130 ft Doublet Antenna, covers all nine HF bands 80m - 10m, and optionally 160m with reasonable patterns.
600 ohm feeder > 1:1 ATU balun > switching network > Remote antenna coupler / tuner.
The conundrum I had was how to get all nine HF bands 80m - 10m, and 160m from one antenna, with reasonable patterns, performance, and rated for high power. My limitation is having 1/4 acre where I can fit at most 130 ft of wire in a straight line horizontally.
Decided a doublet fed with 600 ohm open line into a remote ATU was the best option. Also, linking the feeders together and driving it against ground as a T antenna enables use on 160m, and a useful set of alternate patterns on 80 through 40m.
The matching network we bring into the 21st century, high quality remote ATU and high quality 1:1 ATU current balun. Remember, any system is only as strong as the weakest link..
- Balun Designs model 1171 5 kW 1:1 ATU current balun (studs in, studs out).
- Remote ATU Stockcorner JC-4s 1 kW automatic antenna tuner (5 stars on eHam).
- Doublet and feeder from TrueLadderLine. Could built it, cheaper to buy it vs time.
The JC-4s ATU can be interfaced to Kenwood and Icom rigs to operate via the Tuner button, and setup to bypass keying an amplifier during tuning. See JC-4s Automatic ATU and Icom IC-7300 Hints on PA0FRI's site.
Initially tuner was very slow to find matches on the upper HF bands when interfaced to the Icom ATU port, but was very quick using the supplied manual tuner interface and 15W carrier to tune. The TUNE carrier power in my Icom 7300 was under 10W, raised it to around 15W the per the service manual which solved the problem.
T Antenna mode, this turns it into a vertical with top loading by feeding the two legs of the feeder together against ground:
- 160m - 1/8th wave vertical, top loading results in uniform current along the vertical.
- 80m - 1/4 wave vertical, top loading moves current max to top away from ground noise.
- 60 to 40m - not sure how you would describe it.
So, how does it work? I had it up on Oct 21 but connected to my Icom AH-4 tuner which limited me to 100W while I waited for the JC-4s. With the 100 ft feeder strung up to the AH-4 in a temporary location it tuned all bands except 160m.
The first thing I noticed was how much quieter it is on receive compared to my OCFD which had a Balun Designs OCF balun optimized for the job with a good amount of current choking. Now I wonder how much noise is picked up by the coax shield and leaks or couples past the balun to the antenna, then back into the receiver? Noise dropped two to three S units between 80 and 20m.
So far the results on 12, 15, 17, 20, 30m have been good on FT8. SNR each way mostly equal, and looking the TX/RX performance with other stations in my grid on pskreporter things are fairly comparable.
Morning of 22 Oct 21 I worked 8J1RL Antartica on 40m FT8, about 1 hour after sunrise.
Confirmed in LoTW so not making this up :-)
That I managed to get those three rare ones with only 80W TX on my end was a nice surprise.
Weekend Oct 30 was CQ WW SSB contest, we had some good propagation on the upper bands. Saturday I worked a number of stations on 10m SSB with 100W in South America, Caribbean, and Japan late in the evening. KL7RA a well known contest station in Alaska commented I had the biggest signal on 15m they'd seen.. Probably something to do with one of those 9.8 dBi lobes that falls north west :-) also worked them on 20 and 40m. 9/10 times I'd get heard on the first or second call, following morning on 20m got OH8X (super station in Finland), and a couple others.
Also got excellent reports on 75m AM running "bare foot" 25W carrier power.
13 Nov 2021, I now have the JC-4s installed, and feeder length tuned for good matches on all bands, I used my RigExpert to do this so I can be sure that complex impedances the tuner sees are reasonable.
14 Nov 2021, I see Kuwait operating on 20m FT8, watched for a while no decodes. Checked again an hour or so later, decoding up to -6 dB, tried for 10 - 15 minutes with 80W, no luck. Hit it with 400W and completed the contact. I had to pick my self up off the floor when the RR73 appeared. From my location near Seattle, Kuwait is right over the north pole, middle of day here, night there. Unbelievable.
I'm suspiciously optimistic this antenna just seems to work better than all previous wire antennas I have used by a good margin (dipoles, trapped dipoles, OCFD), it keeps surprising me.
Actual readings taken with a RigExpert analyzer connected to the 1:1 ATU balun in doublet mode:
Band | R Ω | X Ω | SWR |
10m | 162.2 | -93.9 | 4.4 |
12m | 136.3 | -114.1 | 4.8 |
15m | 56.7 | -178.6 | 13 |
17m | 35.7 | -163.1 | 17 |
20m | 52.7 | -259.6 | 28 |
30m | 486.0 | 151.9 | 11 |
40m | 102.4 | -442.2 | 41 |
60m | 98.1 | 109.8 | 4.7 |
75m | 137.9 | -445.6 | 32 |
80m | 313.5 | -659.6 | 34 |
160m | 12.0 | -141.9 | 38 |
This is with the antenna at a height of about 55 ft or 17 m, and approx 70 ft or 21 m of 600 ohm open wire line.
This shows me that the ATU has quite reasonable complex impedances to match, or no wild extremes at least.
R is a little low on 160m but at 130 ft or 40 m long the doublet is well too short at 1/4 wave length, but it does work no doubt with reduced efficiency. In T mode on 160m it would work much better as a DX antenna on transmit at least..
This also highlights the trap of assuming a 4:1 balun should be used, in nearly all cases this would lower the impedance too much. See Tuner Balun 4:1 or 1:1 for more about that.
Introducing the "All Band" Doublet - Cebik.
10 Frequency Asked Questions about the All-Band Doublet - Cebik.
Tuner Balun: 4:1 or 1:1? - G3TXQ.
80-Meter Doublet - KV5R.