13-03-2013, 01:48 PM
Thanks Joe - that's what I suspected - but I thought I'd just check first. 
I can understand your thinking: the ferrite rod isn't fully effective on account of the break in it, so use the external loop to get a bit more signal from distant transmitters into the radio. But depending on how you couple that loop to the radio, doing that is likely to mess up the alignment of the 'front-end' R.F. tuned circuits - and that may well explain some of the results you have obtained. The first R.F tuned cct. is expecting to 'see' just the right amount of inductance and capacitance as the set is tuned over its frequency range. By introducing the loop, that inductance has now changed (the amount of change largely dependent on the degree of coupling from the loop to the set), so consequently, the 'front-end' tracking will be thrown out of alignment, and that mis-alignment will be frequency-sensitive, of course.
The most effective remedy, of course, is simply to replace the broken ferrite rod.
As for sets that do not use a ferrite rod, but with an 'internal aerial', that aerial will still comprise a critical-value inductance for the first tuned cct. in the set, so the above comment is still applicable.
For valve sets that are designed for the traditional 'longwire' running down the garden, then yes, I can see that a loop (of almost any dimensions) will be beneficial to some degree, if the traditional '100-foot longwire' is not available.
HTH,
Al. / March 13, 2013 //
I can understand your thinking: the ferrite rod isn't fully effective on account of the break in it, so use the external loop to get a bit more signal from distant transmitters into the radio. But depending on how you couple that loop to the radio, doing that is likely to mess up the alignment of the 'front-end' R.F. tuned circuits - and that may well explain some of the results you have obtained. The first R.F tuned cct. is expecting to 'see' just the right amount of inductance and capacitance as the set is tuned over its frequency range. By introducing the loop, that inductance has now changed (the amount of change largely dependent on the degree of coupling from the loop to the set), so consequently, the 'front-end' tracking will be thrown out of alignment, and that mis-alignment will be frequency-sensitive, of course.
The most effective remedy, of course, is simply to replace the broken ferrite rod.
As for sets that do not use a ferrite rod, but with an 'internal aerial', that aerial will still comprise a critical-value inductance for the first tuned cct. in the set, so the above comment is still applicable.
For valve sets that are designed for the traditional 'longwire' running down the garden, then yes, I can see that a loop (of almost any dimensions) will be beneficial to some degree, if the traditional '100-foot longwire' is not available.
HTH,
Al. / March 13, 2013 //
