Mayhem on AmRad 40 m. band

[Mike Watterson]

In answer to the tuner and power supply questions, both are possible. Discuss.

Yes, though PSUs in parallel is a bit iffy. Better to get a properly rated single one. Also there are hidden issues with PSUs in series, such as 2 x 30V to get 60V. A momentary short can be an issue even if both are current limiting. As an aside I added two protection diodes to one of my PSUs after the "load" damaged it.

Aerial tuners don't tune aerials, unless it's a loop on a receiver. They match aerials. As such if the feed cable is more than maybe 1/8th to 1/5th wavelength, the tuner (matchbox really), needs to be at the aerial end of the feed cable rather than on the aerial socket of the radio.

One situation where two "ATUs" might be in series is if one is a variable inductance to tune whips shorter than 1/4 wave, or exactly 1/2 wave. Few ATUs will tune a halfwave; certainly hardly any of the "auto" kinds. Generally a 1/2 wave whip or wire needs a tapped autotransformer and maybe capacitors right at the base/end of the aerial and that needs switched out of circuit at any different frequency.

The "tuner" built in on a military HF set might only be variometer or series inductance for 6′ to 8′ whips, but you might have a dipole, zepp or other long-wire.

Generally putting two ATUs in series at the radio end won't do much good unless the feed is electrically short and the aerial suits one but not the other ATU.

I had "fun" trying to make a whip / colinear that worked on 6m and 4m. It's nearly impossible compared to 10m & 6m, or 2m & 70cm, or even 6m/2m/70cm (which are either poor on 6m or poor on 2m/70cm, so I have switch (and it adds a series capacitor) on a short whip with helical top for a 6m/2m/70cm handheld.

I'm converting an X X X X fixed circular polarised 2m yagi to have 2 feeds and then a box for | — \ / LC RC modes. The box needs a bunch of 50 & 75 Ohm cables exact size and a 6 way two pole switch.

I considered building a 6m to 4m log-periodic, but getting long enough alloy tubes is an issue. One for 10m to 6m would be more use. A 6m/4m yagi really just needs to be dual band.

160m is an issue unless you simply have a switched series coil at the feed end of a 1/4 wave for 80m.

I have a dual discone, ex military, and it works 20m to 4m with no ATU and not to bad on 80m and 40m with an ATU (but maybe I'm radiating partly on the feed).

A pole mounting end fed dipole (military for 82MHz approx) isn't too bad on 4m (70MHz) with no tuner (none of the tuners go higher than 6m and some only up to 10m).

The FC 40 is good being remote, but fussy what whips & long wires it matches. Sensibly on the the radio you either select none, internal or FC40.
The little Elecraft auto ATU on the FT817ND will tune a CB silver stick on 80m to 6m, but only if you totally remove the tapped matching coil inside the base. Then it doesn't work on a CB, or on 10m without the auto ATU. The FC40 on a FTdx10 doesn't work so well with it (oddly too long!). The custom 4m whip in an extended scrap Watson 300 case (used white plastic conduit on top end and fitted 1m radials) will tune on the FC40 on some bands. I've a relay to swap to a long wire about 20m long.