Lessons at Terminal Velocity

The joy of failure is that I am forced to learn from my mistakes. It feels joyless now, but really it frees me from the burden of choosing to learn. Either I learn and improve, or I will no longer be burdened with finding joy.

Work began this weekend to implement a portable 40′ tower mast so I can raise inverted-V and vertical antenna elements out in the field with no other support structures around. I’ve seen it before, and I know it’s a viable option. I’m using army surplus camo netting poles (they come in fiberglass and aluminum), and some modular brackets that I picked up in previous hamfests.

With some measurements of overall mast height, 37-ish feet, and the anchors which are 30 feet out (roughly 80% of mast height), our buddy Pythagoras tells me the guy rope length should be 48-ish feet. So today I measured and cut 3 guy ropes, and marked their length by the foot, with orange safety ribbons every 5 feet. Attached them to rings and everything.

3 ropes from RGB D-rings attach to the modular brackets on top of mast. Pulley to the upper left. Moments before first raising.

But something was wrong with my measurements and math somewhere. The ropes had too much slack, so on the four attempts to raise the mast, I could not get them tight enough, even after shortening them by a foot each time.

Mast on ground, ready for first raising. Root pedestal at far end, near table.

On the 3rd attempt, the root of the mast came loose from its tent peg, the bottom bounced up, and I couldn’t get my right hand out from under the mast before it jammed into my thumb. Thankfully I had gloves and a hard hat, but it just wasn’t enough.

Crack in fiberglass top section, formed after 3rd drop.

Unfortunately, I destroyed a mast section on one of those drops. You don’t realize just how heavy 60 pounds of mast material is until it’s 40 feet up and falling to the earth at increasing speed. Crack.

And when you get 10 sections of it in the air, you realize just how wobbly and unwieldy it is, and just how dangerous the whole exercise is.

End of day, end of lesson.

After the fourth lift with a replacement section, I gave it up. Live to raise it another day.

I have some thinking and physical recovery to do. I need to build a pivot base to anchor the mast. I need to recalculate the guy rope length with all the brackets, rings, and rope stretch factor. I need to find another rope tensioner solution — these Mastrant-brand friction claws are sketchy and I’m not trusting them any further for my guy ropes. I need to either use a shorter mast, or plan and cut some guy ropes for halfway up the mast for stability.

And for the love of Marconi, I’m not doing this again without a helper. It was stupid doing this alone in the field, with nobody to hoist ropes or call safety.

Hard lessons. Back to the drawing board.

Vee

Experiments with operating the radio at home continue.

Had a wacky idea to use the anchor in the tree over my balcony as the support for a 20m inverted-V dipole, fed with 300ohm twinlead for multi-band matching. Brainstormed a plan to use a pair of bamboo fishing poles, anchored by pole brackets on the balcony railing, to spread the bottom ends of the dipoles apart and keep them out away from the building.

The signals I got were certainly louder than what I got on the Slinky dipole. Loud enough to hear buzzing and static crashes. I think the static pops were probably from the trees blowing in the wind. Had to experiment with using a mix of noise blanker, attenuator, and turning off the receiver preamp (IPO). At least the high-current area of the antenna, where most of the signal emanates, is at the apex of the V and right at the level of my roofline for better clearance to the East. So there’s that.

Heard 40m surprisingly well. Tried to match the transmitter on 40m, couldn’t get better than 5:1 SWR, so I swapped my DIY 1:1 balun with my DIY 9:1 un-un. The result? Better than 1.5:1. Yes. Even 20m matched OK, enough to trigger my desk lamp with 35W. Twinlead is good about taking up some of the impedance slush of a bad match and not losing much signal in the process, which accounts for how I could match on several bands.

Couldn’t get any QSOs, not even on FT8 (but that’s kinda crowded anyway). I’ll try again later.

This was a proof of concept from existing parts on hand before I wasted any time trying to “build it right” with new parts. It proved it worked better than expected. I guess I’m learning.

I do have some refinements planned:

  • Build a proper center insulator for balanced feed (instead of my repurposed Plexiglass insulator with unbalanced SO-239), with UV resistant plastic and weather protection for long-term installation and protection from wind/tree static
  • Cut a new 20m dipole and return this one back to the tote in the car
  • Build another 9:1 un-un or 1:1 balun for mounting outside next to the balcony door
  • Trim the twinlead for slightly longer than 20m resonance so the entire antenna system can match on 40m, and find a way to run it from the balun out to the apex without getting near metal objects or itself. It’s currently 40ft of way-too-long and is probably causing some matching problems on its own
  • Make better insulators and clips for the ends of the dipole to attach to the bamboo poles
  • Run the dipole legs through the trees without snagging on limbs, in an effort to get them at a more obtuse angle for better SWR and efficiency
  • Insulate the dipole ends (the high-voltage section) to prevent arcing to the trees
  • Fix the riggings and poles so I can deploy and stow in minutes without snags

Incremental improvements.

Balcony Into the Sky

Getting more brazen with my antenna projects at my apartment.

Used a reshaped coat hanger with a pulley and a lead weight to hook over a tree limb over my balcony. Now I have an anchor point to hang my 10m vertical dipole (or any other antenna that’ll fit). The anchor is below the peak of my apartment roof, so it’s deaf to the East for groundwave, but at least I can get out to anybody locally with decent towers at their QTH. Can’t wait for sunspots to kick up again for 10m to open up for DX, but that might be a while yet.

I also built this crazy, screwy-looking antenna.

Slinky Dipole, mounted and ready. Just add feedline. Radio not included.

It’s a Slinky Dipole, made from a pair of Slinky™ metal spring toys attached to a custom PVC center insulator and suspended with clothesline rope. I have it slung under the eve of my balcony for protection from rain since it’s not galvanized.

I used the length = 2πr * turns formula to calculate the actual uncoiled length and determined that it would resonate somewhere around 12.8MHz if completely straight. What I got was somewhere around 9.5MHz due to the induction of the coils lowering the resonance, as well as its proximity to the metal rain gutter and balcony railing. It’s electrically too short to resonate on 40m, so I tuned the antenna to 20m by clamping turns of the spring together with twist-ties to short them out. That got me close enough. I could probably dangle some wires from the ends or add another pair of springs to lower the resonance, but that’s another battle for another day.

Slinky Dipole, from the end, showing rope and mounts

Anyway, it’s a crappy antenna. It’s kinda deaf to real signals and picks up a ton of nearby noise, but it’s better than not having an antenna at all. I was kinda let down by how badly it performs, considering all the work I put into it, but heck, I did it and now I know.

The Slinky Dipole after completed construction.

I do have some improvement ideas, though. Maybe if I built a swing-arm assembly to move it out over the yard and away from the building. I could also try using a 1:1 balun to kill some of the common-mode interference, or just connect a 300Ω twinlead or 450Ω window line with a 4:1 balun to make it more broadband so that it almost always resonates with lower feedline losses. Speaking of, with my antenna tuner, I can get a resonant match on 40m, 20m, 30m, 10m, and sometimes 15m with 1.5:1 SWR or better. I’m surprised, even. However, 17m is 2.5:1 SWR, 80m is unmatchable, and 160m is almost dead silent.

Slinky Dipole, close-up feature of center insulator, bracket, and feedline attachment.

I’m going through the ARRL Antenna Book for inspiration. I wonder if I should make an inverted V and hang it from the tree hook, or if I should attempt something more grandiose like a triangle loop antenna from the hook or some kind of antenna-and-pulley system to ascend the arch of my roof. Who knows? I certainly don’t.

And I certainly don’t want to hear my landlord complain about it, that’s for sure. I haven’t paid an antenna deposit yet. Don’t want to hear it from my neighbors, either. But so far in the past week of operations, I haven’t heard a single knock on my door, but that’s not to say the neighbors aren’t getting interference. I have a desk lamp that gets brighter when it’s touched; when I key down and speak while pushing more than 40W, every voice peak causes the lamp to change state. So it’s a reminder to be kind.

BTW, I almost had a successful QSO with a station in Cuba on 40m the other night, running at 50W with FT-8 mode while using my Slinky dipole. Would’ve worked if my timing on FT-8 was right. Amazing, considering my balcony faces East and Cuba is due West-Southwest. Radio is funny sometimes.

Here’s hoping I can figure it all out, or at least enjoy the bumbling.

Blast and Blow

To catch you up to date: when I set my radio output to 100W full power in the car with the new mobile antenna, the SWR is so bad that the radio lowers its output power to 40W to save itself.

I experimented with a few hypothetical fixes:

  • Run on 12V battery instead of the car’s power system, in case the power system was actually not able to provide full current; no change. Power system is functional.
  • Disassemble antenna mount and scrape paint layers between adjoining parts for better conductivity; no change. DC conductivity is not the same as RF conductivity.
  • Adjust the ground strap and tighten connections; no change
  • Coil more feedline into 4″ turns as a poor-man’s feedline choke; no change
  • Clamp on a bigger ferrite choke outside the trunk lid and run more turns through it; no change
  • Run the feedline directly into a dummy load (a resistor with a heatsink); success at 100W. The antenna is to blame, and the radio is OK.
  • Insert my manual antenna tuner between the radio and antenna and adjust for best SWR: success at 100W

So, yeah, my initial assumption that I’ll need an automatic antenna tuner unit (ATU) holds up. The issue is that the antenna, the car underneath it, and the ground underneath the car together have the kind of reactance (impedance to alternating current due to inductance or capacitance instead of pure resistance) that causes more energy to get stored in the antenna system and then sent back down the line to the radio. The antenna tuner injects enough of the right kind of reactance to reduce feedback and make the radio happy.

Once I got the manual tuner set right, the radio was able to pump a full 100W on CW. Success. An automatic tuner will make that a breeze.

So tonight I was out and about on a drive. Pulled off the road to raise the antenna and make some tests and contacts on 40 meters. SWR was bad, so I inserted the manual tuner. Instead of digging into my radio box for the pushbutton I typically use to trigger the CW tone, I decided to flip over to FM modulation because, like CW, it has a 100% duty cycle (a solid signal to test power output). With a few keydowns resulting in low power output, I reached over to tweak the tuner knobs and get better SWR. Suddenly, the radio pumped out full power — for 4 seconds before it blinked off and died.

My initial concern was that the radio was fried, or worse, I had fried the custom power circuit I had installed, or even worse, I had killed my car and was stranded in BFE — none was the case, thankfully. The culprit was the 10A fuses I had installed in the inline fuse blocks (I designed the system for 25A fuses, but downgraded to 10A for paranoia reasons).

10A X 13.8V = 138W

138W is realistically more than my radio should consume, but there are losses inside the radio, voltage drops in the power line, and FM modulation spreads the signal out over a 3KHz bandwidth and consumes more power than CW signals.

So there you have it. I fried my first fuse.

Once I made it home in silent humility, I replaced the fuses with 15A units which should be able to take the heat and still be safe. I think that should be enough, but time will tell.

I learned a few things this week.

The Go Forward Backoff

Went to Belton, TX for the Ham Radio Expo held there twice a year. Big swapmeet and convention. Picked up a trunk-lip antenna mount for the car and a multiband antenna for HF — 80m through 2m. Cool thing about the antenna is that instead of using lossy traps to keep the antenna resonant for each band, it features jacks along the length so you can use the included jumper cable to manually select each band.

I took the new kit out yesterday for a test run, and unfortunately I’m not impressed. When connected to my antenna analyzer, the SWR on the antenna looks like it could go down to 1.25:1 after tweaking the length of the whip, but the moment I connect it to my radio and push 100W, the SWR gets so bad that my radio automatically backs off its power output to save itself. 40W is the limit, apparently.

My biggest suspicion is that the antenna mount isn’t fully grounded to the car frame. The frame is an essential part of the antenna system (it functions as the ground plane for the vertical antenna), and if it’s not properly connected, that RF energy goes back down the feedline and into the radio.

The mount has a rubber pad to protect the paint on the topside, and the clamp on the underside has four set-screws, an unpainted metal plate for protection, and that’s directly against the painted underside of the lip. What I need to do is take my roll of steel grounding strap and run that under the lip clamp, over to a bolt hole under the trunk decking, down to the trunk mount, and then underneath to the frame with some sort of lock washers and bolts to dig into the paint a little. Electrical conductivity is not the same as RF conductivity, and it’s for that reason that the ground strap is necessary.

If I still don’t get any better results, I’ll have to get an ATU (Automatic Tuner Unit) and put it electrically close to the antenna mount and run a line from that to the radio. Maybe even rewire the mount with a thicker cable. As long as the ATU can get a good tune, the radio won’t care and I might be able to run full power.

All antennas are compromise antennas. Too bad I can’t run a dipole on my car, eh? More news to follow.