Re: Gary et al- ferrite question-FARMERIK
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Hello Farmerik,
<<< I know Gary is an expert on adding larger ferrite antennas outside the cases of ULR's, so I thought I'd ask about improving Hi-Fi AM tuners the same way. One of my sets has leads from the ferrite loop stick long enough to mount it on top of the case instead of mostly inside the back of a metal case where it must be shielded. Then the loop stick could be rotated to pick up in different directions. >>>
Many of the vintage Hi-Fi tuners (and receivers) from the 60's and 70's already have the AM loopstick mounted outside the chassis on a swivel base-- usually attached to the back of the cabinet. Any time that you can get a loopstick outside a radio's cabinet, you can probably improve its MW reception. But to be honest, even mounting an external 7.5" loopstick on a swivel base outside your Hi-Fi tuner is highly unlikely to make the model a DXing champion, Farmerik.
Any large metal conductors in the immediate vicinity of a loopstick will degrade its RF performance, and the huge Hi-Fi chassis is an obvious example. High-performance 7.5" loopsticks work extremely well when mounted outside of plastic-case Ultralight radios, but well-shielded table receivers always have some serious metallic components, and depend on large external antennas (of the proper impedance) for serious weak-signal reception. Loopsticks really don't fit this job description, although most of the vintage Hi-Fi manufacturers included them because they were relatively cheap, convenient, and better than nothing. Serious MW-DXers of that vintage period would use table receivers with large, externally mounted antennas of the proper impedance.
73, Gary DeBock (in Puyallup, WA, USA)
-----Original Message----- From: farmerik@... [ultralightdx] To: ultralightdx Sent: Wed, Feb 4, 2015 12:43 pm Subject: [ultralightdx] Gary et al- ferrite question-FARMERIK I know Gary is an expert on adding larger ferrite antennas outside the cases of ULR's, so I thought I'd ask about improving Hi-Fi AM tuners the same way. One of my sets has leads from the ferrite loop stick long enough to mount it on top of the case instead of mostly inside the back of a metal case where it must be shielded. Then the loop stick could be rotated to pick up in different directions. There are only two wires/one winding on the loop stick which is tuned by a section of the variable tuning cap and connects to the RF amp tube. There are also screw connections for an external AM antenna and ground. The external antenna screw has a fixed cap on either side of where the tuned loop stick circuit connects between the tube and antenna screw. I REALLY do not understand radio theory. So my questions are would a short winding on the loop stick likely be a better way to connect an external antenna and prevent it from picking up other signals or noise? < br>
Also, how could I shield the loop stick very well so only the external antenna feeds in signals? My guess is steel/iron would interact with the magnetic field, not just shield the coil. I am thinking something like an IF shield can, but it may be a loaf baking pan I can set over the ferrite antenna and connect with a ground wire to the chassis. I have no fabrication skills, it has to be very simple. -FARMERIK |
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