Re: Topband: Looking to improve TX antenna Efficiency
Steve, I have an inverted L with 32 feet vertical and then 96 feet horizontal leg. The horizontal leg runs southeast and slopes from 32 down to 10 feet at the last 15 feet of its run. The antenna is resonant with SWR of 1.3 at 1.810. It is fed directly with 50 ohm coax. No chokes, coils or tuning of any sort. I have 5 random length radials made of 14 gauge solid wire. Due to property constraints none of the radials run in a westerly direction. This fall I improved the ground system by adding two more 8 foot ground rods spaced about 19 feet. Those ground rods are all interconnected. I also raised the horizontal leg up as far in a tree as I could. When I raised the horizontal leg the SWR dropped considerably. The antenna plays better now. It seems that the improved ground system helped. I will continue to make ground improvements as this seems to help the most. I cant raise the antenna any higher. Perhaps you can also benefit by improving your ground system? 73, Joe KB3KJS On Tue, 2012-11-20 at 00:23 -0500, Steven Raas wrote: Last 'Season' was my 1st real dive into 160m. Running a 'InvL' ( which I will describe lower in detail ) and 100w, I managed to pull 19 DXCC and 48 states cfmd. I am in looking into ways to improve my TX antenna efficiency, for this season w/o getting to crazy . (rx antennas are in the works and a different topic ) Current TX antenna is as follows: (Tuned in shack / not self reasonant ) Main Element: 32 feet vertical - 90 deg bend ( the 'L' ) which runs 43' horzontally pointing north. Then, another 90 deg bend, and ascending 26' in length ( from 30' up to about 11' above ground running from west to east. ), then..you guessed it.. another 90 deg bend that now runs to the south flat top for 27' ( @ 11' up ) Ground radials qty 24. Min length 22' - max length 62' ( from az 330 deg - 70 deg with the longer radials pointed from 35-60 deg az) The FCP idea is not practicle for me @ this point in time. My Thought.. add a Coil @ the 30' point of the main vertical run made from perhaps 1/8th inch copper tubing ( refrigerant line ) in a fairly large diamater ( 16-20 ), perhaps 14-20 turns even spaced, using perhaps drilled lexan as spacers.. Try extending the vertical run another 8-10' or so.. and then the rest of the antenna as is. Going above 40' vertical is not an option @ this point in time either. ( yes i know the more vertical the better its just a no-can-do for now) At the moment the antenna's best 'swr' is at roughtly 1818 khz @ 2:1 there is no resonant point that I can find within the 160m band. ( no antenna anyalizer either - Mabey santa will provide ) My best guess is that in its current configuration... the antenna is probabally in the 8-12 ohm area.. I have nothing solid to back that up however. At the feed point I have a coaxial choke, 21 turns on a 8 form, the cable is similar to RG213 , with the exception the center conductor is solid. ( its actually 50 ohm quad shielded cable i got form a place I used to work, HP node cluster inter connect cable. .405 blue in color, i cant remember the vf on it but i did spec it out a while back, and its ok for HF use. ) Or, tuning the antenna @ the base with a variable cap. of sufficent size, or perhaps even both? I know there is NO magic that can come..im just trying to improve on what I have and can do @ this point in time. Suggestions, thoughts, flames and raised brows are all welcome. Steve Raas N2JDQ ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: Looking to improve TX antenna Efficiency
We need to put gorilla detectors in SWR meters. Loss in the ground counterpole will be the thousand pound gorilla in the room. Heavily bent antennas as you describe lower the radiation resistance significantly, which makes the resistance of the counterpole even more critical than for a pure 125 foot vertical. Doing stuff in the air with the wire is unlikely to make significant improvements. You will have to deal with the gorilla somehow. I have had people describe a system with family resemblance to yours tell me that the feed Z was 45 to 50 ohms. With an effective radial system, you should be having to match some thing like 15-20 ohms, perhaps less, and it should be fairly narrow. You should need one of those low Z ununs to feed a low, bent wire, unless you've gone long on the wire to raise Z and be content with a lot of NVIS. A friend of mine with a fan vertical, kept adding 125 foot radials made from insulated stranded #18 (he had an inexhaustible supply) on the ground until he quit lowering Z at NINETY of them. At that point it was a 17 ohm feed with a series coil made from 1/4 inch copper tubing. He had to use a unun to step it up to 50 ohms for the trek to the shack. It worked very well. Top ten USA finishes in 160 meter contests. With that much current at the ground, getting dense and uniform all around is worth a lot of radiated energy. Irregular, miscellaneous short radials in/on the ground are just about always serious losers. With a 160 antenna system, the FIRST thing you plan is where and how to deal with radials or counterpoise correctly, which could be quite the difficult exercise, and ONLY THEN start worrying about the wire. The payoff for care to that is huge. 73, Guy. On Tue, Nov 20, 2012 at 12:23 AM, Steven Raas sjr...@gmail.com wrote: Last 'Season' was my 1st real dive into 160m. Running a 'InvL' ( which I will describe lower in detail ) and 100w, I managed to pull 19 DXCC and 48 states cfmd. I am in looking into ways to improve my TX antenna efficiency, for this season w/o getting to crazy . (rx antennas are in the works and a different topic ) Current TX antenna is as follows: (Tuned in shack / not self reasonant ) Main Element: 32 feet vertical - 90 deg bend ( the 'L' ) which runs 43' horzontally pointing north. Then, another 90 deg bend, and ascending 26' in length ( from 30' up to about 11' above ground running from west to east. ), then..you guessed it.. another 90 deg bend that now runs to the south flat top for 27' ( @ 11' up ) Ground radials qty 24. Min length 22' - max length 62' ( from az 330 deg - 70 deg with the longer radials pointed from 35-60 deg az) The FCP idea is not practicle for me @ this point in time. My Thought.. add a Coil @ the 30' point of the main vertical run made from perhaps 1/8th inch copper tubing ( refrigerant line ) in a fairly large diamater ( 16-20 ), perhaps 14-20 turns even spaced, using perhaps drilled lexan as spacers.. Try extending the vertical run another 8-10' or so.. and then the rest of the antenna as is. Going above 40' vertical is not an option @ this point in time either. ( yes i know the more vertical the better its just a no-can-do for now) At the moment the antenna's best 'swr' is at roughtly 1818 khz @ 2:1 there is no resonant point that I can find within the 160m band. ( no antenna anyalizer either - Mabey santa will provide ) My best guess is that in its current configuration... the antenna is probabally in the 8-12 ohm area.. I have nothing solid to back that up however. At the feed point I have a coaxial choke, 21 turns on a 8 form, the cable is similar to RG213 , with the exception the center conductor is solid. ( its actually 50 ohm quad shielded cable i got form a place I used to work, HP node cluster inter connect cable. .405 blue in color, i cant remember the vf on it but i did spec it out a while back, and its ok for HF use. ) Or, tuning the antenna @ the base with a variable cap. of sufficent size, or perhaps even both? I know there is NO magic that can come..im just trying to improve on what I have and can do @ this point in time. Suggestions, thoughts, flames and raised brows are all welcome. Steve Raas N2JDQ ___ Topband reflector - topband@contesting.com ___ Topband reflector - topband@contesting.com
Re: Topband: Looking to improve TX antenna Efficiency
Steven Raas wrote: Main Element: 32 feet vertical - 90 deg bend ( the 'L' ) which runs 43' horzontally pointing north. Then, another 90 deg bend, and ascending 26' in length ( from 30' up to about 11' above ground running from west to east. ), then..you guessed it.. another 90 deg bend that now runs to the south flat top for 27' ( @ 11' up ) This type of question is hard to answer because we don't know what you are able to do. If you are able to do it, I would suggest changing from an inverted L to a T top loaded vertical. This suppresses useless horizontally polarized waves and improves the efficiency in terms of what is heard at the receiving end. You may still need a coil at the base to achieve resonance if can't put out long enough top loading wires. That's OK. Rick N6RK ___ Topband reflector - topband@contesting.com
