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Using cheap ferrite beads for an LFA choke

The contest club I am part of uses 2M Loop Fed Array (LFA) yagis for their QRO station. It’s always been advised to use a choke of some sort as close to the feed point as possible to prevent stray RF traveling back down the outer of the coax and into the station. The cheapest way of doing this is by creating a coax choke using 2 to 3 turns of coax around 2″ in diameter but this is also quite messy and risks fracturing the center conductor or foil in the feeder.

There are several commercial ferrite chokes available which replace the messy coax choke and one of our members has a large stock of unknown mix ferrite beads (which can be purchased in a pack of 5 for under £2) so we decided to test how well the unknown mix ferrites worked. Continue reading “Using cheap ferrite beads for an LFA choke”

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External GPS for TM-D710

I’ve been running my TM-D710 in the car for a while using a Garmin GPSMap 60CSX which works well but does add clutter to the dashboard and is just another device to remove when leaving the car in a public place. I could upgrade to the newer TM-D710G but I can’t justify the £550 price tag just to get a built in gps so I have decided to add a gps unit to my existing unit.
Continue reading “External GPS for TM-D710”

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Diamond X-300 repair

I did this repair many years ago after the mounting failed on the X-300 (original single bold stub mast) which allowed the antenna to sway. It gave a few more years of service after the repair and mounting modification and was only taken down to be replaced with a new X-510 which has the same mounting modification.

The X-510 has been up for many years with no issues despite being battered by the winds and salt coming off the North Sea.
Continue reading “Diamond X-300 repair”

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T2FD Calculator

I love a good T2FD antenna and have built a good few. There’s a few variations but they all work well and are easy to construct. I’ve been asked a few time about the length and spacing so I made a small Excel sheet to work it all out and provide data for the 3 most popular variations.

Free free to download and use. The sheet is protected to prevent the formulas from getting messed up but if you would like to experiment with alternative formulas then please just contact me for the password. All I require is for my original credit to remain on any derivative works.

M0LMK T2FD Calculator

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4:1 BalUn

I’ve been wanting to built a good 4:1 BalUn as part of the never ending project that is my HF antenna system for some time and today, I finally got around to the job. This is a “true” 4:1 Current BalUn that is wound as two separate 1:1 current baluns and then placed together to create the 4:1 ration. Any 4:1 built on a single core that claims to be a current BalUn is lying and is actually a Voltage BalUn! Continue reading “4:1 BalUn”

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Ladder Line Surge Suppressor

I usually get static build up on my HF doublet due to sand particles (I live above the beach) in the air so have been thinking about a way to bleed off the static and provide some protection to my TS-590SG. After a little research, I came up with this, a lightning arrestor/static bleed device that provides a permanent path to earth for DC whilst allowing RF to pass and providing protection from nearby lightning strikes. Continue reading “Ladder Line Surge Suppressor”

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1:1 BALUN for ladder line

I needed a 1:1 balun to use with my home brew doublet but I needed it to go between the ladder line and the SGC-230 tuner so it needs to have stud terminals on both the input and the output. I took a look around and decided that making one was the best option.

It’s made using 11 turns of figure 8 twin lead on two stacked FT240-43 cores. See the pictures below…

Continue reading “1:1 BALUN for ladder line”

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Simple APRS Transmitter

I started to work on a simple APRS transmitter today so that I could use it as a antenna test bed for Project Swift.

It was very simple to build using only an Arduino Uno, a Venus GPS receiver a Radiometrix HX1 module (on 144.800Mhz) and an SMA PCB socket.

The completed board looks like this…

After playing around all day with the APRS message format, I managed to get it working and updating to aprs.fi via my own igate.

Next up will be a test with it installed in the car.

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NTX2 TX blip

I finally managed to get the NTX2 and GPS working together thanks in no small part to NigeyS and fsphil from UKHAS.

One small problem still is that the RTTY signal from the NTX2 has a small “blip” in it that destroys the string. This must be an issue with my code somewhere as I can run some demo strings through the NTX2 using some simple code with no problems.

See the blip? Not sure what is causing it but I guess I better find out!

Update……

All fixed.

The blip was due to a drop in voltage. The GPS was drawing more current than the power source could supply. Plugging in a 1A 12V PSU fixed the issue.

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Arduino at the ready

I will be using a Arduino the base building block of project HABAT.

The fact that is is mall, inexpensive and easy to work with are the main reasons that I chose the Arduino. There is also a large community of users who I hope to be able to turn to when I need help!

This Arduino will form the base of the tracking transmitter that I will be building to test HABAT.

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Breaking it down

So lets get project HABAT off to a start.

Like any good project, I need to break this one down into bite sized chunks. Here is what I have come up with:

Aim: To create a automated platform capable of receiving the balloons GPS coordinates, performing the necessary calculations to determine the balloons position relative to itself and then actuating a pan and tilt platform to aim a high gain yagi antenna at the balloon.

Sounds simple huh?
Continue reading “Breaking it down”

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Simple stacked J-pole for 2M & 70cm

Following the death of my cheap fibreglass tri-band collinear, I decided to have a go at constructing a simple dual band antenna for use at home.

I was looking for something that was vertical, omnidirectional and with good gain that I could make quickly and easily. The answer came from Sean, M3FVB in the form of his excellent article on building a 8db collinear.

Continue reading “Simple stacked J-pole for 2M & 70cm”