In article , Frank writes:
If your fabrication skills are good, you could construct a tuned loop for SW. There's plans on the web and youtube videos. I think you'd be able to get by without the coupling loop, just put the radio close to the antenna, in the right direction, and

The problem without having an antenna input is that you do not have
any specs for input impedance, All you know is it is almost certainly
_not_ 75 ohms.

If you think about it, a quarter wave antenna for 30 Mhz, by the hams'
rule of thumb L = 234/f, is 7.8' . It gets longer for everything else,
up to 250' or so for the broadcast band. This means a high negative
(capacitive) reactance, typically, is expected at the input circuit,
and if they were to tune some of that out with an inductor they would
see a low, resistive, source impedance feeding the RF amp stage.

That's about as far as I am able to analyze this, but I would
recommend an SWL antenna tuner, which is likely capable of adjusting
to anything from a random wire to a multielement beam. The manual
may just tell you what you need to know about feeding the receiver at
the whip antenna input point.

I'm out of touch, but I think MFJ, and maybe Ten-Tec, might have
had such tuners in the past. There may also be preselectors -
basically RF preamps - in case your receiver does not have
a high performance RF input stage.

The ARRL Handbook, and the Antenna Handbook, will both have
sections on antenna couplers. A simple L network is basically
only two components, with at least one of them being tunable.
The trick is choosing the components and their configuration,
and that's where the commercial product comes in: they've already
worked out compromise values.

After that, the actual antenna you decide on is not so important.
You can start with a random wire and move up to something more
sophisticated.

George