Thursday, 8 May 2008

Unreasonably good results...
The 160m transmitter had its first serious outing tonight. I called into the local net (qv my first post), and two local stations (one around three miles away) gave very positive signal reports. My thanks and 73's to G4FFE and G3NDJ for their reports. A third station, in Shoreham, couldn't hear me; but I'm not surprised. I was running just 100mW (I lost two thirds of my signal when I removed a badly-terminated inter-stage filter), and the results astounded me. I intend to call a CQ or two once darkness falls, when great things can happen on Topband.

I must find out why I lost so much signal when I removed the filter. It was installed in error; I fitted a 7MHz 3-pole pi-filter, designed for 500-ohm termination, between the second SA602 mixer and the pre-driver. This point is at 1500 ohms, and so the mixer and filter were both miss-terminated. I should have put it between the pre-driver and the BFY51 driver stage, where things are at 500 ohms. In theory (a naive theory, mind you!), this was potentially losing around 4dB of signal, and removing it should have given in increase in output. Ho-hum. Work needed here; I really could do with around 500mW or more coming out of that BFY51, ready for the FET PA to boost to the 5W I think is right and proper. If I can give a station three miles away a 59 signal with 100mW, I can cover most of Sussex with 5W. Well, that's what I intend to try to prove.

A dalliance with virtual radio
I tried to use an Internet radio system called Hamsphere. It works, and is an many ways realistic, and I made conversation with some people. One was a licensed UK amateur, another a US licensee, and the third a nice chap called Jacob from the Netherlands. G0THD sounded like a strong, local surface-wave contact, as expected since we are physically separated by only twenty miles. The Dutchman faded in the way that European stations do on 40m in the evening, but WA1JPG should not have been heard. I mean that in the nicest way! He was helpful and friendly, but I can't hear US stations on 40m, day or night. It's also a little weird hearing the old Woodpecker rattling away from time to time; this OTH radar system hasn't been heard in years.

All in all, Hamsphere is a great way of providing unlicensed enthusiasts with a way of trying out their operating skills, without resorting to piracy. It's also a pleasant way of allowing those hams who simply cannot (for whatever reason) operate 'real' radio equipment to contact others in an authentic-sounding way, with just an Internet-connected PC and a headset.

Noise noise noise noise
Noise is the enemy of efficient communication. My latest PC (a Dell L400 notebook with a bad flat-panel) is a quiet computer, but its attendant switching power supply is a screaming, roaring noise source. I can run the Dell on its internal battery while operating, but that only lasts an hour. Today, however, I found a possible solution in the scrap-metal skip at the saltmine. An old 24V soldering iron station, minus the iron, but capable of supplying enough current to run the laptop. I need up to 1500mA at 19V. The computer would normally use more, but the absent flat-panel display may account for a lot of the power used. When the batteries aren't charging, it only draws 500mA. This is a big improvement on my previous laptop, which drew 1400 to 1700 mA all the time. So, after finishing this here post, I'll see if the thing works, and then incorporate an LM317 on a big heatsink, set for 19V.

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