Many thanks to John (N3AAZ), who shares the following notes from a recent antenna project:
Hi Thomas
For what it’s worth, here’s an easy, cheap, very lightweight, multi-band, no counterpoise antenna for portable ops.
This build took place on a rainy day at a campground in an 18ft RV and was inspired by an article written by Craig (WB3GCK): No Counterpoise Speaker Wire Antenna.
This antenna can be set up as an inverted V or inverted L.
I cut a 30/20 ft version to hang on a 32ft Jackite telescoping fiberglass mast. I read that several ‘random’ lengths, the 50/25 and 25/17, have also been successful.
Cut a 30 ft length of speaker wire (do not peel or separate it yet), then measured back 10 ft and peel off then cut only one side of the speaker wire twin lead. This will effectively create a 30-foot antenna with a 20-foot “balanced” feed.
You will then need a “BALUN” with unbalanced input and balanced output.
My 1:4 and 1:9 did not work because both ports are single-end BCN connectors soldered on a PCB.
Luckily, I also pack an MFJ 9211 (1:4 QRPocket Current Balun).
Using a NanoVNA and MFJ-902.mod.aaz (mod to form an L-network–more info on my qrz.com page) I measured less than 2:1 SWR on 40, 30, 20, and 15 meters.
The N7DDC ATU-100 reports…
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- 1.18 :1 SWR on 15M
- 1.03 on 20M
- 1.16 on 30M
- 1.88 0n 40M
It loads well.
My first 20-meter contact was a POTA contact with W4TTU (approximately 700 miles away), who gave me a 559 at 5W–he was 579 and signed “72,” so I assumed running QRP as well.
Not too shabby for an impromptu rainy day project hi hi!
72
John
N3AAZ
Thanks for sharing these notes, John! This looks like a fun little antenna build.
How does one setup the nanovna to read the SWR across multiple bands?
The nanoVNA has multiple calibration slots that can be saved and retrieved. You can either use one slot and set the Start and Stop of the Stimulus to be a large range, e.g. 6-29 MHz, or use multiple narrower slots, e.g. 6-8 MHz, 9-11 MHz, etc. I prefer the second setup because you loose some resolution with a larger range and I have five different slots calibrated for each of the common bands I work with.
Would this work for SSB voice? Did John happen to test voice?
Great idea. I also built a speaker wire antenna. I marked of 28 feet and cut it from the spool. Split and separated the wires into 2. Used the same antenna connectors you showed.
From the Outer Banks, NC, I made a QRP contact, on 20 meters with a PA station, on 5 watts.
They are great projects and I have enjoyed mine. 73s and have a great day de KD8VSP.
Great write-up. Going to have to give that antenna a try. I do 35ft but lay the counterpoise on the ground.
Dennis
W0HL
Hi John, your antenna reminds me the HB9XBG
https://en.wikipedia.org/wiki/HB9XBG_Antenna
that one is an half wave vertical, using one of the two wires as the counterpoise, in your case you applied the idea to a “random” wire, nice idea; it would be interesting to play with the “counterpoise” (shorter wire) length to see if it’s possible to obtain a better impedance match
Success loves company! While I have a commercially built version of this antenna for 80-10m and 40-10m and 20-10m I built my version on this 30/20 ft antenna thus rainy Thanksgiving. I built mine with a home brew 4:1 Balun.
This antenna will be used for FT8 sorties as supported by my 20-10m QDX transceiver and ny recently built DX-FT8 QRPp trans-tablet rig for 20-10m . SWR measurement must wait for a drier day. But I am confident it will test well based on using the commercial versions.
Since I had everything in inventory in the shop, there were no immediate out of pocket expenses; just “sunk costs”. Building a sundry of QRP antennas brings joy to me every time.
72
Paul -W2PB
oh and a note, a vertical longer than abt 6m will have a high takeoff angle on 10 to 12 m bands, while it will have (if longer) more efficiency on lower frequencies (no surprise), so…. if someone is considering a vertical “all bands”, for exsmple a “random”, go for an inverted L setup, with the vertical portion 6m or less
Thanks for the info! I have a POTA33 mast on the way and I have speaker wire and a 4:1 BALUN. I will probably give this a shot next week!
N7BBQ
I love simple. This is simple. I usually make a doublet of speaker wire. But I’ll give it a try. TU 72 de W7UDT ID sk ee
My follow up on this project
The CURRENT (not Voltage) BALUN is required
This 1:1 CURRENT BALUN works best for me
https://vk6ysf.com/balun_guanella_current_1-1.htm
Also note a tuner is required
My tuner is in the shack and a simple common mode choke (clamp on ferrite) between the BALUN and coax feed makes for outstanding repeatable results from one site to another
Also note this type BALUN can be d.c. coupled to Earth (no bleed resistor required) to prevent high Voltage static dishcharge through receiver front end
Just connect coax shield to station ground
72
John
N3AAZ