Building a 4 element DK7ZB Yagi for 50 MHz

As I had build the 10 element Yagi for 144 MHz and had good results with it, I wanted to exchange my simple 6m (50 MHz) dipole as I could not really DX with it. It was only used for monitoring propagation openings.
The website of Martin DK7ZB has many designs and I chose for the 4 element version.
Reason of this choice is that it is only 3 meters long and was not to interfear with my 144 MHz Yagi, which has to be able to elevate for EME work.
The 3 meter long version does not have the maximum gain but as I could not place it in a free space, I had to take the radiation pattern in concern.
The antenna could only be placed just above the roof and this is not the best position :-)

The elements are made of 12mm aluminium tubing, 1mm thick. The element holders are from Nuxcom Germany and I just use two per element for better mechanical great!
The boom is 12 x 12 mm aluminium and does not need to be larger as it is only 3 meters long. When building longer Yagi's you need a greater diameter boom or support bars underneath as I did with the 144 MHz version.
Element with 2x plastic element holder from Nuxcom, which can be used for 6, 8 or 12mm elements;

The dipole on the DK7ZB pages was mouted above the radiating element ...strange, as it is not easily made waterproof. I chose for a own construction:

The plastic box is from the local do-it-yourself shop for electrical wires. I used a grey 16mm electrical pipe as isolation for the radiating element to boom construction.
Only use the grey type, it is UV proof and hit proof ...does not break easily when you strike it with a hammer and does not effect the RF fields.
I also use this material for vertical VHF and UHF antennas.
Inside are the two 400mm long 16mm diameter aluminium pipes, which have a cross slicing at the end (done with a hand saw) and you put a hose clamp16mm over it.
When tightning the hose clamp, the 16mm tube becomes smaller and fits strongly on the 12mm tube which is inside it. See photo for better idea.

The balun is made of 2x 50 Ohm RG-58u coax cable parallel and length is 1 meter. The dipole is 12,5 Ohm at center point and has te be converted to 50 Ohm for our coax cable connection. See the DK7ZB website.
It is connected as shown on the photo. I drilled two holes in the grey plastic pipe so it would maintain its strength and I could connect the coax to the 16mm aluminium tubes, which are inside it..

The PL259 or N-connector is sealed with an O-ring to make it waterproof, between the connector and the plastic box.

The mast clamp is also a home made design. I use 4mm thick aluminium plate. I also use 48mm U-clamps for mounting against the mast. These are also used in the car industry for exhaust pipes.

The tuning for best SWR is done easily. I put marks on the radiator element halves for every 5mm. This is done so each half is moved in or out the exact same length to keep it symmetrical.
The SWR is tuned exactly 1:1 and the needle of my SWR meter does not move on maximum sensitivity !!!!
Bandwidth with SWR 1:1 is 75 kHz and easily usable for 350 kHz (50.000 to 50.350 MHz)< 1:1.5.

Some quick statistics for DX made on 2-7 & 3-7-2009 in CW are V29JKV & CU2JT, and in SSB are TF8GX & 7X2ARA. heard in CW was also 8R1TO.
So of course sporadic-E makes it possible to make these qso's, but I would not have made them on my old dipole !

Logbook view of the month juli 2009 by PA3FXO:

01-7-2009 EA7CU M86SU 1786
01-7-2009 UX1UA KO5CO 1780
02-7-2009 GI8SKN IO74DR 736
02-7-2009 EI7IQ IO53LT 926
02-7-2009 V29JKV FK97 6813
02-7-2009 CU2JT HM77ES 2828
03-7-2009 EA8YT IL18SL 3151
03-7-2009 7X2ARA JM16MS 1713
03-7-2009 TF8GX HP84RA 2040
04-7-2009 ER1SS KN46JE 1872
04-7-2009 EC8ADW IL28QA 3117
04-7-2009 CN2AB IM63IR 2256
05-7-2009 PC6M JO22 54
05-7-2009 CN2KD IM63NX 2216
06-7-2009 SV9GAV KM25EH 2441
06-7-2009 SV9CVY KM25KA 2493
06-7-2009 OM5MZ JN97BW 1074
06-7-2009 HA8UJ JN96TW 1229
06-7-2009 UX1DC KN18DP 1313
06-7-2009 EA5CXL IN9XA 1393
06-7-2009 YO7LCB KN15OA 1578
08-7-2009 K1TOL FN44VG 5356
14-7-2009 UT2XQ KO4IG 1688
14-7-2009 UY1HY KO6MA 1991
14-7-2009 EA8CQS IL18AT 3188
14-7-2009 SP7BUZ KOHU 1120
14-7-2009 TA7OM KN9UX 2923
14-7-2009 EA3AR JN12DB 1134
14-7-2009 EA1SB IN72FO 1302
14-7-2009 EB5CNK/P IN9UB 1393
14-7-2009 EA2DLM IN91NP 1237
14-7-2009 EA9IB IM85NG 1966
15-7-2009 CU3EQ HM68KP 2858
15-7-2009 CU1EZ HM76KW 2863
15-7-2009 9Y4D FK9 7423
15-7-2009 9Z4BM FK9GE 7485

Cees PA3FXO 23-7-2009