HF Radio Aerial Experts Question

The rest of the aerial "Wire" length is wound inside the Auto tune, in your example for 8 MHz and your optimal length of 29 feet he has a 5 ft S/S whip then the Auto tune will adjust the aerial length internally for the other 24 odd feet.

If you cut the whip down you may not have enough length within the Auto tune to adjust to the optimal length.
I hope that makes sense??

Me I would leave the aerial lengths as supplied by the manufacturer or you could find that it won't tune to some frequencies.

Making the aerial resonant using the loading coil still won't make it as effective as a straight 29 foot whip.

The auto tune antennas don't have 24 feet of antenna inside, an auto tune antenna works like any standards antenna tuner.

The function of an antenna tuner is to effect a match between the output of a transceiver and the input of an antenna system. Modern transceivers can only deliver full power into a 50 O load. Antenna tuners are variable-impedance
transformers that allow you to transform the antenna system impedance (which can be almost anything) to 50 O for the transceiver. Some antenna tuners exhibit a wide impedance- matching range.

So in other words you are making the transceiver think it is perfectly matched to the antenna artificially.

As with most antenna tuners they can only tune so much and if the antenna is short for the tuner they will not tune.

An antenna tuner will not make a badly matched antenna work as well as a matched antenna.

A 5 foot whip on a auto tune base will be no match for a full length antenna .....if it was the case why would we still need big antennas when a short one would do just as well.

The difference between an auto tune antenna and a correct length antenna (1/4 wave length and up) could be anything up to 3 to 4 "S" points, to do this with just power alone you may need to increase the transmit power 2 to 3 times.

OK good info, Thanks I stand corrected on my understanding of the operation of the Auto tune, I have seen the long coil of copper wire inside them and thought by an explanation from someone else a long time ago (obviously incorrect) that they in effect shorted out this coiled wire to set the required aerial length.

I concede my understanding of the "S" points etc is zip :-)

Cheers

S = Signal strength from a scale of 0 to 30+, most signals are with in the 2 to 7 on average.

A station with a reading of S6 will be stronger then a radio with a S3 reading if using the same modulation level.

This is only a rough scale as it depends on Radios and S meter calibrations.

Much the same as a fuel gauge, it only gives you an idea and can vary from vehicle to vehicle.

John have a look on Wiki for a better understanding
http://en.wikipedia.org/wiki/Loading_coil

er..... should have added....I'm no HF expert.... just a seasoned user of such travel 'toys' :-o).