75m Am Transmit and Receive System
Submitted By Tom K1JJ
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Hi Jim,
Glad you tuned in.
That's a decent receiver and antenna. The problem you may be having is that a dipole at 30' is mainly a high angle radiator. On most nights the west coast comes in at a low angle.
It may be unrealistic for you to do there, but if you could get your G5RV up at 60' or higher it will be easier to hear the west coast under marginal conditions. Though, some nights you will have no problems at all.
Please check in next time you hear the gang on!
Here's a description of the transmit and receiving system I currently use on 75M for the west coast, USA.
The Yagi:
It's a 2 el 75M wire Yagi with a parasitic reflector - beaming 269 degrees west to Los Angelos. (I took a transit North Star fix reading before erecting the 2nd tower) .. :-)
The driven el is fed with coax and hardline, coax coiled balun, 122' long. The reflector is 128' long. The spacing is 36' apart. Works well from 3750 to about 4.0mc.
Vertical takeoff angle about 28 degrees. Beamwidth about 80 degrees -From CT it covers about from Alabama to Washington State, centered on LA... (3 db points)
Supporting Structure:
The whole structure is flat, horizontally suspended tightly between two towers at 130' off the ground.
I used two tapered 36'long aluminum ~3" diameter poles as "bridles" with one attached horizonatally to each tower. These bridle/poles each have a pulley and rope on the ends to permit raising and lowering of each element. They keep the elements perfectly spaced 36' apart and flat...textbook Yagi picture.
Each bridle has an overhead truss (cable) that attach it to it's tower to simply hang and sway...no torqing on the tower this way.
Perfomance:
I find that for the area between the Ohio and California the Yagi is between 8-15 db better than the reference dipole at 50' on transmit and especially receive. However, within 300 miles the 50'high dipole is ALWAYS louder...sometimes as much as 15-20db.
Receiving System:
I also use an 800' long wire beverage antenna heading west with a 600 ohm terminating resistor at the far end to ground. It uses a 9:1 toroid balun to feed it, so is broadbanded from broadcast band - 14 mc. It has a f-b of about 20db when checking off the back to Europe.
When listening to the "DX" Amers out west, I don't use the hi-fi SP-600, but rather the two receivers in the FT-1000D. I use stereo headphones and connect the west beverage to one receiver and the other receiver to the west Yagi. I modified the FT-1000D so that one VFO controls BOTH receivers in perfect tuning sync.
With the stereo headphones (two receiving channels) there is a true diversity receiving effect. The Yagi and beverage are totally different (height, distance between them, etc) so that each will have phase peaks and dips at different times. When in-phase I hear a wonderful stereo effect of the station sliding back and forth between the ears. When the antennas fight each other there is always one that dominates and do not seem to lose the signal due to fade.
BTW, the beverage is VERY close to receiving par with the Yagi! I would encourage anyone with the room to try a terminated beverage - make it at least 400' long....with 2000' being the max. The longer, the lower the receiving vertical angle and the narrower the beamwidth. 1000'long is perfect for east to west coast on 75M, 6'-8' high off the ground. It's better to make it lower than higher.
I must say that after trying countless antenna receiving systems designed specifically for 75 AM west, this dual diversity system is by far the best. For the first time I have the confidence to encourage low power, modest antenna AM stations on the west coast to come on in and give it a try... fun- fun!
73,
Tom, K1JJ