A Vertical Dipole for 15m

Sometimes a simple construction project can be fun, I mean you cannot always be knee deep in solder, resistors and capacitors. Sometimes you find a need that needs fulfilling even if its just a boring antenna.

Next weekend (At time of this post) I am partaking in a WWFF VKFF mass activation weekend and working dx is going to be a big part of my strategy for the 8 parks i will be activating over 3 days. So i thought lets go vertical and lets make it a dipole so there are no stupid radials and counterpoises to contend with.

I wont boor you with formulas and measurements, i am pretty sure you all know how to google a frequency length calculator to make a dipole, but rather just to show you how i went about making this and the results i achieved.

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I constructed a T out of some old conduit i had laying about, this is to get the feedline coming off at 90 deg to the antenna for 500mm.

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The feedline should come off the T at a 45deg angle to the antenna, i do not have the room to do that at home, this results in a narrower bandwidth for the band in use.

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The antenna was a little long 5cm in fact. it has since been trimmed and is now swr of 1.5 or less across all of 15m

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The ultimate test is what it does on the air. A quick test on Reverse Beacon network showed that i was being heard in places on this antenna up to 10db snr higher than the 40m dipole i use at home. And for those China stations, it meant being heard rather than not being heard. All in all i am happy with how things have turned out and i look forward to getting this baby in the air next friday and working some DX.

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Echolink on Linux

As you likely already know, the Echolink team do not provide a native linux solution. The best they offer is run it under wine. And if you run a modern linux distro that is up to date, and have tried to install echolink under wine, you will know that it crashes before the unpacker has done its job. But, fear not there is a solution.

sm0svx has written a native linux Echolink client and server and it can be found at https://github.com/sm0svx/svxlink . Now this is not going to be an easy sudo apt-get install, you will have to compile from source and it has a string of dependencies that also need to be accounted for before you do anything.

I run Linux Mint, but these instructions should work for any debian/ubuntu based distro. For others replace apt-get with your package manager commands. Yum on redhat/centos for example.

 

Step 1: Install all the dependencies:

Step 2: Download the source files:

Step 3: Unpack source and issue the following commands:

Sit back and wait while the software compiles:

Step 4: Run the Software:

And that is it really, you can make install if you want, but i generally run software like this locally from my home directory. QTEL is the echolink client software and svxlink is the server client. Hope this helps,

 

Enjoy.

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40m Direct Conversion Receiver

 

 

My home brew cw station will consist of 3 parts, the receiver, the transmitter and the tuner. Each will be built separate of the others and brought together at the end as a whole and hopefully it works. The receiver will be direct conversion using parts of the schematic from Experimental Methods in RD Design by Hayward Et Al. The parts of that i will use are the preamp front end, the audio diplexer and LNA preamp and the headphone amplifier. The mixer will be an ADE-1 from Mini Circuits rather than a TUFF-1, the audio filters will be active OP Amp Salen Key types and the VFO will be an Arduino DDS VFO as you just cannot beat them for stability and easy of use and rather than headphones, the headphone amp will be use as a preamp to a conventional audio amplifier driving a 4ohm speaker.

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IMG 1: Schematic from Experimental Methods in RD Design by Hayward Et A

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IMG 2: Front view of the case

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IMG 3: Arduino nano on etched board with DDS and TX RX switching relay.

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10w Class A IRF510 Amp

So I like to learn by doing, and it was time to learn about amps, biasing, mosfets and all other things, I thought what better way to learn than by building something and hopefully not ending up with Einstein hair or the house burning down.

I did a scour of the web and found a ton of schematics all pretty similar, claiming anywhere from 5w out to 30w out from a pair of IRF510 Mosfets. So far i have managed to get 10w out of a pair, which is the biggest amp i have build thus far in my limited time in radio and electronic construction.

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This is the schematic I used, yes i drew it up in LTSpice and did some simulations and no for those wise people that bias network wont work like that in Spice, I just used a voltage source connected to the 22ohm resistor for that.

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This is the amp as constructed with scope and signal source connected.

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10w out on the power meter, would be nice to claim 100w HIHI.

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Its pulling a little current, I will be playing with the bias to bring that back to say 1.5a, its happy and stable there, no thermal run aways or anything, but as you will see there is slight distortion on the wave form.

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A slight bit of distortion, that i will clean up with bias.

The next things to learn about are temperature compensated bias just so it does not run away and explode and some feedback to help with IMD etc. I have had a heap of fun with this little project and have learned a lot, still a long way to go, to get to the 20w I am aiming for, and i doubt that i will get close to that figure with this amp, but, its a step in the right direction and 10w is the biggest i have achieved so far,

Cheers,

Rob.

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