W6IWI

The call letters W6IWI were first used by Kauko Hallikainen in the 1930s. See the 1938 Amateur Radio Callbook. I acquired the call in 2016. Prior to that, I held the call WA6FDN, and prior to that, WN6FDN. The WA6FDN license was probably first granted in 1967 or thereabouts, with WN6FDN a year earlier.

WN6FDN started with a Heathkit DX-60 transmitter and a National NC-300 receiver running CW on HF. WA6FDN used a Viking Ranger transmitter running AM, CW, and RTTY on HF. RTTY used a Teletype model 15 printer, and a model 14 typing reperf and transmitter distributor. W6IWI now uses an SEA 245 running CW and SSB into an inverted V antenna in Arvada CO. VHF and UHF FM are covered with a Baofeng UV-5R and a Wouxun KG-UV-6X

W6IWI HF Activity

The plot below shows a historic plot of W6IWI HF CW activity.

Recent activity (in the past day or so) can be viewed here. These are both generated by the Reverse Beacon Network.

Power Line Interference


The image above shows the output of my SSB receiver tuned to 7.000 MHz LSB. The trigger is the AC line. The image is stable with this trigger indicating that the noise is synchronized with the AC line. Further, the noise peaks are about 8 ms apart, in sync with the half period of the AC line (8.333 ms).


The plot above shows the receiver (tuned to 7 MHz LSB) AGC voltage over a 24 hour period (Sun Feb 04 16:06:43.103 2018 through Mon Feb 05 18:25:37.946 2018). At Mon Feb 05 15:43:41.673 2018, the antenna was disconnected to see what the reading was due to receiver noise. With the antenna connected, the average value was 118.2. With the antenna disconnected, the average was 10.2. So far, I do not have the relationship between receiver input voltage and the AGC value. Looking at the scope photo, it appears the power line noise is 6 to 12 dB above the other noise (voltage at power line spikes versus noise between spikes).

An ARRL power line noise mitigtation form is available here. A report of the noise was submitted on 2/10/18.

Web SDR

Until the power line interference issue is resolved, most HF receiving is done using Web SDR. A truly amazing project that lets you listen to receivers around the world. See here for a history of early web SDR hardware. In its basic form, a web SDR is a high speed ADC (for example, the LTC2216 16 bit ADC running at 77.76 MHz) driving an Ethernet interface to a server computer. The server provides a user interface to multiple users, demodulates the user chosen frequency, streams the resulting audio, shows a waterfall plot of the surrounding spectrum, and many other features. To me, this is truly amazing! The web SDR may also decrease the Ethernet bandwidth requirements between the ADC and the server by only sending selected frequency ranges (bands). In this case, digital down converters are included in the FPGA between the ADC and the Ethernet PHY. Just as in analog, a digital down converter multiplies the incoming RF by a "local oscillator" and filters the output to the desired spectrum (and removing the image). The local oscillator is a direct digital synthesis sine wave generator (a phase accumulator determines the phase of the local oscillator at each clock edge. The phase is passed to a sine lookup table to generate the sine wave local oscillator signal). "Mixing" is just multiplication of the sine wave local oscillator with the incoming RF. The resulting product is filtered (often just a low pass filter) to remove the image and define the received band. Resulting samples can now be down-sampled since the highest sampled frequency is lower than with the incoming RF. This reduced bitrate signal is sent over Ethernet to the server for further processing. Again, truly amazing!