AmateurRadio.com

Working new stations on 630m at this time of the solar cycle can be a rare occasion but two 'new ones' recently found their way into my logbook!

The first was Frank, K6FOD, in South Pasadena, to the north-east of Los Angeles. Now if Frank can have success on 630m in this densely populated location, then most amateurs should be able to have fun on the 630m band!

Frank is running about 200W output into a short inverted-L. Up until recently, his antenna was a large wire loop pointing east-west with which he had a lot of success working stations towards the east. He and I had several skeds while he was using the loop but since I was directly in the null of the loop, I was never able to detect a trace of his signal, nor was he able to hear me! The break through came when the vertical was erected ... but I'll let Frank tell more of the story ...

As a long-time shortwave listener I had always been very curious about the realm below the AM broadcast band, so not too long after I got my ham license in 2018 I started working on a 630m rig.

Most ops on that band use inverted-L antennas, but they are highly dependent on a robust system of ground radials. At my location, there just isn’t enough open ground to lay out an extensive radial network. This seemed like a show-stopper.

However, John Langridge KB5NJD, who was writing the MF/LF column for CQ magazine, suggested that I try a vertical loop tuned by a vacuum variable capacitor, which does not use a ground connection at the feed point. He mentioned that this was being used at the time by Ben Gelb N1VF. Between Ben and John, they helped out greatly on getting it going. Mine ended up with a circumference of about 100 feet.

By adding a 630m class D amp to my K3S, which has an internal 630m transverter, I was able to get on the air with digital modes, which at the time were JT9 for two-way QSOs and WSPR for beacon modes. The winter of 2019-2020, I worked a dozen ops in six states, the most distant being South Dakota. My WSPR signal was heard from Hawaii to the Cayman Islands.

Due to their size compared with the wavelength of the 630m band, loop antennas like the one I built are notoriously inefficient. Based on measuring RF amperage to the antenna, I calculated that it was sending only 47 milliwatts into the atmosphere. On the other hand, the winter of 2019-2020 was near a solar minimum, the point in the 11-year solar cycle when conditions are best for the low bands. And there was also a lot of activity on 630m that year because it was a fairly newly approved band and was attracting a lot of experimenters.

One downside of the vertical loops is that they are fairly directional, with a deep null off their sides. Because mine pointed east-west, it was exceptionally difficult to hear or be heard by stations due north.

After that experience, other parts of life got in the way, and I didn’t get back onto the 630m band until the winter of 2024-25. That winter, I used the same rig and vertical loop antenna as before, and worked eight ops in six states and Mexico.

But due north was still unreachable. Steve VE7SL and I gave it a good try, but neither of us could hear the other. So in the fall of 2025, despite my limited ability to lay out ground radials, I thought I’d give an inverted-L antenna a try. John KB5NJD again provided great guidance, and Steve VE7SL also lent very useful ideas.

At my location, going super tall wasn’t going to be feasible, so I ended up with a lightweight aluminum mast of 36 feet height. Because of my lot’s dimensions, instead of having one top wire to form the inverted L, I used two top wires in opposite directions, each 50 feet long — making what some call a “Tee Antenna.” 

Like inverted-L’s, its small size compared to the 630m wavelength meant it would require a substantial loading coil. I made this using a popular approach of a large coil wrapped around a 5-gallon plastic bucket, with a small coil inside it on a turnable rod, which allowed the total inductance to be adjusted. The big coil also had tap points. An impedance matching transformer was wrapped on a stack of four FT240-77 toroids. For a rig I decided to try an SDR transceiver which opened up possibilities of CW and SSB voice in addition to digital modes.

For the ground system, I tried laying out a set of 18 radial wires ranging in length from about 10 to 80 feet due to the site’s available space. My antenna analyzer indicated that R_feed was around 62 ohms. Measurement with an RF ammeter showed that about 1.25 watt was now getting into the atmosphere (this being the effective isotropic radiated power, or EIRP). The FCC limits 630m ham transmission to 5 watts EIRP, which means I have ample room for improvement, hopefully by adding however many more ground radial wires I can squeeze into my limited space.

After six weeks of operating in January-February 2026, this season I’ve worked six ops so far in three states and British Columbia. Hoping to add more if I can improve the antenna’s ground network.

When not in use for 630m, I’ve also attached the Tee Antenna to a multicoupler serving a small “skimmer farm” of SDRs that monitor FT8, CW and WSPR signals on ham bands from 630 to 10 meters. In addition, I’ve used it with an SDR for receive-only DX listening for non-directional beacons (NDBs), airport beacons that transmit below the AM broadcast band in North America. So far the Tee Antenna seems more sensitive than a number of other antenna designs I’ve tried for NDB listening. I also plan to use a remote tuner placed at the antenna to allow it to be used for CW, FT8 and voice QSOs on the HF bands.

Loading coil / variometer

Antenna impedance matching transformer

The other new contact was with fellow-Canadian, Karl, VE6KDX, in eastern central Alberta.