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Friday 28 May 2010

K1 build.

40m Pre-Mix Oscillator Signal Spectrum and Plot
Pin 4 J6 Filter board

20m Pre-Mix Oscillator Signal Spectrum and Plot
Pin 4 J6 Filter board

Adjust the pre-mix filter using an oscilloscope and pin 6 on J6 filter board.
(nice thing is same pin both bands) You realy need 4 hands to video this so apologies poor video.

A signal at last!

Tuesday 25 May 2010

PIC-A-STAR group photo

Made it to a group photo and chat this year.

I'm the tall one in the middle of the May 2010 - Luton car boot sale (Dunstable Downs Rally) photo.

Saturday 22 May 2010

K1 build RF part II

90% of TX side done now, just got the PA transistors and the transformers to solder in (just in place mechanically for now) and then that should be it as far as melting solder is concerned. There was one missing 473 (0.047uF) cap (C50) I have substituted in something from my own supplies that should work until Elecraft send a replacement.

The alignment for RX doesn't always seem to work for TX and the manual and notes say that the K1 uses the same filters for RX and TX and the uPC in it does a calculation and the ALC sets output power to less than 0.1watts

Anyway should be done soon. I am off to the Dunstable Downs rally tomorrow. Hope to be able to finish the build over the bank holiday.

K1 build. Up to RF board Part I

Just finished the build of the K1 up to the end of the RF Board Part 1.

Short video of the finished article.

The current draw with the back light is 64mA.

RX side all done and aligned. I used three signal sources, an FT817, a USB Si570 and a Colpitts Crystal oscillator using 2N3904 and 7.040MHz and 14.060 MHz so should be pretty true but the frequency can be amended through the menus. But once amended for 40m automatically the signal frequency for 20m was correct.

I have done the alignment with a side tone at 600Hz feeding the signals into a PC and used adjusted with an audio scope, built with stereo audio and the side tone is working fine and both hand and paddle key work fine. I have left keyer at 16wpm for now.

I might have to adjust the menu for S meter readings that suit later as I have left the level at L50 which is the default. I was listening to a cw contest and some of the local stations were definitely S9 and appeared so but the weaker ones did not seem to move the S meter. AGC is audio derived so an s9+40 signal causes a 'blip' and the AGC attacks hard the AGC decays pretty slowly. Turn it off and no S meter.

About to get the TX side started.

Wednesday 19 May 2010

SR V6.3 build

I found this an interesting read.

Monday 10 May 2010

SDR list

For those wanting to see a pretty comprehensive list of SDR options as they stand today then this link is seriously worth following:

Friday 7 May 2010

ARCI 72 part challange - realised error

Morning after... over the shreddies and visual check I realised as I had swapped FET from BS170 to 2N7000 having run out of one TO92 version (see for the two TO92 pin configurations) obvious error... I had connected one of the FET switches for mute backwards at the LPF input (shared with RX as forms half the BPF), anyway on TX instead of the FET passing RF to the LPF instead I was feeding the RF directly into the RX chain (abt 4W). Oops! I hit the key for a second and seeing no RF out and a brief squeak/squeal from AF stopped and heard no RX afterwards. Damage done but no magic smoke!. The IRF510 PA still seems to work so I have a TX :-) anyway might explain why it doesn't work ho hum! The 8 pin DIL PIC 16F629 (like old 509) was hosed as a result as the switch before the AF stage sent the RF into the PIC pin instead!

Normally a sensible builder would have reverse diodes etc in line and plenty of decoupling caps, voltage regulator, used npn transistor to switch the FET's and added an extra stage on the LPF as only 30dB down but omitted all this stuff to manage the part count! I realised I could have saved 3 as didn't need the xtal filter input transformer and couple caps used to decouple DC I had doubled up in two places (BFO and VFO into mixers).

Had this been a DC RX then 72 parts easy.... still learnt I could build a half decent <600Hz IF filter with two crystals not 4 or 5 :-)

Going to be interesting to see how the others actually managed it.

Thursday 6 May 2010

ARCI QRP 72 part challange - Going to miss it.

I am trying to get the project rebuilt/boxed after reworking the PTO. Unfortunately tonight after 3 hours trying I cannot get the cw RX/TX mute to function as it did and the TX has some nasty spurs so I've bust it somehow, and as not boxed up yet got to face reality I am not going to make the deadline to get this to FDIM so will not be entering. It is my own fault I mixed the Dayton and Friedrichshafen dates up so lost 5 weeks. Frustrated, angry and embarrassed all in one...

My one IC wasn't anywhere in the RF part I used PIC keyer that also controlled the RX mute (FET on the AF).

Anyway, when the w/e is over I'll write it up.

My final part counts were:

Basically a VXO FET oscillator using an IRF510 followed buy a 3 pole LPF. Some pulling possible using a small trimmer cap. Built for 80m.

BPF, that shared the TX LPF, FET mute of the front end and the AF section. DBM mixer, M5 Brass bolt PTO, 2 8MHz crystal c580Hz filter, 8MHz BFO (J310), RF amp/product detector (J310), AF amp (3 NPN).

PIC + one resistor. I would have added a side tone too but needed one more component!

72 total.

The whole lot could do with a bit more decoupling and as planned on battery use no main voltage regulation except one zener in PTO. I build every module on a separate PCB, manhatten/ugly style.

Tuesday 4 May 2010

What SDR kits are out there?

I was asked this at a rally demo recently:

>> I was talking to you at the Loch Erne (Enniskillen)Rally on the 11th April past.
I would like to know:
What SDR kits are out there to build
What would you recommend to start with and which one to work up too.
Where can I get them from and how much are they ?

> Any thing else that you think that I may need to know about kits and what software to use would be great.

The answer is going to take a while to formulate with all the information but this post will be a place holder for it.

I will fill out the sections below.

The initial starting places to look for information on building SDR kits could be: Robby has written extensive notes on the construction of all sorts of SDR kits. is Tony Parks website he is 'Mr Softrock SDR' as the kits are his. You can order directly from him but there can be some delays as he does the kitting personally.
There is an Elecktor SDR project, don't know much about it.
The Genesis SDR project is a bit more advanced that a softrock and for those who do not like surface mount the projects are good.
I have a kit in the design phase.

There are plenty of others out there I just either don't know them or haven't mentioned them,

All these so far use the concept of a PC sound card and software to decode the signals and the bandwidth is between 48khZ and 192kHz which is fine for most uses.

Expect to pay anything from £20 - £200 for an SDR kit. Any SDR TX options should NOT be considered by a beginner unless you have the RX side working first.

No matter what the RF hardware you need to run software for SDR. Don't expect to run it on that old 386DX DOS based system you use for VHF logging It will not work. You will need a good sound card and any reasonably modern PC should do well. The larger the monitor and the higher resolotion the easier you will find 'looking' for the signals. I use in shack an old Pentium 3GHz laptop or a Dual Core AMD 2.8GHZ laptop, 24bit 96kHz external USB sound card and twin 17" monitors. All together would cost less than an FT940 would. I do demos at rallies with an ASUS eeePC 4G which cost me £125 from Toy'r'us and the sound card in it is brilliant 24 bit and 96khz no problem and a 17" monitor.

Another option that Pat Hawker G3VA talked about maybe 10 or more years ago is to use direct digital conversion and digital up conversion to sample and convert RF directly to data and visa versa... the constructions are not really for anyone but the seriously experienced and surface mount components rule the day, go to and you will find some more details. They use FPGA chips to do most of the digital signal processing. Some of the newest FGPA chips have huge capabilities but cost £10K (HPSDR doesn't use the expensive end ones!) and those are what the military and broadcast radio and TV use.

Non kit options:
Flex Radio don't know much about them... very expensive!

Lots of options but a major one anyone has to make is are you going to try to run SDR with Linux or Windows.
Loads say they want Linux as it is open source and all that but and I make zero excuses for saying this but 99.99% of them never code a damned thing and much of what they say is hot air. The choice is really down to what you run your shack with, most use Windows and some of the more user friendly beginner software is Windows based. Not to say the Linux stuff isn't but it tends to be written for specific functionality not overall usablility.

No excuses for recommending it, as I am supporting Simon Brown HB9DRV (He wrote Ham Radio Deluxe) SDR-RADIO ( which he has now released v1.0 of. It doesn't have TX support and a few other things just yet but it will and if you know HDR and DM780 it will integrate with those nicely.

Other options are: (Again all Windows and no source code available)

A homebrew siggen I would advise anyone to try to look at building to look at image rejection is this

... I'll add to this as time goes on....

Monday 3 May 2010

ARCI QRP 72 part challange - Update

Further to my tests ages ago with PTO...

Here I am again with the same test rig but with a different construction technique. Again I post the information here incase others are interested in trying out a PTO.

I have fused a number of M5 nylon nuts together, super glued them and wound red electrical tape about them. Into this I can turn a M5 brass bolt. It is much more stable than the previous constructions. Anyway onto this I close wound about 45 turns (I didn't count them at this stage) of 28SWG enamelled wire.

Final construction of the coil and screw will involve moving this to the PCB and not being panel mounted. A second nylon bolt will hold the far end of the assembly 'true' with the brass bolt.

Then using the same setup as before I retested.

I can now get the PTO to operate between 4.673MHz and 4.3MHz which is perfect for an 8MHZ IF and 80m rig.

Anyway as this is a buffered PTO, needed a little lift in LO signal for the DBM but it added a couple more components to the count so will see how my rig turns out.

I'm not going to use any component that is not generally available and every one must be possible to obtain from the 'usual' suppliers.

Hope mine is going over to Dayton with a UK attendee.
My TX uses just 13 components, crystal controlled and there is about 4-5khz ability to shift frequency using two extra components. That was the easy bit.
My RX... I am still tweaking it a bit so the count is not up to date but overall I am inside 72.
The rig should have a keyer (so an AVR or PIC is my one IC!) but if I don't get the code finished, it won't.

Some images of various bits follow, it is my intention to build this manhatten/ugly style so no fancy PCB required.
The minimal component count crystal filter. "So how did I select the components to use"... no fancy calculus... I looked in the junk box and then through what 1% caps do I have > 300pf and found three 560pF, three 390pf and three 680pf. So I plugged for the 560pf and built this crystal filter.

Then just to check how it performed I used my trusty MiniVNA in transmission mode and took a look.
Nice sharp filter. Note I added the FT37-43 transformers after I measured it at c24ohms so used trial and error and made 12T:8T transformers so the input and output are both 50 ohms.
In this image the transmission appears to be down 20db (it isn't!)

The TX side is dead simple to keep the part count right down. I went for an IRF510 which adds some legs rather than a 2N3866 et al but this means /P use may be a little reduced.
The variable capacitor, series inductor and crystal are missing from this image but everything else is on the board. RF out is the white lead to left, key (basically short to ground) is the purple lead on right. The LPF is very simple just one half of a normal LPF to keep the part count down and I played about with values to get this to a reasonable level but seems to work, it is a single T50-2 and two 1000pf polystyrene caps as the oscillator is crystal controlled I did not see any spurs. I might grab an image of the spectrum plot and the LPF transmission graph and post them too.
Oh BTW don't copy the TX layout the above will not work, was an early version I took a photo of.

I went for a simple double balanced mixer. The two 0.1uF caps and 56 ohm resistor on bottom left is the AF output and they act as a RC filter. BFO in is top right, RF top left.
*** more to follow....

Sunday 2 May 2010

SDR/QRP talk at Cambridge and District ARC

Just been asked to give a SDR/QRP talk at Cambridge and District ARC.
As I am working in Cambridge again I expect to be local again for a while so this looks possible. No idea about dates yet.

I suspect a talk/demo might be best.

I'll have some of the Softrocks built with me and a handful of other qrp kits and builds.

K1 Build

Some photos here