it to an antenna......
1) Is there any way to match the antenna and measure SWR without expensive test equipment? (Even the HAM stuff seems to have trouble at 100 MW.)
2) Regarding the SStran, I still don't have a manual, but... Would I be able to match a base-loaded antenna design (like the one on the sstran website) using a procedure described in the manual? I believe I read that there is a trimmer pot that can be adjusted and the voltage at a test point can be maximized using a multimeter??. Also, some coils that need to be switched out using a dip switch.
Thanks, Perry
1) This doesn't measure SWR but it does indicate antenna system resonance: http://www.part15.us/node/3829 . This may not work with the AMT-3000 system because it is tuned slightly off resonance.
2) Should work. There is also a recommended parts change for use with a base coil loaded antenna. Achieving the best performance is a matter of adjusting the coil taps, antenna length, and trimmer capacitor. You should get a manual which describes the process.
Neil
There is some good argument for using a center loaded antenna. Also, contact SSTRAN directly for advice on what to switch out. If I remember correctly, you have to change the value of one or two capacitors in the output circuit. Very easy to do.
As said by WDCX the AMT3000 mod is easy to make, and is detailed not in the manual, but in a white paper on loading coil design offered at sstran.com.
I built a loading coil for mine on a triangular shaped form, but of course a circular form is the most normal configuration.
Mine is base loaded and does very well, but now I'm curious about center loading and might give it a try.
We found the sstran 3000 manual!! Moved the frequency up to 1590, flipped in the 4 position DIP to select the proper coils and adjusted the trimmer CAP to peak the voltage between TP1 &TP2. A greatly improved range now on just the wire antenna. About 1/4 mile listenable range and another tenth of a mile sporadically!
Yes, I found the white paper link on the Stran website. Looks like that will be the next project.
To PerryNH and others...
This wonderful contribution was made a few months back by PhilB, the inventor of the AMT3000 & 5000 transmitter.
http://www.part15.us/node/2728
Electrically,
NO loading is best.
Followed by Top loading, center loading, base loading.
now, mechanically... It is the opposite!
Since you are planning a mobile antenna, mechanics are, by far, the important issue here!
From a practical standpoint, start with a base design!
My AMT3000 SStran Manual says that "Jumper S7 must be installed to short across resistor R14 in the meter driving circuit when you use the external base-loaded vertical described at (sstran website)."