Mayhem on AmRad 40 m. band

[PerdioPal]

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

[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.

[AmadeusMozart]

The build in ATU in the rigs are imho only good to make the transmitter happy in case of a slight mismatch. Most rigs will not tune much above 1:2 or 1:3 althought the Elecraft K2 was 1:10.

I'd the Collins 180S-1 ATU in the past - that literally would tune anything. I sold it - bad move. At the moment I'm collecting parts for a balanced L-C ATU. Hardest part was finding some capable switch to move the capacitor from the transmitter to the antenna side.

I don't trust power supplies without over voltage protection - I'm at the moment repairing a 35Amp one for a friend and the SCR has fused protecting the gear behind it.  Without the SCR the voltage was around 23 Volts, not healthy for some 12V equipment. 

Don't know how the switched mode power supplies behave in that regard, might make an "outbox" with a SCR and a 15V zener to do the same as that would trigger protection around 15.5 Volts and most car alternators can charge around that level.

73's

[Mike Watterson]

Yes, the T1 is amazing compared to the big beefy FC40.

The big issue with a home brew manual ATU, like the one I had on the FT101ZD, is that the voltage on on or other of the variables caps can get massive.
   
Simple ATU needing wide plate spacing on caps. Allows a short (can be vertical) and long wire, which is the simplest way to cover 160m to 10m.
Used on FT101ZD.

I think based on KW107
   

The Auto ATUs are different
Yaesu FC 40
   

Elecraft T1
   

(All schematics from the makers site. except the KW107, which is vintage.)

[Mike Watterson]

Elecraft T1 https://elecraft.com/products/t1-miniatu...ccessories
Yaesu FC40 FC 40 page

[AmadeusMozart]

The ratings on most automatic ATU's are for SSB or CW duty cycle (50%) and then there is also the listening 50% of the time. Hence if there is a continous data transmission they may only be capable of something like 30% of what their "official" rating is.

I'm now into balanced tuners but I'm very fond of the Collins 180S-1 ATU for end fed - I'd one and sold it when I abandoned HAM radio. I actually have the parts for two - one for the lower end of the HF bands and another for 30 -10. For the 160 -80 - 40 I've got a NIB unused Hammarlund TCD-240-J instead of the vacuum Jennings capacitor. It's a dual 250pF 4.25kV and dates back to 1946! If the box only could tell the story where it has been all this time. For the 30 - 10 I've got a E F Johnson 150F20: a 160pF, 2kV to be used as the output shunt capacitor.

Also found three NOS 1kW , 2 kV 2 poles, 11 position ceramic switches. Price was too good to pass them up, they were the remnants of a business that has closed. Don't know yet what to do with them, might use one for switching the capacitor from input to the output in a balanced L-C ATU, have got 3 Le Pointe 10uH inductors, two NOS, one used and a Cardwell 10uH. That would give me also some interesting options like making a balanced L-C-L tuner. (the "Annecke")

I'm guarding my stash closely - these items are harder to find and the ones that I do find in good condition are often estate sales and have been closely guarded. Plenty of rubbish around that I will not touch with a bargepole.

Making antenna's and ATU's is about the only thing left for amateurs these days, the rigs themselves have become too complex to fix and even when capable of fixing one may not have the right software to adjust everything.

At the moment I'm investigating the best choke for the balanced ATU - only limited choices locally available both in size and in composition. I'll have to stack some toroids to get to a comfortable power level (want to be able to handle 400 - 500 Watts although I'm only using about 50 watts output).

73's

[Mike Watterson]

The ratings on most automatic ATU's are for SSB or CW duty cycle (50%) and then there is also the listening 50% of the time. Hence if there is a continous data transmission they may only be capable of something like 30% of what their "official" rating is.

I think it also depends on type and amount of mis-match. The current and voltage on each of the parts, which is often more critical for the capacitors rather than transmitter power. The coils and switch contacts are mainly limited by current. Obviously the "finding a match" (aka "Tuning") phase needs to be done at the lowest power that system needs for measurement to work, especially to avoid stress on the relay contacts, apart from not annoying other users of the frequency.

The T1 seems tiny but certainly isn't going to "wear out" on a QRP rig (5W) as it's rated at 20W. The FC-40 seems huge and internally not as cramped. Even knowing the ratings of the capacitors doesn't tell you what the power handling really is, but you tend to get catastrophic failure of the capacitors and they are easier to source and replace than the coils or relays.

Capacitor failure in the base seems to be the most likely failure of multi-band VHF or VHF/UHF whips/base verticals, though corrosion can be an issue.

[Murphyv310]

Hi
Interesting discussion. I've an FTdx-10 & FT991A, My FT-818ND is up for sale.
I was very surprised to see the tiny Omron latching relays in the FT-991A the same as in the tr(u)SDX kit radios, I wouldn't have thought that they would handle much but certainly on the FTdx-10 the power is automatically switched to 5 watts on tune. The FT991A was obtained for £650 as the seller said there was a fault when trying to match on 40 meters. I tried a 100 ohm dummy load and it turned fine, so most likely his antenna was the problem and too far out for the internal AMU to pull in, the radio is fine as far as I'm concerned.

[AmadeusMozart]

With all the different bands it has become harder to create an all multiband antenna and a "random" length dipole or open loop can be matched to most, if not all, bands. The "random" lenght is actually not that random as there are certain lengths that are multiple of the higher frequencies and will present loads that are next to impossible to match: one wants a length that sits between all the bands. And then a balanced ATU comes into its own, unfortunately due to the costs hardly anyone is building a true balanced ATU and a balun at the output of the ATU going to the antenna is not going to cut it.

@Murphyv310: You certainly picked up a nice 991A at a good price. Just shows that a VNA antenna analyzer is a great investment, especially at today's prices, and might have shown the seller that his antenna was not tuned properly.

[PerdioPal]

Years ago there was an HF antenna design in WirelessWorld that was sections connected by resistors, OK not very efficient, on receive the atmospheric noise wiped out that bit, transmit, just add power.