Tag Archives: antenna

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.

Backstop

I’ve heard of it being done, but I kinda secretly want to wire my radio and my antenna tuner to a softball backstop fence to see what kind of signal I can get out.

I have no idea if I can match the impedance of a backstop, or if I will be able to deal with the RF coming back down the feedline to my radio. I don’t even know if the fact that the backstop is anchored in the ground with concrete and touching the ground for its entire length will cause it to be its own ground plane. Does it act as a random wire antenna? Is it a longwire antenna? Is it good only for reception? What kind of harmful harmonics does it put out? How does the pair of 45º bends with the 90º straight legs affect the radiation pattern? What’s the optimum frequency band for it?

So what the hell…I gotta try it.

Hey, if someone can make long-distance contacts by wiring their radio, amplifier, and antenna tuner to a cast-iron skillet hanging from a swing set, I can make contacts with a backstop.

Stay tuned.

First QSO, First DX

So today was a crap day, but what happened when I left work and raised my antenna was a soothing balm that made everything alright. The good news is that today I made my very first HF contact (called a QSO) on the 20-meter band with my good radio. That’s a first. Also, on the very same contact, I made my first international contact (called a DX). On the same call!

Here’s a shout out to Gil VE2MAM from Quebec, Canada, who was calling CQ/DX to collect American counties. His signal was coming in strong and clear with a little bit of fading, so I decided to give it a try. I turned up my amp power, keyed up my mic, and responded with my callsign. He eventually heard me in the noise and we had an exchange of signal reports and a few other things like my location and county. I gave him a “59” signal report, meaning he was readable and had a strong signal. He gave me a “555”, meaning I was readable, my signal was fairly good, but there was some modulation on my signal (these can be dealt with).

I’m just happy that I’m finally learning how to make it happen. As it turns out, the modular vertical antenna I’ve been using (which is ultra-portable) isn’t so good for making anything other than regional contacts. It’s easy to set up and tune, but it’s just not that efficient at putting out a radio signal. What i did tonight was string my 20-meter dipole between two trees in Mueller park. It took me a little bit of trial and error to throw the ropes high enough and get enough distance between trees so the antenna wasn’t in the branches, but I figured it out.

Gil, I certainly hope your log of our QSO doesn’t need me to submit a log from my end for you to get credit, but it was nice talking with you. 73, good sir. Merci!

First QSO, 14.289MHz 20170609 0:00 UTC

20-meter dipole strung between two trees