Re: Bigger Loopstick for Tecsun PL 390 Series Radios

Alex P

Can't speak to the Tecsun but when I was removing the 'split' coil ferrites from japanese made pocket radios in the 1970's, discovered that the ferrite core winding does double duty for the local oscillator. The antenna part of the winding is tuned simultaneously with the LO part of the winding with the variable cap. The middle winding tap is usually at ground potential. The longer part of the winding is the antenna pickup part while the shorter winding is for the LO part operating at a higher frequency. Since both are tuned and have relatively high Q, the difference in tuned frequency is always about the same and this provides sufficient frequency separation and Q so that the LO signal is down sufficiently as to not substantially affect the antenna part.

This is an example of novel engineering cost reduction for the consumer mass market.

--- In, Jerry Popiel <jerry_popiel@...> wrote:

I have wondered the same thing Rick, ie. what would be the advantage that Tecsun's engineers see in using a single coil split into 3 sections? Also in some old radios I have from the late 1960's I have seen the same 3 separate sections on Loopstick Antenna's from a 17 Transistor Radio I have that was made in Japan.

However for Medium Wave the measured inductance I used on my external 7.5" Loopstick on my Tecsun PL380 was 550uH, and 1700uH for Longwave as per Gary's construction recommendations. Wonder if a single coil split into 3 separate sections might be even better, but I don't think there would be enough room on the big 7.5" external ferrite rod to do this??


From: Rick Robinson <w4dst@...>
Sent: Friday, May 11, 2012 9:33:01 PM
Subject: Re: [ultralightdx] Bigger Loopstick for Tecsun PL 390 Series Radios

On 5/11/2012 7:11 PM, D1028Gary@... wrote:
(single coil split into three sections) as in the Si4734
chip Ultralight radios like the PL-310, PL-380 and PL-606).
Gary or anyone else,
Is there a logical explanation for the "split 3" windings on these ferrite bars?  I took the bar out of one of my PL-380s and rewound it with a slightly larger litz wire using the same inductance but wound up with a much wider coil, roughly 75% of the length of the bar.  There is a measurable increase in signal sensitivity compared to my strictly stock PL-380.  It just seems like an odd way of winding an antenna.  


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