Hearing through the noise on the low bands

Be sure to read the companion post: Matching transformers for “loop on ground” and Beverage receive antennas

In my opinion, it is easier to get a signal out on 160M than to hear weak stations.

Prolific atmospheric noise and the inefficiency of small antennas on a band that really needs a lot of wire in the air mean many of the stations you may want to work are little pistols in the grand scheme of things.

You’ll hear high-power stations as their brute force will push through the noise, but those pip-squeak stations will be buried under the hiss and hash of band noise unless you can significantly improve the signal-to-noise ratio in your receiver.

Signal-to-noise improvements

To improve the signal-to-noise ratio on 160M and 80M, many of us use a separate low-noise receive antenna. The classic Beverage – a wire many hundreds of feet long, either a few feet off the ground or even right on the ground – is popular, as are active and passive loops of various kinds. The K9AY loop, flag/pennant or EWE antennas are also commonly employed to hear weak signals by dropping the noise floor so stations pop up out of the noise.

Again, a really great roundup for information about low-band receive antennas has been published by TopBandHams.com.

At this QTH

What do I use? Well, I have a short Beverage antenna that runs about 270 feet from west to east along my property line. It is about five feet off the ground, and its 450-ohm impedance (measured between the wire and ground) is matched to 75-ohm RG6 coax feedline using a 6:1 matching transformer.

Specifically, that transformer consists of a small BN-73-202 “binocular” ferrite corethey sell for $0.95 apiece on Amidon.com – with two turns of 24-ga. magnet wire for the coax side, and six turns for the antenna side. To repeat: that simple little transformer matches the antenna’s typical 450- to 550-ohms of impedance (on 160M) to the coax’s 75-ohm impedance.

Above: inside one of my latest builds — a very small matching transformer. This one uses a Fair-Rite BN-73-202 ferrite binocular core and 30-gauge enameled wire — two turns on the F-connector side (so I can attach 75-ohm RG6 coax) and six turns on the high-impedance side (the two ends of a loop on ground, for example).

The red dot marks the high-impedance end of the transformer, and indicates the core material “73” and the 2:6 turns ratio.

Below: a close-up of a couple of small matching transformers — the are both 2:6 turns on binocular cores.

Beverage feedpoint grounding matters!

When I first installed the Beverage in 2009, rather than putting in a ground rod I simply grounded the antenna to the chainlink fence as it was handy near the feedpoint. At that time, I was using a 2 turn/5 turn matching transformer. About a year later, I added a 4-foot copper ground rod, and the antenna impedance went from 210 ohms using a chainlink fence as a ground point to 410 ohms with the copper pipe.

I added a single extra turn on the transformer’s secondary winding and — measuring resistance through the matching transformer — had 49 ohms for the coax on 160M and 53 ohms on 80M.

The change in noise reduction wasn’t super dramatic on 160M — noise was still S3 or so (S7 or more on the transmit antenna) — but I was startled to hear the difference on 80M, where noise was virtually undetectable and signals were strong and seemed to almost float in the silence.

Audio from the Beverage

Listen to KH6LC on 80M (.mp3 – 264kb) at 0500Z

The audio opens with KH6LC on the Beverage antenna. You’ll hear when I switch to my 2-element vertical array pointed due West (almost exactly at KH6 from VE7). The difference in noise is dramatic — and it disappears again when switching back to the Beverage antenna.

No room for a Beverage?

The loop-on-ground (or LoG) antenna is an old-time idea reinvigorated and enhanced in recent years by KK5JY’s article in 2016. Matt has sparked a whole new era of interest in this remarkably simple, cheap yet effective receive-only antenna for the lower bands.

Lay a wire on the lawn in a square shape with 15-foot sides, hook it up to some 75- or 50-ohm coax through a 4:1 or 9:1 (respectively) matching transformer then as fast as you can run inside and see how much improved signal-to-noise is on 160M or 80M.

I built one, and once I got it working (it required multiple 6-inch loops of coax bunch-wound as common mode chokes at the feedpoint and at the shack-end of the coax feedline) I couldn’t believe how effective it was at reducing noise and allowing weaker signals to pop up out of the background.

Read the original Loop-on-Ground article by Matt KK5JY

More great resources

Watch for more detailed posts about my receive antenna experiences. Here’s one about building matching transformers for my Beverage and loop on ground antennas (note: that post includes audio recordings of the loop on ground on 80M compared with a full-sized vertical, and on 160M compared with an inverted-L).

Also, be sure to read VE3VN’s Pattern and Match post on Beverage matching transformers – it’s a great tutorial as Ron walks through building a transformer using the BN-73-202 binocular core.

I feed both the Beverage and the loop on ground using 75-ohm RG6 coax, which is both cheap and available at any big box store or your local surplus shop.

Neither antenna at my QTH is perfect – sometimes they don’t seem to help at all, but at other times they’re the difference between copying a caller and not hearing them at all.

The short Beverage works but you really have to experiment with the matching transformer values. Same thing with the Loop on Ground. If you have an antenna analyzer – or a nanoVNA, which is what I use these days – use it to determine the antenna’s impedance.

  • For the Beverage, you can measure the impedance between the Beverage wire and your grounding rod/ground point.
  • For the Loop on Ground, just attach the analyzer or VNA to the loop’s  two feedpoints.

Knowing what that impedance figure is, you can determine how many turns to wind on your matching transformer.

Check Steve VE6WZ’s excellent – and very helpful – video tutorial on using an analyzer to sweep your Beverage wire.

Summing up

Experienced Top Banders and contest operators use separate transmit and receive antennas. A good low-noise receiving antenna will do more for your score than using a high-powered amplifier without tackling band noise and local noise sources in your receiver.

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