Radio W4KAZ

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2021 WPX CW on 40m EFHW-[Extending a 40m EFHW as an 80 Vertical]

Very casual

The wpx operation was very casual.  I spent a lot of the time just tuning around the bands listening.  The beginning of a CW contest are always too fast paced for my mediocre CW skills, and taking a mental picture of band conditions was more fun.  The bands sounded “brighter” than at any time in the past couple of years.

As a quick-n-dirty mod, I used a second feedpoint to attach the efhw to an 80m folded counterpoise. This is to allow 80m operation by shifting the feedline and using a jumper to bypass the transformer.  \/expanded description below\/  This gave the antenna resonance on 3.625Mhz.  To drop the resonance into the CW segment I wound a 6 turn coil on a 1.25 inch form.  That is inserted at the bypass jumper with faston connectors.  To raise the resonance to somewhere near 3.8Mhz a 3kv capacitance of about 500pf does the trick.  80m was good-to-go. 

Dirty Tricks Department

So as luck would have it, the good band conditions made testing on 80m less useful than I hoped.  20m was open until at least local midnight (0400Z), and probably was open to somewhere all night.  On Friday night few ops moved down as far as 80m with 20m and 40m providing a bottomless pit.  It did allow for gathering some info from the RBN spots, which look like either the band was open in famous fashion, or the EfHW was doing a decent job.  Maybe a bit of both, as the 80m spots looked pretty good, as well as showing up on some skimmers not normally hit with permanent inv-vee.

The antenna was also able to work most of the stations heard on 10m.  That’s a change over the few other recent outings.  15m was a bit of a mixed bag.  20m responses were comparable to other experience with dipoles.  40m seemed unusually good, but it may be more due to the very quiet sounding band conditions.  On Sunday a short 40m run coincided with the band opening to Europe, and it is shown in the RN spots.  The RBN spots started out as US only.  By the end of the 60 minute run there were several EU RBN stations showing 20-30db SNR, and a slow growth in calls from EU stations.  Too bad the contest was at its end.

The 80m Inverted-L Mod

The first attempt to use on 80m, the transformer was shorted out of the circuit and the radial attached to the ground lug.  This did not work as expected, and more testing is needed,  The first thought is the EFHW 120pf capacitor to ground needs to be removed from the circuit for the vertical.  The quick field expedient kludge was to move the coax to a feed point not sharing ground with the EFHW box.  The first test used a single radial cut for 80m. In that configuration the antenna resonated a bit below the 80m CW band segment.  Resonance could be shifted upwards by inserting a series capacitance at the base of the driven element.  SWR was very favorable at each resonance point chosen with about 150 to 200 kc of 2:1 bandwidth.

A second option was tested, using a folded counterpoise instead of the single full length radial.  In this configuration resonance was at about 3.625Mc.  A 6 turn coil inserted in series in the driven element dropped resonance to 3.54Mc, and capacitors can be used similarly to raise resonance to upper SSB band segments.  In this configuration the best SWR was about 1.8:1, and bandwidth more limited.  Easily stretched moderately with an antenna tuner.

The folded counterpoise version was used in the contest with great success.  This is going to require a lot of testing to decide if either version is a better 80m performer.  For my purposes, the FCP version is compact and easy to set up, so it will be the one used.

Potential next project: using relays to allow remote switching, both for the transformer taps when in EFHW mode, and for switching components needed to operate as a standard vertical.  Hmmmmmm

????photos coming 2021-07??????? 


The kludgy fix for adding 80m was an outstanding low effort method for stretching the single driven wire to use on another band.  The cost is the time used adding the FCP radial on deployment and later some manual band switching while operating.  It would not take a lot of effort to add a few relays to allow remote switching – a possible future project.  This EFHW would make an outstanding option for quick deployment by folks stuck in enemy territory where permanent antennas run up against tyrannical HOA rules.  The whole thing can be deployed or removed easily in less than 15 minutes with a bit of planning and practice.

Having a tapped transformer allows a very good match on each of the five main bands of interest in contesting.  I think using the 80m option using a folded counterpoise and 40m EFHW driven element as an inverted-L vertical the seems to be at least comparable to the version with the loading coil and 80m tail extension.  It is easy to deploy and switch, and inserting a small coil at the base was easier than tuning the 80m loaded EFHW.  An 80m FCP is 32 feet long, so it is fairly compact also.

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