Topband: Omega-match

[gamma.tec at t-online.de]

Hello all, 

after several tries, I am short before giving up for now... 

Complete story is as following: Lost my last vertical (21m/70ft) in march 04, storm with  
120 km/h/75 mph. November 04 I started to build another one, using parts which are  
liing around here. Finished with main mechanic in december, and its now 26m/87ft  
high. The first 11m/37ft is an heavy-duty aluminium-tower with a lifter, the rest is a  
construction of pipes, starting with 60mm / 2 3/8 " and ending in 12mm / 1/2". Two sets  
of guy-lines, kevlar-like material. 

Picture with lower-part of vertical: http://www.gammatec.privat.t-online.de/tower-r.jpg 

For shunt-feeding I made a construction of 7 Cu-wires, 50cm/20" apart from tower, and  
10cm/4" between the wires. Diameter of Cu-wires is 3mm/ 1/8". Because there is a lifter  
running up and dwn the tower-section, I had to attach the wires at 11m/37ft. End of  
matching wires and the box is 50cm/20" agl. 

match-point at bottom: http://www.gammatec.privat.t-online.de/feed-r.jpg 

The method with little Var-Caps and little power searching the values was easy: For  
80m gamma with 230pF, 160m omega with C-par abt 800pF and C-ser abt 120pF.  
Then I changed the little with better ones out of my junk-box. 80m was really fun,  
working at once, good bandwith on whole CW-section, also no prob with power. 

Picture of box: http://www.gammatec.privat.t-online.de/box-r.jpg 

On this picture no. 1 are the ant-sockets for 80 and 160, no. 4 are two PL-sockets for  
80/160m coax. No.3 is a 200pf Cap parallel with an air-variable-Cap for 80m. But, 80m  
was easy and works well. Later I will replace those 2 times 2 sockets with relays, in  
moment I has to go out for bandchange and change in/out plugs. 
Problem was and is 160m. I tried and burned a lot, Coax like RG213, Aircom+ are  
burned at levels with abt 300W. Doorknob caps are ok, but all I have, up to 7.5 KV, are  
walking with temperature, unusable. The last version of my box is on the picture. no.  
2.1 is a 4mm-air-variable C parallel with 2.2, some meters of 7/8" hardline coax as C- 
par of the match. And no. 5.1 is a 6mm-air-variable C parallel with 5.2, 6 pieces of 7/8"  
Coax which give me 100pF. Both 5.1 and 5.2 are the C-seriell in that omega.  
Last evening I thought this version has to be ultimate and vy ok for kW, the final with all  
that hardline-Coax! 

But here is another picture: http://www.gammatec.privat.t-online.de/7-8-burned-r.jpg 

Yes, really, it happened, I burned that 7/8" hardline, the C-seriell one ! 

Now I do not know, what I can do more, I have some ideas, but not sure what will work. 

-VAC maybe working, but the last one I saw on ebay was a 10KV one, gone for  
136Euro/abt 110$, a bit too much. 
-More Cu wires are not easy to add, but possible 
-raising the distance between wires and tower is not that easy 
-reducing space between wires and tower is no problem 
-attaching the feedpoint higher than now is more work for spring. I has to go then on the  
other side of tower, also only 15m/50ft is maximum, there are the first guy-lines  
attached. 
-using tower for an L-concept is not vy easy here, also maybe the 80m spitfire-option I  
am working on will be disturbed 


Maybe, and I hope so, I am a bit blind now, and there are some other things possible to  
get it working not only with QRP. 

Btw, ground consists of 120 radials, each between 15 and 25m (50 to 83ft) long, also 4  
times 40ft long chicken-wire, and another chicken wire covers the complete area of  
3m/10ft around base of tower. Feeding-Coax is a run of 35m/120ft 5/8" hardline. 



Many tnx for help, and cu on lowbands, André  DF9OX