In a recent blog post I discussed tuning my short 75 foot (15 ft vertical and 60 ft horizontal) Inverted L with my BC306-A variometer. So yesterday I set up a sked and worked K3MF on 473.6 kHz, using CW. Wayde was 599 at my location, and I was 449 at his. I was running somewhere between 25 and 50 watts to the inverted L. I am not sure which, because the ENI 1040L amplifier said I was putting out 25 watts, and my Nye Viking MB-V-A Antenna Tuner said that I was putting out 50 watts. So we don’t know if my EIRP was 72 milliwatts or 145 milliwatts (calculation done using http://www.472khz.org/pages/tools/antenna-simulator.php):
The ENI 1040L amplifier has 55 dB gain, so 1 mw in gives 500 watts out. I am not yet ready to run 500W, because I don’t think that the BC306A variometer would handle that. John, W3HMS and I both guessed that it would handle about 150 watts, but I want to play it safe and so I have not run more than 100 watts transmitter output at this point, which would give me an EIRP of about 291 mw. That “100 watts” is however the Nye Antenna tuner reading, because I want to be conservative, so it might be that my maximum power out has been 50 watts, giving an EIRP of 146 mw or so. The ENI 1040L amplifier is rated for 500 watts out at any SWR with any phase angle. It has a very simple front panel: AC On/Off switch, Power and Overload lamps, BNC RF input and output, a power meter, and a meter switch for either forward power or power delivered to load:
I started off using CW because the first test of digital modes showed that with this high-gain amplifier even when running just 50 watts TPO (transmitter power output) there was enough RF getting into the USB cable running between the computer and the radio so that the TPO jumped up to 200 watts when my Elecraft K3 was put into transmit without any audio input. This had never happened with any of my VHF/UHF/microwave work, even when running 1500 watts JT65 on 144 MHz. This occurred even though I had fed the USB cable through some cylindrical toroids.
I got a good recommendation on a particular shielded USB Cable with built-in ferrite chokes at each end Tripp Lite USB 2.0 Hi-Speed A/B Cable with Ferrite Chokes, so I ordered some of those from Amazon and they arrived today. I installed one of them between the computer and the Elecraft K3, and I also improved my station grounding by running thick braid between the radio and the computer, the radio and its power supply, the radio and the amplifier, the amplifier and the Nye Antenna tuner, and the Nye Antenna Tuner and the copper bus bar that is connected to the building safety ground and to the extensive ground rod system that surrounds my building. Slide # 103 of this presentation shows you what you need to do. A fairly common practice of running each piece of gear individually to a common point is NOT the proper way to do this. See this pdf file by Jim, K9YC: http://k9yc.com/GroundingAndAudio.pdf
After installing the new USB cable and improving my station grounding, I have no problems with RF getting into things, at least up to 100 watts TPO or so.
I only had time to run 4 transmit WSPR cycles today before needing to return home for dinner, but I was able to get decodes on each of the 4 periods from W4KZK who is in EM97 at a distance of 538 km, 4 decodes from W3LPL in FM19lg at 145 km, 3 decodes from N3FL in FM19ua at 142 kM, and 1 decode from KJ4BYS in FM28bh at 218 km:
Next steps will be to improve transmit antenna and build a higher power variometer so that I can run more power.
73,
Roger Rehr
W3SZ