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EFHW Experiment Part5

EFHW Experiment Part 1EFHW Experiment Part 2 EFHW Experiment Part 3EFHW Experiment Part 4 UPDATED 2023-03-03 Adding 40M

Adding a linked in tail to the 20m/30m EFHW turned out to be about as easy as you might expect. The 40m EFHW was tuned for 7.100. The other bands could be easily matched by selecting the best match via moving the transformer tap.Â

The links at 20m and 30m will allow a lot of versatility at the cost of lowering the antenna to connect or disconnect the links. Likewise with the transformer taps. So a bit of footwork is the tradeoff for multi-banding. But its not just the band changes. Judicious configuration choices allow the possibility of multiple choices of radiation patterns.

BAND TAP Best SWR SWR range to expect 40m 8.5:1 7.1(1:1) Entire band, (1.3–>1.6) 30m(j) 8.5:1 10.25(1.6:1) Entire band, 1.6:1 with wire drooping 30m(j) 8.5:1 10.1(1.3) Entire band, 1.3:1 with wire pulled taut 30m(j) 7.5:1 10.3(1.4) Alternate tap,1.4:1 with wire pulled taut 20m(40m-tail) 6.5:1 14(1.4) Entire band 1.4–>1.6) 20m(no 30m/40m tails) 8.5:1 14.025(1.4) Entire band favoring CW section 15m(40m tail) 4.5:1 21(1.1) Entire band 1.1–>1.8 15m(j) 4.5:1 21.010(1.4) Entire band under 2:1(wire drooping) 15m(j) 4.5:1 21.010(1.0) Entire band flat with wire pulled taut 10m(40m tail) 6.5:1 28.0-29 Entire band with tap 3 , 2 or 1 10m 6.5:1 28.000-29.25 28.00 thru 28.800 under 2:1(swr 1.2:1 on CW) 10m 8.5:1 28.00(1.4) 28.00 thru 28.75 < 2:1(swr 1.4:1 on CW)

*note1: “40m tail” implies both 40m and 30m links […]

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End Fed Half Wave Experiment – Part 4

EFHW Experiment Part 1EFHW Experiment Part 2 EFHW Experiment Part 3 UPDATED 2021-04-08Transformers???

On a whim I decided to wind a transformer using two FT-140-43 cores. I went with the same 2:1 ratio as the first transformer. SWR testing using this second version showed that all transformers are not equal. The SWR readings taken using the new transformer with the antenna wire as it was trimmed with the larger transformer did not have similar results. It turns out the new transformer would require re-trimming the wire lengths to bring the 40m band into the same SWR curve. Since I had the 80m coil&tail attached using .250 quick connects, it was easy to add wire. Doing that allowed bringing 15m and 10m to good matches. 20m also found a sweet spot but only on the 6.5:1 tap.

New Version?

Without re-tuning the wire no good matches were obtainable on 40m. Instead of making any permanent changes to the working 40m loaded antenna/transformer combo I am making a different wire based on a 30m wire length. It will include a quick connect to allow the antenna to cover 20m by detaching the section of wire beyond the ~34 foot 20m wire length. That will provide an antenna capable of 30m/20m/15m/10m. This may become a simple way to add a permanent 30m antenna in the w4kaz antenna farm.Â

Maybe I get ambitious and add a second link to include 17m, just for grins. Does an easy tune 30m/20m/17m/15m/10m antenna sound good? […]

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It Is Alive. W4KAZ Skimmer Back In Service

After a couple of months of dead air time, the W4KAZ skimmer returned to service on 2021/4/1. The basement area housing the skimmer station required overhauling in order to replace the leaky old water heater. After repairs, the project to return the skimmer system to service was delayed by other issues. Foremost issue was lack of ambition to tackle the organization project spawned by tearing apart the shack. Oiy.


Part of the re-org was to add in a new shelf rack, and put all of the shelving on casters. The area is also used for general storage. Being able to wheel all of the shelving out into the garage will make access easier all-around.

The skimmer SDR was also found to have a dying cooling fan, so there was some delay acquiring the replacement. Also some of the old input feedline system was replaced.Â

This was also a good chance to downsize the computer system used to run the SDR.  A “new” micro form factor system was acquired, a refurbished Dell i5 in a teeny 8x10x2 box. That’s a huge improvement over the desktop tower sized system previously in use, and the space savings will be appreciated. The new system has a slew of USB ports, but little else. The desktop box will be stored and can be swapped in if needed as a backup.

Skimming System

The skimmer as currently being run still consists of the Red Pitaya used as an SDR, with the 160m […]

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