Logged in users > User Diaries
My other hobby, ham radio
ChrisOlson:
We are enjoying nicer warmer weather in the Midwest here. So I took the opportunity yesterday to convert one of my elevated ground plane verticals into a 40m 1/4 wave
It works really good. The elevated ground plane verticals have just about zero ground losses compared to a ground-mount with in-ground radials. Provided you can come up with a suitable mounting system to hold a big antenna, they are pretty fun to play with. The antenna pictured has shortened ground plane radials, but it still tunes up fine on 40. It is built almost entirely of EMT conduit at a cost of about $22. The one on the other end of the shack has been converted to a 15m 5/8 wave, built specifically for the Pacific Maritime Mobile Service Net. The two antennas can operate simultaneously on two different HF bands with no problems with RF coupling, with the ground plane placed at slightly different heights.
This is the kind of stuff I enjoy in ham radio - building and experimenting.
madlabs:
Chris,
Nice looking vertical. Is that EMT conduit on the entire vertical part? What are the radials made of? They look quite rigid. How is it fed?
On the ham front here, the YL and I finished up the Softrock SDR kit and it works quite well! Very fun to build and both the YL and I learned a lot. Among other things that I need a new 'scope. We are going to buy the TX kit they sell and then see how many states we can work with it.
Jonathan
ChrisOlson:
LOL! That should be fun seeing how many states you can work with that SDR.
Yes, it is all made of EMT conduit except for the base. You can get that EMT for like $1.92 for a 10 foot section of 1/2". This is a photo of the base of the 40m antenna.
It has a base capacitor made of a piece of 1 1/4" Schedule 40 pipe 9" long. I put two layers of big heat shrink tubing over the base of the vertical radiator and shunk them onto it for an insulator. Then that barely slides into the piece of pipe. And in the bottom of the pipe there is a piece of 1" Schedule 80 PVC tubing that keeps the vertical radiator from sliding in anymore, or shorting out. That piece of PVC is held by a self-tapping screw that goes thru the base and into the PVC. Then I expoxied the top of the vertical element in place with JB-Qwik Weld.
The base capacitor allows me to run a full 33 foot vertical radiator, as the VF of the EMT is about .92. The capacitor cancels the inductance of what would be otherwise be a too-long antenna due to VF in the tubing. So it resonates at 7100 kHz with a full 33 foot radiator. The radiator is made of 1" EMT (1.363" OD) at the base, telescoping up to 1/2" EMT at the top.
The ground plane radials are made of 1/2" EMT with a 3/8" flange nut welded into the end of the tube. There is three 3/8" bolts welded to the 1 1/4" pipe and the ground plane radials screw onto those bolts. They are 10 feet long.
The ring is a shunt transformer that goes from the grounded part of the antenna to the vertical radiator, so the vertical radiator is also DC grounded. By selecting a tap point on the ring, it transforms the impedance to match your feeder. I am feeding it with RG-6 TV coax, 75 ohm. Then I use a 1/12th wavelength section of RG-8 on each end of the RG-6 as transformer matching sections to make the 75 ohm "look" like 50 ohm at both the antenna and transmitter. It tuned 1:1 VSWR at 7100 KHz and is useable without the tuner from 7000-7200 KHz before SWR goes over 1.5. Using the amplifier with tube finals I can run the entire 40m band with it without using the tuner by changing the loading on the amplifier. The amp doesn't care about 3:1 VSWR as long you load and dip it so the finals are happy.
It is way stronger than any aluminum antenna, but it is somewhat heavier. All the telescoped sections of EMT in the vertical radiator are screwed with self-tapping stainless steel screws so the electrical connection between the pieces of the element will never go bad with age.
ChrisOlson:
BTW mad, if you or Mary want to try that 40m vertical out, tune in on 7091.3 signal center with PSK63. It's on that just about 24/7 and I got a QRP beacon that comes out once an hour at 2 watts. I try to keep the beacon as close to the top of the hour as possible, but I see the last one just went out at 0113Z here. If I'm not in the shack you can leave a screen message with Fldigi, or whatever with PSK63 if you see my beacon on there.
For Mary, it would probably be better on 40m during the day on NVIS. For Mad it would be at night when 40 is propagating.
madlabs:
Chris,
Many thanks for the detailed information on your antenna build! I might have room up on a shipping container but my solar panels would be within oh sh...oot range. I see you have some panels that look like they might be in range. I am interested in antenna with radials, my soil is really bad.
At work for 48 hours but I'll listen for the beacon when I get home. Where is your qth again?
Jonathan
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version