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Tuesday, 24 October 2017

Two new 4sq 40m and 80m

Building two new 4 SQ.
One for 40m other for 80m.
Starting off with SJ2W's pcb and will go from there.






Relays are DPDT, 250VAC, 8A versions from Farnell Code 1629053 so far have been good to well over 400W so use for SDR RX and QRP TX shouldn't be a problem.

The torroids T225-2B I have already and several 500V SM caps, again over kill for QRP.

The SO239 were from a batch buy so decided to use all 10 in one go. Just tacked in place for now until I finalise the enclosures, I have several of same type used on E51KTA trip but not sure about UV stability, Might invest in some dicast or IP56 ones.

I'll add the rest of the components once I have the switch and dummy load/power meter sorted out, the signal I'll feed into an Arduino Uno or Nano I expect to do the power measurement.

These will be remote switched for the direction (the relays are not latching type so will need to have them energised for use) so I'll be using USB and Arduino to create the switching voltages.
I might add a sense so can sample the frequency, not sure what value that might be though.

Poles will separated by 1/4 wavelength and will support 1/4 wavelength 40m and 80m ground planes (Poles fibreglass 10m and 18m), wire elements 2mm I expect. Extensive radial matt. Will probably put the antennas up splitting the 4 points of the compass to get reasonable coverage.

I expect I might experiment with a 5th central GP and see what difference that makes.




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 http://www.pa3hcm.nl/?p=650 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

Construction

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) https://physics.princeton.edu/pulsar/k1jt/wsjtx.html 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) https://groups.yahoo.com/neo/groups/qrp2004/fileshttp://myweb.tiscali.co.uk/qrp2004/  and https://groups.yahoo.com/neo/groups/qrp2004/files 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.

Wednesday, 20 September 2017

SDR and Heatmap

Not new but if you are either suffering EMC/RFI etc or just want to see how you or something else is doing you might like to note this software and comments.

https://www.rtl-sdr.com/creating-signal-strength-heatmap-rtl-sdr/

https://www.reddit.com/r/RTLSDR/comments/2hbjyt/gsm_heatmap_using_rtlsdr/

I am sure many know it (dangerous assumption?). It will give you the option of scanning between a start and stop frequency and recording the location. Obviously, location depends on a good GPS RX and satellite visibility and if trying to scan the whole of the HF/VHF bands it is going to take a while but for a small 500KHz section of say 70cm it works fine so you can drive at more than a crawl. 

I used this along with a cheap GPS puck (ebay) and an RTL USB dongle (£10 from some rally), plugged into a laptop, mag mount (ebay for a 2m/70cm elcheapo one) on the roof, puck stuck to the windscreen and drove about and created a map of 70cm signals locally for an amateur
(who had an idea is was a pair of SRD TX 100m up on a pair of cranes already). The signals were blocking the output of a local repeater (20 or so miles away). After a few locals had used contest level beams from a distance to sort out the location to a few 10's of metres, I drove about the location and created a heatmap.

Anyway... it can help ID a noise source location, and/or where the signals are RX so might help some sort out interference. I have not tried but I suspect a suitable antenna on a car and a scan of one of the VDSL 'steps' from the recent VDSL survey and a drive about a village etc might be interesting.

I might write it up a bit more with images etc if anyone shows interest.
 
BTW yes you can use it at HF just the frequencies you start/stop on the scan HAVE to complete before you move. So be realistic if you are mobile driving.
 
 

Tuesday, 5 September 2017

4SQ why homebrew you can buy all the bits :-)

One email was interesting.... I'll not reveal the sender.

In essence they asked... 4SQ why suggest anyone homebrew you can buy all the bits :-) I guess you can for a price. So lets just take this as an example... probably one of the more 'popular' hybrid controllers, this one even has a send the signal to all 4 a the same time option (expensive to add that bit I am sure!)

https://www.thedxshop.com/as-4sq-40-four-square-hybrid-controller-for-40m.html

£598.99   Inc VAT

The 75 ohm matching cables £ 420 Inc VAT

You then have the actual 4 GP verticals, coax feeder to the control box, a 12-14V power supply that will switch the relays.  Very very conservatively add another £600 Inc VAT

That gives you a system that will cost about c£1500

Amusing to say the least.

Ok it is capable of KW+ and no construction or figuring out required. Well not much anyway, use a tape measure to layout the antennas and then screw a few PL259/SO239 together.

I'm going to see what a homebrew system for 40 might actually cost for qrp fans. Decent enclosures, so IP56 or better outside, powder coated Ali for the shack, masts and all cables and connectors included and pre-measured as an option as well. I will probably do the same for one using KW capable parts for those DX trips, and another for UK home and club use 100W/400W. I wonder if anyone would be interested? Contact me if you are as would be interesting to see what the interest is.

Might even see about using a 5th element as per the NCJ article a while back.