“Old Mc-Lisa had a farm, ee-eye-ee-eye-oooh!“
Yet Another Antenna Project
As I have previously detailed, my 3rd floor apartment is pretty hard to ham from. I’ve hacked a few solutions that have allowed me to work about three bands so far, though I can only work two at a time due to space constraints.
It’s a bit of a pain in the neck to disconnect and haul in one antenna on it’s plank mount, so I can hang out another, or have to unscrew one hamstick from the mount just to swap bands.
I’d really like to spend more time operating on the air than constantly having to jimmy different rigs into place!
Antenna Farming for Small Spaces
With that concern in mind I’ve started work on another project– a “square foot antenna farm” of four hamstick mounts on one bracket, two closer to the building side by side, and two pushed another 6 inches further out.
My intention is to have four different hamsticks packed into a space that is about a foot square. I hope to have 40m, 30m, 20m, and 17m available at one time, though obviously only one will be transmitting at a time.
This creates new challenges–
- For example, the mounting board needs to be wider, and thus heavier
- The bracket hardware needed to hold four sockets are also heavier
- All antennas are sharing a common ground, which could create loops or parasitic interaction between antennas
- All of the above makes the whole assembly heavier to lift and place in the window
- Different length radials needed for each antenna
- Bigger mass of metal in the mounting hardware majorly changes the tuning of the antennas and may require a tuned counterpoise dropping down below the mount out the window.
So there’s a lot to work out.
Here are a few photos of the project in progress:
The hardware above is built using a pair of L-brackets and a pair of flat strap hardware extension pieces from Lowes, and a pair of Workman dual antenna mounts, bolted across the L brackets. Washers are used under the top bolts to give the mount a little tilt to allow the antenna whips to clear the roofline of the building.
I add the self-adhesive weather-stripping, which I get in rolls, to the vertical sides of the board to seal any gaps between the boards or the sliding window pane. It does a respectable job of forming around the jumper coax cables where they pass to the interior.
As the mounting plank gets heavier with all the extra brackets and 4 times as many antennas, the risk of dropping the whole thing out of the window increases, so I added a pair of “gate handles”, also purchased at Lowes to the back.
I’ve actually considered this for the previous, smaller mounts– sometimes they are awkward to move, or pry sideways in the window frames channel so I can take one of them back out of the window or check the cables. I had one incident where I did nearly lose my grip on one of the antennas while putting it out which gave me a little mini-heart attack!
But this mount is just so heavy it’s a necessity.
Because I have radials actually taped to the inside of the wall running around part of the room, I needed the radials to be easy to connect and disconnect quickly.
Anderson Power Pole connectors accomplish this nicely, and connect to the antennas via one of the mounting bolts for the L-brackets.
Note how the cables pass between the weatherstripping on the boards easily. I’ve pretty much abandoned the use of the MFJ-Feedthrough panel as this works fine.
The cables are shown wrapped a few times in snap-on ferrites that act as chokes, but I have since move them a little closer to the antenna feedpoints, and outside of the window instead of inside.
Taming the Tuning of 17m
I admit I’ve been taking a break from this project for a couple of weeks, partly because the prospect of having toe go around in circles for hours, tuning and re-tuning four different antennas, all interacting with each other is a bit daunting.
I initially took my well tuned 20m hamstick from the original mounting plank and put it on the new quad mount to see what I had. The SWR on that was just ridiculous– somewhere between 20:1 and infinite! Yiikes!
All that extra metal on the quad-bracket definitely changed where resonance lands. I threw up my hands and put it back on the old mount for a while. Ugh.
A friend suggested adding a hanging counterpoise wire of 10 or so feet right at the feedpoint of each antenna might allow tuning to a more acceptable SWR.
So after installing the 17m hamstick I have onto the mount tonight, and working with adjusting the whip length, and adjusting the radial length till I got as low SWR as I could, I attached a counterpoise wire to the nearest bolt on the mount and tossed it out the window.
I played with the length by rolling up and unrolling the wire at the free end for a while, and eventually got the SWR down to just under 2:1 for 17m.
I’m not sure I can get it much better, but tomorrow, I’ll see what the Icom 7300’s antenna tuner can do with the antenna as is.
Interestingly, the really narrow, sharp dip you normally see with a hamstick in the SWR scan is now a very broad, shallow curve across the whole band.
It remains to be seen whether that’s a good thing, or not, but I guess I get to find out in the morning!