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Monday, June 18, 2012

Update on Another Portable Antenna

I'm pretty happy with my new end fed antenna. Using it Friday evening through yesterday afternoon I've worked NM, PA and OH on 20 and OH and TX on 30. All on CW from my back deck and 5 watt KX3. While not foreign DX, the contacts have been easy to make. Most answered my CQs. Keep in mind also that most of this time band conditions were poor because of a solar flare/storm.

This one is replacing the 58' wire in my KX3 travel bag.

Friday, June 15, 2012

Another Portable Antenna

Tonight I got on the air with my latest endfed wire and had good success working both New Mexico and Pennsylvania.

I've been concerned about running a non-resonant endfed 58' wire with a single counterpoise laying on the ground. It sort of felt like an off center fed windom with half of the antenna on the ground.

I put together a 20 mtr end fed zepp (14'3" of TV twin lead with the hot side feeding 33'3' of wire) and arranged it as a sloper with the KX3/feedpoint on my deck about 8' off the ground, the twin lead/wire connection about 20' off the ground,  and the far end of the antenna about 1' off the ground. Now the ground side of the antenna system is up in the air rather then laying on the ground. It seems to work pretty good on 20 and as a bonus the KXAT3 antenna tuner can also load it up on 40, 30, 17 and 10. (Not the most efficient radiator on these "bonus" bands but if I can make contacts it is good enough). The reverse beacon system at says I'm getting out.

Besides set up as a sloper (more or less) this antenna can be deployed as an inverted V, an inverted L or a vertical...mostly how ever is convenient to get some part of it up in the air. The 33' 3"portion of mine is Radio Shack insulated 18 gauge stranded copper wire. It runs over tree limbs just fine. Unfortunately Radio Shack no longer sells the light weight twin lead that I used...but any twin lead or ladder line will work but the 14'3"length will need to be adjusted depending on the twin lead velocity factor.

(Just an additional note....where did 33'3" and 14'3" come from?
What I have is a 20mtr EFHW with a quarter wave matching section. At 14.060 MHz a EFHW is 468/14.060 or 33.3'. Even the KX3 ATU can't match this 33'3" wire directly, it is too high of an impedance. The quarter wave matching section transforms the high impedance feedpoint of the EFHW to a lower impedance that the KX3 can handle. At 14.060MHz a quarter wave is 246/14.060 or 17'6". Assuming a velocity factor of 80% gets the length to 14'3". )

(Something else, the  KXAT3/tuner is still needed, even on 20. Nothing's perfect and the twin lead quarter wave matching section can only be said to transform high impedance to low impedance. How high and how low changes with how/where this antenna is deployed. The KXAT3/tuner covers the variable.)

Monday, June 4, 2012

KX3 and a Boat Anchor Amp

A year ago, in a rare foreshadowing of radios to come, I acquired a linear amplifier built around a single 572B running grounded grid. It matched my Central Electronics 20A and the seller
had done really nice job of replacing the four original/modified 1625s in the P&H Electronics LA-400B with a 572B.

Now, seeing it in my shack, I realize that I have a potential May-December wedding here. Sure enough, my KX3 with KXAT3 easily drives the 572B to 100 watts out. The next step is to build a relay box that bypasses the amplifier and delivers -100VDC cutoff bias on receive. It can be controlled via the KX3 Keyline Out signal and a "Keyall" board from Jackson Harbor Press/WB9KZY.

At 35 pounds this one will be a heavy weight. I doubt it will see any picnic table operating but it will certainly help warm up the shack next winter.