Feb 15, 2009

Having stuff available

In our hobby it is very convenient if you continuously have all possible required parts available for 'the next project'. This story concerns bragging about pulling the rabbit out of our sleeve on demand. But to be more seriously; this is where we have grown over the years by carefully choosing the right parts, and buy large quantities each time, at flea markets and keeping so called 'obsolete old stuff' conservatively stored instead of throwing it away. Also, if you can build something and it works well, build more of them as they will become handy in time.
But it is not at my place, it is at my friends QTH. His garden is growing all kind of vertical constructions all the time, year in year out.

K9AY and Magnetic Loop
To put PA3FGA's K3 and the all new Perseus to the test, various RX antennas are put up and compared against the short 160m reference vertical in the front garden. There's also a wideband NVIS dipole at 1m70 height available. Mind you, we do test antennas 90% for 160m use.

The K9AY antenna box is my MKIII version. It was build just before a test-weekend on Friday night in total darkness. We started with a brand new version MKIV, which earlier during CQWW CW in 2008 at our PI4TUE club station, showed open circuit 100nF caps. While trying to do the F/B adjustment on the termination resistance, other problems turned up. That's where the available old MKIII antenna box was put in action again. It's nice if you have spares available :)
The second antenna is a simple magnetic loop made from a 5mtr length 22mm dia copper tube. On the top a water bottle (rain protection) contains a strap of doorknob capacitors. On the bottom an FT240-K ferrite with 8 windings inside another bottle holds the 50 Ohm output coupling, followed by a coaxial common mode filter.

The magnetic loop is mounted to a thickwall glass-fiber pole, which in turn rests on a spare antenna rotor. At first it was mounted at 1m from the ground only. This gave it a low Q and thus a relatively wide BW. At this new height the BW has narrowed to a more relevant 20 Khz.

How do they perform?
The K9AY, after careful alignment of the termination resistor, shows 2 to 5 S-units F/B on 160m. Times the 3-4 dB (which is average for S-meters) we get a result which is common for this antenna. This version of the K9AY is our 10th time we have set it up and the 3rd time in this backyard. It is a useful RX antenna in which you can quickly switch in the 'backside null' in 4 directions.
The magnetic loop has narrow nulls off the sides and after some 5 weeks of use it does not show any real advantage over the other available RX antennas (short vertical, K9AY and NVIS).

Let's do 7 MHz antennas this weekend
Not only because we want to listen on 40m but Rens, PA3FGA also likes SWL AM broadcasting on 41m shortwave. He wants a full size dipole, hung from the available glass-fiber pole and a resonant vertical for comparison( actually that last one was my idea). So the K9AY and the magnetic loop have to go.
The K9AY central pole is lowered, the guying wires winded on the cable reels. The anchors pulled out of the lawn and cleaned. The MKIII antenna box removed and all stored in a box for the next possible field operation.
Two lengths of wire are cut for dipole resonance. Now for connecting the central coax a current balun is needed. Let's see what we have in the box?

The ferrite and copper wire were bought from Amidon (or their supplier CWS ByteMark for that matter) some years ago. On the right you see ready-to-use build versions in a box; the white one is an FT240 type 67 toroid and the green one is a type K. The #67 is better suited for 20-10mtrs, the K version is better for the low bands. We used these in our multiband verticals during summer holidays in Liechtenstein/HB0.
The other pre-wound baluns have F150A-K toroids and multi inputs suitable for 12.5/18/25/28/32 Ohms depending on which winding taps were chosen. See the book of W2FMI for details on this. All baluns are XXXL style built and way overrated.

The above balun was our first one build. We used this on a low full size 160m dipole and tested this during the CQWW-CW contest in 2003 on a farmers land and a portable set-up. We made 200 qso's from 21:00 till 00:00 during Saturday night, just for fun! The balun is not black-burned; it is a coating spray against moist. And the little box normally holds...euh held some of the lesser used spices in the kitchen closet.
The 3Y0X hat is only for cold weather protection.
Rens sent in the log and got rewarded by this diploma. I recall that I was the op at that time... oh well today's story was about bragging, right?

The full-size 40m dipole is quickly hoisted up to about 10mtrs AGL and attached as an Inverted Vee to anchor points left and right. Coax was already available from the magnetic loop experiment. A quick check on the network analyzer shows a wide dip at 6.9Mhz. Good enough. The 40mtr band ends at 7040KHz for TX anyway :)
Next we collected the 7mhz vertical+ top loading capacity hat (see my earlier blog from sept 14th 2008) from his garage and put it on the mounting post in the middle of his backyard. This is a fixed mounting location with a 3mtr 22mm dia copper ground pole, some 8 buried radials and a buried Ecoflex-10 coax going to his shack. It has served many, many (test-)antennas already. A 5-minute job only and we are also in business vertically polarised with a perfect SWR.

The right leg of the INV-V is attached to a convenient tower section, which was extended by wooden stick( a spare garden tool). You see, it's always wise to keep also tower parts available!
We had to cut some branches
high up in the tree. These would otherwise tangle up with the other leg.

How do they perform?

On saturday evening the PACC contest is on and we monitor our clubstation PI4TUE efforts on 40m. On large distance contacts their high dipole (@70mtrs AGL) hears Asia and USA better, but on the short to medium distances our lowish Inv-V is clearly the winner. Just as what might be expected. The vertical offers more man-made noise and still has to show its dx capabilities in terms of signal/noise yet. But it is an early first night. We will have to test these antennas for some weeks.

What antenna do we want to build next?
As we are restricted by domestic garden boundaries, the list stops at:
- NVIS dipole wideband (2x8mtr legs@1m70 +32:1 balun) up in the side yard
- Inv-V for 40m up in the back yard
- Short vertical with capacity hat for 40m up in the back yard
- Short resonant RX vertical 160m up in his front yard
- Full size Multiband 10-12-15-17-20m 0.25 grounded vertical up in the side yard
- Short resonant phased RX verticals 160m
- K9AY (several)
- Full size multiband 30/40m 0.25 vertical
- Extended 40m vertical (11m85) with short elevated radials (1/8@4mtr height)
- Full size Multiband 10-12-15-17-20m extended vertical with resonant elevated radials
- Magnetic loop (2 different heights tested)
- Inv-L 160m with 12m vertical part + 2 elevated radials (fire in da hole!)
- Short 160m (23m)vertical with center coil
- Various multiband antennas preparation for field use (HB0-2007&2008)
- Commercial trapped 10-40m vertical (abandoned, bad performance)

The above corner shows some 'spare tools for ground mounted verticals'. The other pic shows some plastic posts, convenient for your vegetable-garden. And for beverages. There are some 150 more in his barn.
Rens is not married. His YL allowed all this in their garden and even recently build a K1, and a K2.
Life is a matter of priorities

I'm going to bed now :)

1 comment:

First aid chick said...

And most recently she put a horse on the front lawn... :)