S.W.L Dee-Com ATU

[gezza123]

HI Guys.
I picked up a (S.W.L Dee-Com Atu) at Golborne it has a tuning range from 1.8 to 30mHz with 11 taps on the inductor coil in a Pi configuration.
I need to find if the tap connections are in the correct positions, I have searched the web and found lots of Pi configurations but they all seem to be different winding tap connections.
Does anyone have any information on this product please, the only information I could find is as follows, but not found the magazine.
Thank you Gezza123

Title:
Dee Comm SWL Antenna Tuning Unit
Author / Creator: Bunney, R.
In: SHORT WAVE MAGAZINE; 51, 6; 44
Supplier: PW PUBLISHING LTD
Year of publication: 1993
Size: 44 Pages
ISSN: 0037-4261
Type of media: Article (Journal)
Type of material:
Print
Language: No value
Classification:
DDC: 621

[kellys_eye]

The taps would be set according to the users own requirements therefore they have no 'set' location.

[Radio Wrangler]

There seem to be enough inductor taps for it to be useful. It should be an effective ATU for a receiver or even for a few watts of transmitting.

The exact indiuctance required depends on your antenna, but with variable capacitors, you find the nearest tap by peaking the wanted signal, and that'll do.

The settings also depend on the input impedance of your receiver. It's most probable nowhere near 50 Ohms though the manufacturers usually use 50 Ohm connectors.

This atu breaks two rules for good atus:

1) keep wires from inductor to switch short and stable

2) have numbered scales on the capacitors and switch positions

Those appear to be 'AM/FM radio' capacitors with built-in reduction gears so the knob rotated a few times across the capacitor's range. This makes tuning sharp peaks easier but prevents having a useable scale.

You need scales so you can jot down settings you find work for your favourite frequencies. without this, life can be frustrating.

Short wiring helps at higher frequencies.

If you use it with long wire antennae, the left capacitor will have the sharper peak and the right one will feel as if it moves that peak but also changes its height. so sweep the left knob, find the peak. Move the right knob a little and then sweep the left again. Is the peak better or worse? and this tells you the way to work along with the right knob. When you've optimised both capacitors, you may wonder if a different inductor tap would be better.... It's tedious until you find good taps for your usual bands, and this is why you need scales on those capacitors.

David

[David G4EBT]

I recall seeing those ATUs many years back at rallies, and thinking what a needless rats' nest the wiring was. I'd certainly want to tidy it up. It does use air spaced caps, so I guess that as David ('RW') says, it would be good for a few Watts on transmit. Pity the caps have built in reduction gears, which means more than one rotation of the knob, so makes it not possible to calibrate the dials. Be interesting to know to what extent it does peak up received signals.

I did find this in an internet search. Might be worth trying them to see if they took over Dee Comm and have any info in their archives:

KZJ Communications (DeeComm) (Haydon West Midlands), Unit 1, Canal View Industrial Estate, Brettell Lane, Brierley Hill, West Midlands, DY5 3LQ. Tel: 01384 481681

There is also a company called Dee Communications based in Cheshire, that supply two-way commercial radio who probably have no connection.

[Herald1360]

Perhaps a further useful feature would be a straight through option so you can see whether it's actually doing anything worth bothering with on receive.

[turretslug]

Originally Posted by kellys_eye

The taps would be set according to the users own requirements therefore they have no 'set' location.

As he say, twiddle for max! At least it won't harm a receiver. As the others say, it's a shame that there isn't a bit more in the way of logging markings. Two or three decades ago, those receiver capacitors with a 3:1 inbuilt drive could be had for about 50p a pop, I built a spookily similar ATU (after all, there's only so many ways you can sensibly arrange this simple pi-match arrangement!) but with short, direct wiring between polythene overflow-based coil (looped connection break-out taps, not solder-dabbed on...)and ex-equipment switch, the coil was supported on Paxolin cheeks, not left hanging from F+E sockets... I thought that the reduction drive would be a Good Thing, but tuning isn't that sharp and 1.5 turns of the knob gives setting ambiguity. It only takes a moment to peak for the centre of the current band of interest, then nudge it a few degrees for max noise as you tune along. I wouldn't think of using a half-decent radio without an ATU 'twixt it and random wire, but, as Herald says, a simply-fitted bypass switch will provide quick reassurance as to whether it's achieving anything.

[Skywave]

Like others here, I've spent a good deal of time over the years experimenting with ATUs / AMUs. Reading the above and looking at the photos., a few comments spring to mind.

1. The wiring between the rotary switch and the coil is unacceptable - as other here have said. Use thick, soild wire - e.g. 18 - 22 s.w.g., each wire insulated from its neighbours.
2. I would seriously consider replacing that cheap, plastic rotary switch with a ceramic, low-loss type.
3. This device can be used with a so-called 'longwire' aerial. With such an aerial in use + this type of ATU/AMU, a low impedance earth connection (using the provided earth terminal) is essential.
4. A by-pass switch - ATU/AMU in / out - should be fitted. Again, use a low-loss switch.

Al. / Skywave / Jan. 25 //

[dave walsh]

Gerry got this ATU from me and we have been seeking info for ages. I was confident I could find the original advert in SWM or the RSGB mag but no
Gerry posts again and is almost overwhelmed. Never give up eh.
Dave W

[gezza123]

HI Guys.sorry for the delay needs must.

Hi (Kellys eye) thanks for your input, I did not know if the tapping had been put in the correct positions for 1.8 to 30mHz range and if anyone had information regarding the taps for different bands.I have tried moving them about but still not very efficient on some bands
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Thank you (David Radio Wrangler) as always your input is invaluable to me and the forum.
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Hello (David G4EBT)
Thanks for your input, I have rang them as the phone No. and address is on the back of the A.T.U and they are no longer there.But they have passed on another No. for me to try.
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Hello (Chris Heral1360)yes I did try linking out and the unit does make a difference,
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Thanks you also (Turretslug) for your input, I have tested the unit on all the bands and it only seams to peek on 40m and 80m bands.
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Hi (Skywave) thanks for your input, but I dont wish to alter it in any way from its intended original manufacture.as there are not many of these models about I will put it on my keep shelf, its just that I would like to know is it realy for 160m to 10m or has it been modified for 40m and do you know what the inductance would be for the full range of bands, I am begining to think that it may have been overpowered and heated up the coil and may have killed its inductance.
I did read that these coil formers are notorious for breaking down under high input loads.

The inductances I measured shown in the diagram below

Thank you all again for the input.Gezza123

PS: Hello (Dave W) thanks for looking and as I said dont you worry as I still love it and will never give up.
Gezza123

[TrevorG3VLF]

The settings will depend on the frequency and the aerial impedance and the optimisation required. You can get high Q to reduce stations on other bands or low Q for maximum efficiency.

You will need high C1, C2 and L on lower frequencies and low C1, C2 and L on high frequencies.An end fed aerial will have a wide range of impedances. You can use a program (MMANA?)to estimate what the impedance will be and you can then calculate the components required to get the match you need.

[dave walsh]

OK Gerry. At least it's progress [of a sort] even if it needs a complete workover! I'm sure you will "soup it up" into something much better [a bit like the current EC10 thread]. I hope you are not going to claim on the 12 hour guarantee I gave you though
Dave

so makes it not possible to calibrate the dials

At least they are geared so a 'multi turn scale' will work, unlike the ball race type of slow motion.

[Radio Wrangler]

Hi Gerry,

So if you intend to keep it unmolested on the shelf as a sort of time capsule/exhibit, then you're going to need a proper ATU for actual use.

George Burt, GM3OXX introduced me to an superb design which handles unbalanced or balanced antennae. Built with broadcast variable capacitors, it's good for reception or QRP work, so if you fancy doing a bit of building, this design carries George's recommendation, and he's got over 300 countries logged with only 1 watt of output.

Thanks to Dave, dsergeant for pointing me at the right RADCOM

"A Pi-tuned balun antenna coupler for the hf bands - A. S. Chester, CEng, MIEE, G3CCB
RadCom November 1980 p1146 - with photo on the front cover.
73 Dave G3YMC"

A couple of those 1960s style Japanese reduction drives and scales would be perfect.

Cheers
David

[G6Tanuki]

Looking at the coil and capacitors and comparing them with the similar items in something like the Codar AT5 transmitter I'd say it should be happy to handle 10 Watts of continuous carrier-power/CW RF, and maybe 25 Watts AM/SSB.

It's essentially a simple pi-tuner - as such for a given frequency there's no 'correct' settings for the two capacitors and the inductor: these will depend on the impedance of your receiver/transmitter, and the impedance/reactance of the antenna you are coupling to. You may want to choose a lowish 'Q' resonance on transmit to reduce the circulating currents (and so losses) in the tuned circuit, or a highest-possible-Q resonance on receive to provide good signal coupling with additional image/off-tune-signals rejection on the upper HF bands.

With transmitters, there seems to be an unspoken 'rule' to aim for a "Q" of 12 in PA and antenna tuned-circuits.

[Radio Wrangler]

With receivers, going for a higher Q can be useful. On the lower frequency bands, the problem isn't sensitivity but noise, intermodulation and other nasties, so the narrow peak helps reduce the total number of unwanted signals hitting the receiver, and the increased loss is tolerable.

An ATU with three knobs has three dimensions of freedom, and so within limits it can not only be set to mach the resistive and inductive/capacitive components of the antenna impedance, you get to be able to vary the Q over a limited range.

Transmitting, you want the match to be accurate, but tuning it to a high Q setting increases losses, which is not helpful. Using an atu as a means of reducing harmonic output is not good because if a transmitter is dirty, it will be so into any other antennae where you can only get a lower-Q match.

David