On Sat, Sep 17, 2022 at 04:35 PM, Dr David Kirkby G8WRB wrote:
Its also corrugated, so I would expect the resistance of it to be higher than straight tube of the same diameter and thickness.?
Not by so much, perhaps 5%, from memory Owen Duffy has some calculations somewhere.
Inductance is slightly higher too.
Aluminium ducting tape is a definite NO from me.
Coper flashing is another option, if you can get hold of it, which doesn't seem to be that easy in the UK.
I tend to use LDF4-50, sometimes connected in parallel, but I think Simon's suggestion of Aircon tubing is a good one.
If your tuned loop transmit is working efficiently, it can be quite hazardous at close distances, fortunately from a compliance / H&S perspective most don't work that well, saving folks from serious harm to themselves and others.
I have a theory about transmit antennas, that folks don't notice how inefficient they are, unless they perform about 10dB worse than the user expected them to be. So losses of just a few dB tend to get ignored.? Most home built, and even a lot of the commercial tuned transmit loops are not that good (as it costs money to properly engineer one that works well), but if the performance is 'good enough', folks don't worry, or bother to try and measure their actual efficiency.
In many cases for amateur builds, 'screwdriver' type tuned whips are easer to construct and tend to be more efficient (especially on the LF bands), because they don't require such heavy engineering to minimise losses.
Just my 2p worth...
Regards,
Martin
