Category Archives: Amateur Radio

Things related to Amateur Radio, ham radio, the civil service, and similar hobbies and activities.

Year and a Day

Personally, I subscribe to the “one year and one day” concept in matters of learning a vocation, skill, belief, or hobby. During that period, a person is considered an initiate, a neophyte, a newbie. They may know a few things, but they’re only learning. They can’t be promoted to higher levels of trust during this lockout period; they have to pay with time and dedication. By no means are they to be considered a journeyman or a master of their class.

So January 20 came and went, and I forgot to write up a thing. January 20 is the one year anniversary of my first amateur radio grant, a Technician Class license (General Class upgrade came in April). I’ve been a ham for over a year and a day. I’ve gone through a heavy bit of learning by the books to shore up my knowledge and comprehension of radio communications, but the true learning comes by experience. I have to actually do the thing to know the thing, and this past year has been a lot of that.

I wish I knew more, did more, understood more, talked more, made more contacts. Even at my age, I feel like I still need to earn my stripes to gain some levels of respect in myself and from others. If I’m going to be talking the talk, I better be walking the walk. People ask me for advice, but more than half of it isn’t backed by any personal experience. Without experience, I’m just a blustery blunderbuss spouting off what I believe to be true. In the back of my mind, I can feel the real pros rolling their eyes when they listen in.

On my anniversary evening, I was asked to host the AARC ElmerNet because the usual host, Jeff N5MNW, was down with illness. I was glad for the privilege to do so, and thankful that he thought well enough of me to ask for a fill-in. I think it’s apropos that this happened on my year-and-a-day.

I’m no longer an initiate. I’m set loose from the nest to fly on my own. Learning is life-long.

So, from my QTH, to the F2 layer, and down to you all. 73.

Red Hot Radio

As it turns out, just like in audio engineering, in 2-way radio you can’t just look at the power meter and assume your signal is great. It might actually be unintelligible.

Back in my early days (6 months ago), I noticed that my RF power meter seldom hit 100W on voice. I know that the duty cycle of voice on sideband is significantly less than 100%, but even the peaks weren’t hitting it. Frustrated with apparently not getting my signal out of the region, I turned on the built-in audio compressor, tweaked the compression amount, and got that average power a bit higher to somewhere that looked right.

As I learned recently on the regional AARC 10-Meter Net (Sundays 3pm CT on 28.410MHz USB), my fellow net participants complained that there must be some RF feedback into my mic or something because my vocal peaks were seriously hot and distorted. They had been complaining for a few weeks, and I assumed it was some insufficient grounding in my car. While discussing it during a net, I mentioned that I had compression turned on; they asked me to turn it off, and the distortion went away.

Huh!

So, uh, remember that owner’s manual thing, and the part in it that tells the owner how to configure mic gain and compression? Yeah, so if I follow that, and look at the ALC (audio level control) meter instead of the RF power meter, and if I adjust things so the average and peaks stay within a specified range, then my signal should sound better.

I hooked up my dummy load, went to 10m sideband, spoke gibberish into the mic and tweaked the mic gain and compression amount to a range that makes sense (at least visually). I’ll try an A/B test on the next 10m net to see if it worked.

It’s not the output power that wins friends and gains contacts; it’s the signal quality. You can reach across the country on 10W if your antenna is good, the sky is right, and your signal is clean. Otherwise, you’re splattering your distorted RF energy across the band, you’re burning battery power, and you’re wasting someone else’s time.

Moving Ground

I did some rethinking on the power circuit for my two-way radio in the car. I had read multiple sources that connecting the 12V and Ground wires directly to the battery was the best way to minimize engine noise in the radio, so I went with that guidance and wired things directly to the battery terminals.

As it turns out, my assumption was half correct. The incorrect half could have set me up for disaster. According to an article written by W8JI, a situation could happen where — as a worst-case scenario — my radio is destroyed.

In the case that the radio is grounded directly to the battery, there are two connections coming from the negative post. One is a copper strap that goes from the battery post to somewhere nearby on the chassis body. The other connection is the ground lead to the radio.

So, if the chassis ground strap becomes loose, corroded, or disconnected, then everything in the car that’s powered will try to ground through the only battery connection left: the radio. This will result in instant destruction of its circuit traces and will damage the cable assembly until something either opens, melts, or catches fire.

The correct method for grounding the radio is to bolt the ground lead to a convenient place on the car body as close to the battery ground strap as possible. That way, if the strap breaks, the entire car loses its grounding.

I also learned that modern cars have sensors in the battery cable assemblies that measure how much current is being drawn from the battery. This signal goes to the ECU so it can command the alternator to produce more current. If the radio ground is connected directly to the post, it is upstream from this sensor and the ECU gets an incorrect measurement of current draw from the battery. Putting the radio downstream from this fixes that problem.

Foreground: battery ground post with current sensor. Background: new position of radio ground lead (blue) next to engine ground strap.

With these facts in mind, I made an adjustment to the circuit. I pulled the radio ground connector from the battery post and moved it down to a bolt that holds the ECU bracket. This bolt is mere inches away from the ground lead that goes to the engine block, so I know the connection is solid.

As an aside, I also see some guidance that I should take the fuse out of the ground lead circuit, but I’m not so sure about that. I’ll have to think more on it to figure out what will happen if the ground fuse blows. Will the radio have a floating ground? Will it continue to ground through the ground strap I’ve lashed to the radio body? Will I blow a circuit trace between the radio ground lead and the board’s internal connection to the radio body? I’m not sure.

More improvements to follow.

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.