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Wednesday, 11 October 2017

Remember DENCO / Q-MAX coils

Remember DENCO / Q-MAX coils from the 50s/60s ? Using 3D printer to make them. Finished coil + data. STL files soon.

Saturday, 7 October 2017

23cm and 70cm yagi antennas in workshop are toast...:-)

In the workshop looked for the antenna bits for the 23cm transverter to find the 23cm antenna (and a 70cm one) had basically been crushed under some items that I had 'stored' in there... oops! So rather than try to fix as the booms were well mangled I am going to try to make from scratch.

Following I am going to basically try and create a short 23cm antenna on a Ali boom using welding rods and a length of 6mm copper tubing (was from an A/C unit I think).

I will use a copy of the DL6WU spreadsheet I have from previous as that site's link doesn't work now.

Copied from that site... I'll basically use materials I will either have to hand or will get. YEs understand 1mm out on the length is MHz so test of my skills.... Semi rigid hardline I have a few options for the matching section.

"Design criteria
There are lots of designs available for yagi antennas. Guenter Hoch DL6WU has researched this subject for decades, nowadays his design formulae are accepted throughout the world in both commercial and home made antennas. Many other designs are actually just small modifications of the DL6WU formulae. In the past I built a couple of 2m beams using DL6WU’s design, so I decided to use this again, now for my 23cm yagi. I started with my design criteria:
  • Center frequency: 1260 MHz
  • Bandwidth (3 dB): 1240-1280 MHz
  • Gain: 10 dBd or more
  • Polarization: horizontal
  • Mount: in front of mast
  • Lightweight


Because of low weight and easy handling I mostly use aluminium to construct VHF/UHF antennas. This material is also easy to drill, saw and grind. You can buy it in most DIY shops. For this antenna I bought an square bar (15x15mm), made of aluminium, length 1 meter. At one end I mounted a standard available mast mount, leaving about 90cm for the actual antenna. Using the DL6WU formulae, this results in a 14 element yagi, with a gain of over 13 dBd. I used the DL6WU spreadsheet calculator of DF2CK to calculate all measurements. I used AlMg3 welding rods for the radials. These rods have a diameter of 4 mm. The dipole is made of 6 mm2 copper wire, matched with a matching loop (1/2 wavelength coax or semi-rigid) and mounted to a female N connector.
These are my inputs for the spreadsheet:
  • Frequency MHz: 1260
  • Boom diameter cm.: 1.5
  • Element diameter mm.: 4
  • Element Thru Boom (“Y/N”): Y
  • Boom Length (Metres): 0.89
This spreadsheet returned these specifications, the real specifications will differ a bit, but it will give you an idea what to expect:
  • Gain: 13.6 dBd
  • Usable bandwidth: 1234.8 to 1285.2 MHz
And it returned these element sizes:

FT8 & 160m qrp?

Just for fun (isn't all amateur radio?) as the nights start to draw in I am going to see if can build a pseudo auto 160m qrp station for FT8 based on (WSJT-X Version 1.8.0-rc2) and, have it running through the winter on 160m (when I am in the shack anyway) so that it kinda makes automatic qso, calling CQ of course not S&P... I wonder how long it would take to work a few DXCC qrp? Yes I know it doesn't do this automatically I will have to augment the source to do this.

Might even use a Wellgood loop for the 160m RX. Inverted L for the TX antenna.

This has already been looked at by a few and I think there are Windows 'capture' versions out there already. So I'm going to see what can be done using the Linux version. wsjtx-1.8.0-rc2.tgz

Looks like will need a homebrew SSB TX (maybe the qrp2004, but just 160m)  and and a dedicated laptop.

Friday, 6 October 2017

xtal TX for PA testing

Odd request in local club but was asked could I build a couple of 1W TX using xtals (NOT DDS etc) for 14.040 and 14.050 as a couple wanted to test IMD performance of their PA. You input both at same time and watch the output for harmonics etc... they had used large TRX to generate the signals.

Anyway seems easy enough  and will allow me to add to the test kit. So after checking the workshop components I will use the GQRP designs and the VU TX version and building a pair on tiny 4cm x 6cm prototyping boards I had been sent a while back.

The 2N3866 I'll use a GQRP club transistor (from 2006 (ish) Jan/G0BBL).

All transistors will be heat sinked as I expect this will be running 100% duty cycle for a bit.

Will probably not bother with the LPF as this will be used in testing not on air.

Photos and oscilloscope outputs to follow.