HB9CV Antenna

I have an S9 noise level on 40 and 80 Metres. It seems to start dropping off near 30 Metres and has disappeared at 20 Metres. It appears to be electrical in nature, as a constant buzz. The source is very local, I am sure. Anyway I wanted to try and DF the source so I did some googling to find out what others use/do. I found some very good resources for tracking RFI. ON4WW has a very good resource and some tips.

From what I found, it appeared a hand held HB9CV 2 element 2M beam might be a good option to couple to my FT-817 and go walkabout of the area to try and track the source of the RFI on 40 meters.

I found a couple of very good sites on how to build a HB9CV for 2M and worked out what I needed.

So I had a look around my "junk" and found that I had everything on hand, and with a beautiful Autumn day in progress, I set to work.

This particular antenna needs a capacitance in series at the feed point, and 9A7PJT (Update: Unfortunately the PA7PJT website no longer exists. Wish I had copied the page.) had a good description of using a 50 ohm coax stub, rather than a variable capacitor, so I elected to use a stub. This worked very well for tuning the antenna by snipping off about half a centimetre of the stub until the SWR was "1 to 1". I say that as I got it to the point the needle didn't move on 146.500 and I got full power output from the FT-817 so I figured it was close enough to tuned and resonant. 

Testing showed it to work very well. I fired it into a local repeater and got full scale on the bar graph on the radio pointing at it. So it had forward gain as the vertical always got a couple of bars less. Pointing it in the opposite direction, the bar graph dropped to about 3 bars, so it's got good Front to Back ratio. It also has some good side lobe nulls, so all in all it works very well. I am really happy with it.

I could also trigger distant repeaters that I couldn't with the vertical antenna.

Only problem I found was that it is so well tuned on 2 Metres that it didn't pick up the HF noise I was trying to DF in the first place. HI!. (In the end I used an AM transistor radio to find the noise source. It was coming from an old industrial shed about 500m away that appeared to have electric motors running all of the time. Update: have moved from that location so no longer an issue.)

Anyway, I have a pretty good 2M portable / fox hunt beam antenna now.

73

Cambo

The full beam. 

The boom after the reflector doesn't affect it so I made it long enough to hold. With only 5 watts, I dont have to worry about insulation, although I will put a handle on it for comfort.

Both elements are driven. This shows the phasing arrangement. The coax stub can be seen mounted on the top side of the boom. The feed coax is mounted underneath.

Testing the home brew hb9cv antenna with a Yaesu  VX-170 handheld.