40M Dipole

I recently got the Ham It Up Upconverter for my Nooelec SDR. All of my HF antennas are being used with my main transceiver; so, I decided to install a 40m Dipole. With my main transceiver, I am able to hear traffic on the 40m band day and night. This is the main reason I chose it as my first HF SDR antenna.

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All of my dipoles are setup as an inverted v. This helps save some space. Get the top of the v as high as possible. This antenna is cut for 7.150 MHz. To calculate a different frequency, you can recalculate the length in feet use the formula “Length feet = 468/frequency in MHz”. Divide the answer by 2 and this will be the length for each element of the dipole. An online calculator can also be used to calculate the length of the dipole.

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For this dipole, I wanted to try a 3d printed enclosure to house the junctions.

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A scrap piece of LMR-400 is being used at the feed point of the antenna.

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Each leg of the dipole is cut longer than needed. It is easier to trim the antenna while tuning than adding wire.

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The legs are connected to the LMR-400 using terminals. On the leg with the aluminum braid, Noalox was used to prevent corrosion. The terminals are torqued down tight as possible.

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Weather sealing putty was used on each penetration. Wire ties were installed as tight as possible on each conductor. This will act as strain relief. Weather sealing putty was also used around the edges to seal the top. Stainless steel screws secure the top.

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The extra length of the LMR-400 is coiled to form an air balun or air choke. The LMR-400 being used is pretty stiff and has a larger bend radius. Make sure each coil runs parallel to the next coil. This is not needed for my application; but, it does not hurt and allows me to use it as a transmit antenna in the future.

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