Saturday, September 06, 2008

The QFH (Quadrifilar Helix) antenna

...Another day, another antenna.
For an long time I was wanting to receive weather images from satellites but lack of time had placed in standby my desire.

After getting the first images with the Kenwood TM-D700 it was time to get an dedicated receiver. Checking the available options including building one I opted buying one from Miroslav (OK2UGS) at his website
"Miro" was at the Ham fair in Germany so it took some more time to send me the receiver but as an compensation he sent me one pcb board for an DRM receiver (I have now another project in standby, hi)
After completion of the receiver (was a matter of putting it on an box, it come allready built).

I decided to make some tests with different antenna designs I saw at the web. Soom I arrived the conclusion the for the right job the right tool so on to make an QFH antenna.
The best (best relation between instructions/cost/easiness of construction) design I saw was the one at: although for a total understanding of connections the schema at is more clear (he has an nice use for some ready available materials, hi)

The antenna was build with ready available materials ;electricity tube VD16 and VD32, RG58 cable and electrical isolation tape and some more self amalgam tape. Total cost was around 15 Eur I think, excluding my time :)
The dimensions you can get from the above sites and the images are bellow.
I am quite satisfied with the image quality but still trying to improve. I use wxtoming software running in Linux. Please read the wxtoimg FAQ if you are not getting nice quality (I had some problems by not reading the FAQ).
At the moment I am putting the images received at:

The antenna during build process.

Some measurement:

And this is my "radio" horizon from South (left side of image) to North (right side of image).

73 de CT2GQV

p.s. Are you an English native? Probably you can correct my lousy English, we are allways learning so all comments are welcome!

Sunday, July 20, 2008

The SWR meter (one of)

After making the SWR meter for the antenna tuner I am building I decided to finish another one that I never put to work due the low acuracy.
It was based on an design I saw on the net but works lousy for the low bands so i decided to use the box and some internal parts and build a new swr meter based on this design. My design isn't exactly the same except the main parts (torroids and basic schematic), my microamp meter connects directly to the REF/FWD switch and I also bypassed the choke coils.

Here is another view:

Monday, July 07, 2008

First APT weather satellite image!

I am waiting for an dedicated weather satellite receiver, meanwhile I decide to test the waters with the trusty TM-D700 and one of the home made vhf vertical antenna.
After installing the software (wxtoimg) in the dedicated to radio Linux computer (I only use Linux) and after updating the keppler elements the next satellite pass was in an hour, so nothing like wait for the transmission (I still remember the first time I listened to an amateur satellite).

Honestly I was expecting an worst image due to the antenna/radio setup.

Here is the antenna (you can call it any other thing) and the first image:

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.

Thursday, May 22, 2008

100 W dummy load

Some time ago I needed an 100 w dummy load for of air transmitter testing (it's bad to put 100 w on an antenna and whistle ).
What beter use for 42, 2k1 (2100 ohm) resistors in parallel :)
The box was done with an paint container after some cleaning. Originaly the idea was to put engine oil inside for termal dissipation but if I don't transmit for more than an minute theres no overheating problem.
The resistors were placed in an PCB board all lined up and the other end conected by an wire mesh.
The photos show the final product.

Sunday, May 11, 2008

Dummy load for bench testing

Another use for the mints box!

Some time ago I made some dummy loads for testing transmiters on the bench. For full power transeiver testing I have another one of 100 W also homebrew.
The loads were made using some recycled boxes and carbon resistors for not adding inductance in the circuit.
The small one is for UHF and was made out of SMD resistors ( 2 of 25 Ohm in series ) the other just for VHF is made of 4 resistors of 200 Ohm in paralel. It has an 50 Ohm resistor near the load connected to an RCA plug so I can transmit on the dummy load and get some signal without afecting the testing circuit.

There not much to say about this litle peaces, just drill some holes, put the plugs and solder the resitors, but if you have any question...just don't ask :)

Saturday, May 10, 2008

Speaker box ( first sound)


After some spray painting (not an great job, but hey, I'm not a painter!) it was just an mater of placing the drivers in the box and make the connections.

After inital tests with the FT-102 and FT-307 I think it just needs an litle bit of tuning, first will make biger holes in the box, the sound it's an litle on the treble side. I think it will sound also better if I close the back of the box. Anyhow the sound is bright and on an fast test on 40m with lot's of noise I could copy lot's of stations, the FT-102 helps a lot on this.
The two speaker on top are 5.1 speaker from an old stereo that are being used for the TM-D700 VHF/UHF.

Detailed costs:

speakers: 24 Eur (more or less)
Bolts: 3 Eur ( a litle bit less )
Plugs (jacks): 4 Eur

Paint (left overs)
Wood (left overs)
Tools to make the round holes: 12 Eur (will use on another projects).
Cable (left overs)
My time ( priceless )

So the total cost was the same that would cost only one small CB speaker .
There's no excuse for not building at least one speaker box for your ham station! Not to mention all your antennas... later on this subject!

Sunday, May 04, 2008

Speaker box

After two sucessfull loudspeaker box for my home stereo I decided to create one to my radios.
Bought three small speakers just like the one used on television sets, just because they have good sound for voice.
Had some small peaces of wood laying around and created an small box, I'm not an great carpenter by I think after some painting the box will be nice looking.
I could use only one speaker but the wook size was ok for three and I have more than 3 radios so I still will have to build another speaker box.
Why do I have the trouble to build this box, well, just because I can and I think speaker boxes are overpriced. Each of the speakers only cost less than 8 Eur and the box nothing. The sound quality is not that important on radio communications, antennas are more important. So you can have nice sound for half the price of an miserable brand speaker.
The prototype:

Still need to drill the holes for the speakers and do some painting. After conclusion will post the pictures and an audio report.
Here the other side around:

This box will be for the Yaesu FT-102, Sommerkamp FT-307 and Kenwood TS-50. For my VHF/UHF dual bander I used an pair of satelite speaker that come with and stereo system.

Thursday, February 07, 2008

1 Year later

After one year without doing nothing except cleaning some dust, i think I will get on with the construction.
Must review all the connections and align. The easy part (soldering) is done.
Meanwhile I bought an Yaesu FT-102 for restauration (I works but needs some relay cleaning).

Also in the process of building ans SWR/Antena switch/Transceiver switch/antenna tuner). Box is done only the antenna tuner needs to be done... lacking variable capacitors, probably will homebrew some.