[copied from my wsprnet.org blog]
Today, I think for the first time, I have unleashed one of my "old ladies" into WSPR action.
The "old lady" I am referring to is an FT-101ZD Mk3 which I brought back from the dead a few years ago. An EBay "tech special" in US terminology, or "spares or repair" in terms of UK terminology.
This features on my web site (www.g4fui.net) so I won't repeat too much I have already covered elsewhere, but I think I have proved to myself, at least that these old radios can, with care be used reasonably successfully on today's modern computer-generated modes.
I have been spotting stations with this radio for a couple of days, and today, I enabled transmission and others have spotted me.
The principal disadvantage with the older radios is that of frequency stability, or rather the lack of it.
On my "to do" list for this radio is to (hopefully) improve this facet, probably by replacing the zener diode based voltage stabiliser to the VFO with something of somewhat higher specification (eg low-dropout IC regulator, or similar) as this is where I think the thermal stability weakness lies with this particular radio.
However, having allowed the radio to warm up for some considerable time (four hours) the case temperature of the radio is still gradually increasing but at a very gentle rate. Yesterday the case temperature crept up ALL DAY, as did the VFO frequency error!
Nevertheless, I regard the performance as just about good enough for me to join in the WSPR fun. The results will be stashed away in a spreadsheet on my PC and used in a "before" and "after" type comparison once I decide to tackle the thermal stability issue.
In the meantime if any other WSPRers are wondering why their "drift" as received at G4FUI isn't quite as good as they think it ought to be, then the above hopefully provides some sort of explanation!
I don't think that cranking the power down to half a watt from a tube PA is necessarily all that "green", as the PA efficiency must be abysmal, however it probably is a good idea to run the tubes for a few hours to keep the vacuum in them nice and hard!
5 hours ago