Many thanks to SWLing Post contributor, Rolf, who writes:
I made a great discovery tuning using a second passive analog radio.
When I tune to Radio Caroline, for example, on my portable I can receive the signal okay. When I put the receiving radio on minimum then place it next to and couple it with the second radio, it is receiving a lot better!
Even stations I could hardly hear, now i can hear them!
Check out my short demonstration video:
Click here to view on YouTube.
That is fascinating, Rolf. Thank you for sharing. Indeed, this is one of the reasons why I try to maintain a good distance between radios when comparing them in reviews. In this case, though, you’re using coupling to your advantage!
I use a second receiver to act as a BFO to hear SSB and CW signal and I have noticed that many AM stations will come in cleaner! I did not focus on this so a good find indeed! It may be some what like the Barlow Wadley radios of the 1960s using the Wadley Loop to lock into the frequency!
73 Rod W8GRI
> “It may be some what like the Barlow Wadley radios of the 1960s using the Wadley Loop to lock into the frequency!”
What you noticed may be more like an old-fashioned “Q multiplier” i.e. regen.
What Rolf’s shown is passive (the video title indicates the second radio is off), so more like a coupled preselector; the tuned circuit (antenna winding plus tuning cap) in the unpowered radio is still resonant, and when placed nearby couples that signal to the active radio. Much the same as the post the other week showing how putting a portable radio inside a tuned loop antenna boosts the signal. It’s a neat trick, albeit one that’s older tham I am, but it still manages to amaze – google “Ferrite Antenna Booster” or similar.