W6IWI

The call letters W6IWI were first used by Kauko Hallikainen in the 1930s. See the 1938 Amateur Radio Callbook. The 1930s QSL card was similar to that shown above (I may still have one of the originals somewhere). 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 Noise

Notes on resolving power line noise have been moved here.

Receiver AGC vs Input

To get an idea of signal strength, data was gathered on AGC voltage (actually AGC count captured from the EIA 485 bus between the radio and the control head) versus receiver input level at the center of each band. A SARK-110 (thanks to Jack, KE0VH for the loan of this excellent instrument) antenna analyzer was used as a signal generator to drive the SEA 245. The raw data is shown here. A plot of the data for 40 meters, as generated by https://mycurvefit.com/ is shown below. This was generated with an auto-smoothed spline fit. It is extended down to the measured noise level on the receiver (AGC count of 10 corresponding to an input level of -118 dBm. From this curve, the 40 meter noise level measured above (AGC = 118.2) corresponds to a receiver input level of about -92 dBm which is 26 dB above the receiver internal noise. S9 is defined as -73 dBm with each S unit being a change of 6 dB. On 40 meters, an input level of -73 dBm gave an AGC count of 184. The power line noise of -92 dBm is 19 dB below -73 dBm or 3 S units below S9. The power line noise is, therefore, about S6.


Based on the data above, a 30 dB increase in the linear region results in an AGC count increase of 98. This indicates we have 0.306 dB/count.

Antenna Analysis

Since I borrowed the SARK-110, I may as well look at how my antenna and tuner work. The antenna is a multi-band inverted V with the center up about 25 feet. It has wires cut for 40m, 20m, and 10m. The 40m is oriented east-west. The others are pretty much north-south. They are all fed with a single 50 ohm coaxial cable with no balun. The coax is about 30 feet long with a lightning arrestor about 5 feet from the antenna tuner at the base of the mast. The lighning arrestor is at the top of a ground rod that goes down 8 feet. A wide braid connects the ground rod to the antenna tuner.

Below is a Smith chart plot of the antenna (at the bottom end of the transmission line, where it connects to the tuner output) from 1 MHz to 29 MHz. The minimum VSWR is at about 13.97 MHz where the impedance is 50.6-j .09 ohms. The green portion of the plot is for frequencies below the mid-frequency of the scan (15 MHz), and red is for frequencies above. The red circle in the middle corresponds to a VSWR of 2.0.

The table below shows an R+jX and VSWR sweep of each band from 160m to 10m. The left columns show the impedance and VSWR at the radio (before the tuner) after the tuner autotuned to the center of the band. The right columns show the antenna impedance as measured at the output of the tuner (before the transmission line going up the mast about 25 feet).
BandImpedance at RadioAntenna Impedance at Tuner Output
R+jXVSWRVSWRR+jXVSWR
160m
80m
60m
40m
30m
20m
17m
15m
12m
10m

.

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!

Fun Stuff

Contact

Contact me with any comments at harold@w6iwi.org.