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Seductive serendipity / Verleidende serendipiteit

January 28th, 2008

CQWW 160m CW-contest with PA7FA and PG0A

OK, here is the picture: the CQWW 160m contest and my recent experiments with K9AY-loops, of which Gary K9AY (also active during the contest!!) himself wrote:

“The changes are good ideas. I also stopped using an autotransformer and do not use the +/-/AC control voltage. When I added a 3-relay termination adjustment, separate control wires were required, and I also put the direction control on that cable. This allows me to use a preamp that is powered via the coax. There will be a product review in QST soon, describing the Array Solutions product that uses my design. The information on RF chokes is very useful. I have seen the power supply problem before, but it is usually fixed with a good EMI filter on the AC input. However, in the past, I have needed a larger RFC as PG0A has discovered. With DC control voltage, this is not a problem, and I typically use a 220 uH RFC. 73, Gary K9AY”

Richard PA7FA and Remco PG0A wanted to test their 160m setup, strategy, and ideas during this contest. That is, not fully participate, but experiment, and see how we can learn. Our goal was to beat Dutch stations in pile-ups, and to ‘DX’, i.e. to work DXCC countries and experience the propagation during a fully saturated band. Nice aspect is that you can sleep during the day ; -)

160-shack.jpg

We prepared the following (Google Maps overview here) setup (click on the picture to enlarge the shack ; -) :

- inverted L TX-antenna with a few radials, and 10000 sq. m. of aluminium greenhouses
- 250m US Beverage, made of welding wire, 4 bamboo sticks, a tree at the other end, and stretched with a bucket of stones.
- K9AY-loops
- ICOM PW-1 amplifier
- ICOM IC-756 pro 3 (I think .. ; -)
- N1MM logging software
- headphone (<- mandatory!!)

The setup functioned very well and we think we were the first Dutch station that evening to work into the US (VY2KM not included ; -) with K1LZ @ 22.21 UTC. Our ‘competitor’ PC5M logged their first US station for that evening (W2YE) @ 23.34 UTC, one hour later (!)

Experiencing this contest, I think it must be possible to work your 160m DXCC within one weekend.
Nice contacts were MD4K, UP0L, T77C, OH0Z, CU8A, CT9M, 4Z4DX, EA9EU, ER5GB, TF4M, 7X0RY, CN2R, C4M, VP9I, KP2M, TA3D, and XE2S.
Statesside we worked about 50 stations including K9AY himself. (Sorry Gary, you were louder on the Beverage ; -)
HK1X and C6ANM were actually the only two stations heard that couldn’t be worked before I fell asleep @ 02.30 UTC.
We did not hear Japanese stations that evening but worked JT1CO (!) easily.

The next evening we gathered a few new ones like 4L2M, JH4UYB (!), IS0OMH, a lot of EU and some new US stations.
Our score will not be high but N1MM showed 204/27/63, i.e. 204 contacts, 27 ?? and 63 mulitpliers??, resulting in a 116820 points claim.

We considered the experiments to be very promising and perhaps we will participate in the 160m SSB contest too.

January 12th, 2008

PG0A implementation of K9AY loops

9:1 transformer
During my preparations for the PACC contest I made some K9AY loops. It is generally recognized that galvanic separation of the loops and the receiving system is highly recommended to decrease interference, noise, and other strange phenomena. The original K9AY design used an 9:1 autotransformer, and voltages to switch the two relays are fed through the coax. Both on the internet and in ON4UN’s Low-band DXing book, usage of a galvanic separated 9:1 transformer seems to coincide with the loss of the initial, and elegant solution to switch the relays via the coax cable.

Noise/interference from the control box
Reported noise/interference when positioning the controlbox in the ‘NW’ position may be the reason for this. In this position an AC voltage is superimposed on the coax instead of a DC voltage. What actually occurs, is that the mains power supply (220V here), with a lot of ‘superimposed’ interference from connected equipment, is almost directly ‘transformed’ into the receiver when the switch is in the NW position (!) In the SE (+V) and SW (-V) positions rectification with subsequent derippling shortcuts this mains power interference.

I also experienced an increase in noise/interference with the switch in NW position initially, but as far as I could ascertain it disappeared when using the ideas below.

AC/DC blocking choke in control box
I think that the inductance of the original choke (in the original K9AY-article 100 μH) is insufficient for the range 0.5 – 3.5 MHz. In my control box I use a 22 mH (Farnell) choke I had ‘in stock’. Its reactance @ 1.8 MHz (XL = 2*pi*1.8E6*22E-3 = 250 kΩ) is of insignificant influence compared to the original 100 μH choke (which reactance is -of course- 220 times lower).

PG0A’s Law: Listening is feeling
I think that a 1 mH choke will eliminate interference/noise most cases. However, I have not experimented with this. To assess the noise/interference, put your receiver into AM mode, dismount the coax towards the loops from the control box, and place the switch into the NW position. Compare it with the SE (+V), SW (-V), and NE (0V) positions. Besides some clicks (AGC effects due to the change of super imposed voltages which (dis)charge the DC-blocking capacitor in the control box) no (significant) increase of interference/noise may occur.
If you feel this is not the case (PG0A’s Law: listening is feeling ; -) increase the inductance of the choke significantly. With my 22 mH choke, all four positions (NE, NW, SE, and SW) sound equal. This was not the case when I used a 100 μH choke.

Another idea, which I haven’t tried yet, is to use a mains AC filter (e.g. from an old computer -switch mode- supply) in series with the power supply transformer.

LEDs on the switch box
Experiences from last year, while building and testing the loops, urged to have some kind of indication which of, and in what direction, the loops are pointing or to assess ‘remotely’ if anything switches at all. So, I replaced the (rectifying) diodes with LEDs, assuming that the relays draw between 15 – 25 mA of current (well.. they do and so do yours ; -).
By the way, I use DPDT 5V relays to compensate loss of voltage when using large lengths of coax as the loops have to be placed far away from the TX-antenna. And.. I have some ideas to create more than four states on a single coax to switch the Rterm value too in order to ‘optimise’ the nulls.

Pictures!
Below you’ll find the schematic diagram. I also made detailed pictures of the contrapsion, controlbox, switchbox-v1, and switchbox-v2. The difference between v1 and v2 of the switchbox, besides the Rterm switch, is the transformer used.
Switchbox v1 used a toroid and v2 uses a binocular version with teflon isolated wire.

pg0a-k9ay-small.jpg

Control box
I have been asked to publish the diagram of the control box. My implementation, depicted below, is identical to the original K9AY version except that the ‘AC/DC’ blocking choke is 22 mH, and I don’t like fuses.

controlbox.jpg

Rocket science?
My initial feelings concerning the aforementioned were that it was not ‘rocket science’ but ‘handy’.
However, my ex-collegue, friend and 160m guru Kees PA0CLN was really surprised with my LED ‘invention’.
“You really should inform Gary about this”, he said. I told him about the galvanically separated transformer, the enormous loss of interference, the single coax solution, and that everything really worked well and so on.
“But how to you feed the relays via the coax cable then?”, he asked.
I promised him to mail him my contrapsion but I thought it would be a nice idea to publish it here : -)

Does it work for you?
Please find out if the above is reproducable, and leave your feedback here.

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