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2021 New England QSO Party

Call: N1TA
Operator(s): N1TA
Station: N1TA

Class: Single Op LP
QTH: FN32
Operating Time (hrs): 
Radios: SO2R

Summary:
 Band  CW-Dig Qs  Ph Qs
------------------------
   80:    281        
   40:    362        
   20:    276        
   15:     34        
   10:      3        
------------------------
Total:    956       0  Mults = 67  Total Score = 127,970

This was an interesting one. The day before the contest, my father (K1FWM) came over to test a new case of 806’s. While he was here, a microburst brought down the high catenary supporting both the doublet/T and the 20m delta loop. Thankfully, he hadn’t left yet and we were able to repair everything before dark.

The contest was uneventful. I decided to enter low power to compete for a plaque sponsored by the local club. Band conditions made for a struggle on the second day, and I never did feel like switching to phone; at half the point value for a phone QSO, there wasn’t any incentive!

Doublet with 160 meters

My new QTH (c. 2018) featured a long list of honey-do’s, pushing a real tower project back at least a few years. The good news was that it also featured very high pine trees; one particular specimen is at least 150′. I decided to take advantage of the high pine trees while daydreaming of aluminum.

The antenna is a typical doublet cut for 80 meters, about 130 feet long in total, and fed with open wire line directly to an MFJ-998rt autotuner at its base. The use of open wire line avoids the high loss characteristic of coaxial feedline at high SWR. The antenna supports are a 150′ pine at the south end and a 100′ pine at the north end, both placed by an arborist.

Although this antenna is higher than the average doublet, it still isn’t high enough to be competitive on 160 meters. For this, I knew that I needed a vertical. This can, of course, be done with some tricky switching: the open wire feedline is shorted together to form a Marconi-T against a radial field. It was a convenient surprise that the open wire feedline is about 120′ long, almost exactly 1/4-wave at 1.8 MHz!

Like most verticals, this antenna is only as good as the radial field beneath it, so I unrolled almost two acres of galvanized hardware screen during a yard remodel. I chose to use screen as opposed to radials due to the strange shape of the yard, although I have experimented with radials above the screen, both bonded and floating with little effect.

The antenna works well, probably because of its height. Band changes are a breeze, as a single dit on the paddle is often enough to trigger the autotuner memory. The relay box changing from doublet to Marconi-T at the base is operated by the radio band decoders, eliminating any manual switching by the operator.

After several months of using this setup and extensive testing with the Reverse Beacon Network, it looked like the antenna wasn’t great on 20 meters — and indeed I felt weak on 20 in contests. Instead of fiddling with the antenna any further, I hung a 20 meter delta loop near the top of the tall pine and it works significantly better for that band. It is positioned in such a way that there is no interaction with the doublet.

2020 WPX CW

Call: N1TA
Operator(s): N1TA
Station: N1TA

Class: SOAB LP
QTH: Massachusetts
Operating Time (hrs): 9:08

Summary:
 Band  QSOs
------------
  160:     
   80:     
   40:  171
   20:   64
   15:   65
   10:     
------------
Total:  300  Prefixes = 209  Total Score = 154,033

Club: 

Comments:

Just passing out QSOs. I'll get the station fully reassembled at some point.
Good to work everybody.

Proper feeding of non-resonant antennas

Coax becomes very lossy at high SWR. If you are feeding your non-resonant antenna (vertical, dipole, or any other design) with coax and utilizing a tuner at the shack end of the feedline, you’d be surprised by the amount of power you’re losing. Remember that your in-shack tuner does not tune the feedline to the antenna, and thus it remains at high SWR on most bands!

Balanced feedline, on the other hand, is very tolerant of high SWR and is practically lossless. It can be built inexpensively, and a variety of instructions exist online or in print. The cons of this cable type are well documented, but essentially boil down to users failing to maintain balance; if the feedline comes near conductive material, or is wildly blown about, it can become unbalanced and radiate. Despite the drawbacks, it is a demonstrably superior feedline for non-resonant antennas. Let’s compare common 600-Ohm balanced feedline against a few common types of coax:

600-Ohm Balanced Time Micro. LMR-400 Belden 8237 RG-8 Belden 8240 RG-58
Length (ft.)100100100100
Frequency (MHz)14141414
SWR3:13:13:13:1
Power In (W)100100100100
Total Loss (dB).12.721.031.95
Power Out (W)97.384.757963.8

The above chart assumes the SWR on your feedline is 3:1 — but it is likely to be significantly higher as with most non-resonant multiband antennas. Nonetheless, the 600-Ohm balanced feedline is clearly the winner. Let’s reexamine the results with a more realistic feedline SWR of 5:1:

600-Ohm BalancedTimes Micro. LMR-400Belden 8237 RG-8Belden 8240 RG-58
Length (ft.)100100100100
Frequency (MHz)14141414
SWR5:15:15:15:1
Power In (W)100100100100
Total Loss (dB).191.061.52.69
Power Out (W)95.8378.2770.9553.84

In this second example, the ham using RG-58 has lost almost half of his power in the feedline! With the high cost of radios and amplifiers, it seems silly to use lossy cable and sacrifice those expensive dB’s.

Differences in Balanced Feedline

Most amateurs opt to build their own 600-Ohm balanced feedline from wire and inexpensive spreader insulators. However, commercial 450-Ohm “window line” is available and very sturdy. Is it critical which one we select? Not particularly, as seen in the chart below:

600-Ohm Balanced450-Ohm Balanced
Length (ft.)100100
Frequency (MHz)2121
SWR5:15:1
Power In (W)100100
Total Loss (dB).19.27
Power Out (W)95.894

The 600-Ohm balanced feedline exhibits somewhat less loss, but the difference (even at 21 MHz) is negligible. If you must purchase a commercial 450-Ohm balanced feedline, you will be pleased with its performance.

Also see: W3LPL’s Coax loss charts

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