A New 40m Dipole

Up to this point, if I wanted to get on the air, I had three antenna options:

  1. Walk 20 minutes to the lake, spend 15 minutes getting a 40m inverted-V set up in a tree, and hope I didn’t forget anything. This has been netting me good results, but is a bit cumbersome.
  2. Set up the PHF40 loaded-dipole antenna on a tripod in the backyard. Also a bit cumbersome, and I’ve not had any success making a contact on that antenna yet. I suspect the efficiency is quite a bit down from a full size antenna.
  3. Try the random-wire I’ve got strung up around the office.

While it certainly doesn’t feel like it in the August heat, winter is surely coming. In order to ensure I won’t have a long operating hiatus once the snow hits and going outside is impossible, this week I set about putting up a 40m dipole in an inconspicuous place.

I won’t share exactly where the antenna is mounted, but suffice to say all parts of the antenna are about 12ft off the ground – much more of a skywarmer than a DX antenna, I should think.  I tuned this antenna the same way I did with my inverted-V, using just the MFJ-207 and a pair of snips.The antenna ended up being 31’6″ along each leg.

The final antenna is resonant around 7.075 Mhz with an SWR of 1.2:1 at that frequency, with a 2:1 SWR bandwidth of 6.9-7.240 Mhz.

Currently, the feedline is just a piece of RG-58 sneaking in through a window into the apartment. Interestingly, the SWR at resonance shoots up to 2:1 if I bring the metal window-frame down to within about an inch of it. I should note that I’m not using a balun with this dipole, just the usual center-conductor-to-one-wire, shield-to-the-other setup, so it doesn’t surprise me that the coax is coupling to the window. I’ll need to set up some kind of non-metallic passthrough to block airflow with maintaining the antenna characteristics.

After a couple evenings of listening, all signs point to this being a workable antenna! The map below shows the stations that I’ve heard (not contacted) in the past couple evenings. The station in red is one that I was able to contact, but we were fighting QSB and couldn’t really complete the QSO.

Hear you on the air!

73

Advertisements

2 thoughts on “A New 40m Dipole

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s