An important point worth mentioning here is that the life of gas discharge tubes is reduced every time they conduct. Exactly how much depends on the arc current, which is explained in the Bournes GDT data sheets, but their life can be significantly extended by the following simple and inexpensive modification.
After I read that data sheet, I started paralleling 33k Ohmite OX resistors across the 90v GDTs (between each Beverage wire and ground) to prolong their life. Those resistors provide a DC path to ground, which constantly drains static charges to ground. This eliminates many small discharges through them from the inevitable static charges that would otherwise build up, thus prolonging their useful life. These Beverages have a surge impedance of about 450 ohms. Therefore, 33k (some use 47k, 10 times the surge Z) resistors will have a minimal effect on received signal strength, RDF, or the required matching transformer impedance ratio. For a higher impedance antenna, the drain resistors should have a correspondingly higher value (and perhaps a TVS diode should also be in parallel with the GDTs and resistors?). Some well-meaning hams have recommended much higher value resistors as a static drain, even at a transmitting antenna feedpoint where GDTs are seldom practical. However, if the resistance value chosen is as low as practical, then the GDT's life will be maximized. 73, Mike W0BTU _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
