Monday, 25 July 2016

Cook Islands

Ok will be going, E51KTA I can confirm that now.

BERU 2017 (Middle w/e in March) w/e so in contest BERU ONLY outside will also be looking at WARC bands.

I'll confirm exact dates in time as suspect couple days before hand and the week after.

Tuesday, 19 July 2016

TRX & SDR Switch

I have one, but never seemed to have gotten the ELAD switch to work with SDR RX so will look at this again.

I'm off to EU-011 for IOTA and I know that sometimes it might be good to use an SDR RX to monitor either same or different band for activity. But it is important when TX you connect the SDR input to ground.

The easiest way and an initial scribble (image should follow) suggests the SDR RX RF signal should pass through the antenna relay, this is either switched by the transceiver PTT output to ground, and RF sensed or manually.

It will be important that this is both fast enough to protect the SDR RX and does not cause any relay chatter. Obviously the relay between the SDR RX should be NC and it is switched to OPEN on TRX/PTT.

I suspect 2N7000 or 2N3904 might be used to switch the relay.

The RF sense, the circuit I have from the miniboots PA worked FB so will probably try to reuse that. Alternate might be from

RF from the transceiver should be rectified with some current limiting. The resulting DC voltage turns on a simple NPN transistor or FET. A switch would have the same effect. The turn on of this device flips a relay so changes the antenna input over to ground. The PTT input should  switch in the same way.

I seem to recall it is a good idea (probably stolen for a transverter design) to include some kind of protection to the RX line so a pair of back to back diodes should be placed just after the relay to ground to protect the SDR front end from static or induced current as a result of TX/Operation.

The TX RF will NOT be going through this part so I suspect will need to have a sense circuit added to the TX feeder.

Tuesday, 12 July 2016

SDR and 4K HD TV

Got into work (sadly I am a salary slave for now) to find they gave me a new monitor and PC for my database stuff as well as the usual multiple monitors for the desktop, just so my DB views do not appear on the sys admins monitor.... It's a cheap Cello 42" 4K HDTV, one of these...


I tried a quick setup with an SDRPlay and SDR-Radio and seems to work fine (resolution is about Horz 3.5k x something suitably nuts) so going to be fun watching pile ups, before people turned up at work this morning. Thinking about getting one for home shack.... as £300 seems too cheap not to.

I don't care about the audio or the free view TV and it seems to work fine. Seems like got later HDMI as both 30 and 60 Hz refresh rates fine and do not see any obvious lag, the video card is some on board intel thing (cheap HP desktop).

I wonder if anyone  used one of these things as a monitor for SDR and got any comments?

Making antenna and cable assemblies for EU-011 trip

Finding wire I forgot (almost) I ever had.

GP's for 10, 15, 20 and 80m and 4 for 40m.

Will use 3 raised radials for all (except the 80m which will be ground radials) they will double up as guys as well.

Utilising pieces of Tesco chopping board cut with a circular hole and holes for the radiator and guys. The ground in the winter cow field should be fine. Must remember gloves for the thistles and nettles!

Feeder will be the coax I picked up from SM7UCZ a while back, I'll be qrp with the KX3 (+ spare) but it is low loss and good to 160W. Sold loads at Foxton rally but plenty spare (300m!), the three long lengths with RCA ends from the last EU-138 Utlangan IOTA contest trip should be fine for use.

The 4 square 90 degree phase shift I'll make a new one as last was for 17m. The controller should be fine for re-use. The 75ohm coax for the 1/4 wave feeds I'll remeasure the velocity factor and make those up a bit later.

Got to remember to take a great circle map and compass with me so that can align the 4 sq so that the predominant direction will be the UK.

Donated garden flex will swap for a double rubber socket and that should power the station.

The 6m quad loop from M1BXF will have use outside the contest. I also found my long lengths of CAT5 for the internet dongle (if I use it).

I expect will take 12V cell and wall wart for 6m /p, other island activiations.

Saturday, 9 July 2016

Coax for 1296MHz filter

Just picked up some coax (12ohm) from G4BAO to build a derivative of the 5 pole W1GHZ filter in an altoid tin for 1296MHz. Aiming (some hope on first attempt!) to tune for a centre at 1296.2MHz.

I'll probably use female SMA though.

Thursday, 7 July 2016

Planning next trip

Met up with and took Andy E51AND along to camb-hams/Cambridge Repeater Group meeting in Whitehorse Pub, Barton.

Tuesday, 5 July 2016

1296MHz filter

Going to TRY and make one of these for my bodging to build a DUC/DDC 23cm to SDR rig. I have a problem creating harmonics from the mixing products of the Si570 that I have used to create the 23cm TRX.

From W1GHZ design, from here, of course it uses an Altoid tin so that HAS to be good to start with :-)

The dimensions are a tad precise.

"Resonators are 21.2 mm center to center. Coupling rods are 8.8 mm
center to center from outside resonators."

Good job I have an accurate digital caliper.