Sunday, June 22, 2008

PSK31 Interface III

After getting everything working with the PSK interface, it's time for an upgrade and to make a new one...
Just tried to make an audio transformer following the idea from DK1HTX in ,after searching the junk box for some enamel copper wire (none was found with the exact length and diameter) I decided to try with wire from CAT5 cable (Ethernet cable) and an toroid core from an old computer power supply, removed the old wire from the toroid and on we go with the cabling.
The result is not ok for every day use because there's no sufficient impedance in the wire but I am sure if you follow the instructions from DK1HX you will be successful! With my transformer you need to put an high audio level on the input to get some results but it's cheap to make this! Even buying the toroid and the wire it will be cheaper than an commercial transformer!
As soon as I have some time I will try this following instructions, I still need an isolation transformer for the weather satellite receiving....but that's another story!

Just did another audio transformer this time using thiner wire from and old power supply transformer and with 2m of wire, both input and output. Better results but still not perfect, will do still another test with even thiner wire 3 or 4m length.

Sunday, June 15, 2008

PSK31 Interface and Linux

After completion on this little interface (see previous post) I decided to test against my super Pentium III at 500Mhz Linux machine..... not super but it works :) It's an dedicate computer just for the radios.

First problem, I have Fedora Core 2 installed but didn't installed the development libraries so at the first attempt to compile the Gpsk31 software it failed, Installed the development and compiled gpsk31-0-4.2, had some problem compiling it and had to remove line 92 of menu.C (it was an menu option "about Gpsk", I think) no big deal, it's supposed that you know the software you are using.

After that verified that there was no sound on the computer and after checking the card in use ( dmesg | more ) and looked for audio string. I tried the following command: "modprobe snd-es18xx" bingo at first time! I have audio!
Dmesg output is this one:

"isapnp: Scanning for PnP cards...
isapnp: Card 'ESS ES1869 Plug and Play AudioDrive'
isapnp: 1 Plug & Play card detected total"

Remember, you have to edit some files to get audio every boot, will do that in about one year :) for now it's ok like this, I love to issue commands on the shell :)

Problems didn't ended on software, I was having problems getting the PTT interface to work, after checking that I had connected the cables wrong way on the 4N35 IC, I placed it "dead bug" on the air with the cables connecting directly and I counted the pins upside down (only in one of the sides).
After getting PTT to work it was time to get some receiving...
No matter how many circuits you made it's always special when some think that you build works!
I listened to some Spanish station QSOing with and Russian station, everything work like a charm.
I just didn't tested the audio on transmiting since Portugal is going to play against the Swiss team for Euro 2008 and I want to see the game :)

The finished product, can you see the 4N35 on this new technic? Dead bug on open air.

Tuesday, June 10, 2008

PSK31 Interface

Have long time ago made and RTTY interface but not even once using it, I decided to go for PSK31 now that propagation is not famous.
After searching the net for designs I decided to go for this one at

Having already bough one audio isolation transformer now I only needed another one (se the link at the end of the article to se the ones that DK1HTX did). I bought another one.
Searching the junk box box I decided to go for an perfume box. The holes for the led, potentiometer and cable were made by my trusty swiss army knife.

Doing the cabling and the connections I tried against my oscilloscope since the PTT part it's not done yet. I've got signal.
Now on to the photos!

Henrik (DK1HTX) also as an great interface at his home page he even home brew his own audio transformers!

The transformers I used were this ones (LTR-110) at around 12 Eur each:

Input (Audio ) connected to pin 1 and 3 and output at pin 6 and 8 of this transformer.

Sunday, June 01, 2008

VHF antenna (144Mhz), another one!

After building at least 4 different VHF and VHF/UHF antennas I found this design on the net and decided to build one to replace my trusty old one (little piece of TV antenna tubing and an support making an 1/4 wave vertical dipole).
The idea is to make an acceptable antenna at very low cost and weather/waterprof.

I started buying two plastic conduit tube of 3m each, so it will give me the opportunity to make two 1.5m antennas. Total cost was 2.5 Eur ( 1.25 Eur each antenna )

The aluminum foil I had in the kitchen and the electric tape and cable was in the spares box. So total cost by antenna could be around 4.25 Eur (and you still stay with lots of aluminum foil). 1 Euro to the PL plug, 1 Euro to the electric tape, 1 Euro to the cable and 1.25 for the plastic tube.
The tubes were VD12 for the foil suport and VD32 for the outside protection.
Now on to the images, it's self explanatory.

The aluminum foi was trimmed at the end to get the least SWR ( almost), I didn't care about getting to low because I would have to cut a litle more on the elements and since the antenna it's gonna be used to receive around 120 Mhz it's nice to be a little bigger.

Be prepared to do some trimming on the elements, put a little bit bigger and then cut with and knife in increments of 5mm till you get the resonance you want, my top element is around 56cm and the lower element is 39 cm.

The top cap will be placed latter, probably will use some plastic bottle inverted.
The idea is not to have an high gain but an simple and cheap construction that can last long in the roof.