Re: [IRCA] Longwire for Tecsun PL-360

[Lostgallifreyan <z.crow@xxxxxxxxxxxxxx>]

About that, some new info I got just now..
I tested my toroid coil using a Fluke 79 Series II meter, not true RMS but I'm after relative voltage at fixed frequency sine wave, not absolute voltage, so this should be fine. Also, a Chinese digital phase accumulator based signal generator, sinewave, digital readout and variable output amplitude (amazing widget for the price). It fed through R, through L, to ground, with results as follows:
99.7R
2.506VAC across R and L
1.253VAC across L
Frequency is 21.57 KHz, so by L=R/(2*PI*F*3^0.5), inductance is 4.247E-4 H, or 424.7 µH.

A bit high, should be 350 µH, but the reception result seemed to indicate that it was too low, not too high. If anyone can help me understand why this results in such poor tuning selectivity, please do. I'd assumed all I had to do was satisfy the PL-360's inductance needs, then couple the longwire into that. It certainly works with the existing antenna.

For reference, a test of the supplied external ferrite rod antenna:
99.7R
2.507VAC across R and L
1.253VAC across L
Frequency is 29.2 KHz, so by L=R/(2*PI*F*3^0.5), inductance is 3.137E-4 H, or 313.7 µH.

Slightly less than the expected 350 µH, but not the starved minimum that one web page reported, of only 240 or so, but I think that was about the PL-380's ferrite antenna, not PL-360's. Same radio IC though, so likely relevant.

I'm wondering if the inductance range is more critical for the Si4734 or Si4735 IC than I thought it was, or if winding the toroid's coil with turns closely set or using Litz wire is better in this case. I used single strand enameled copper, about 0.6mm diameter. I'm also wondering if my assumption that a 1:1 turns ratio is entirely wrong, but given successful results on a PL-390 with about 80 turns and about 65 on their main winding, it doesn't look like it can be bad enough to explain the poor reults with my toroid. (Which is presumably around 4000 to 5000 permeability, as the seller claimed after doing his own tests before listing them, and judging by today's test it's one of the higher ones in the batch I bought...)

Crow.


Lostgallifreyan <z.crow@xxxxxxxxxxxxxx> wrote:
(04/09/2015 16:45)

>To my question... Can I get good results using a small ferrite toroid (about an inch, permeability allegedly around 5000 to 5000) to satisfy the PL-360's need for about 350µH of inductance to tune on AM while dramatically reducing local EMI leaking into the doings?
>
>The idea seems good in concept, but I have trouble with it so far. I calculated (using three online sources to check with first) that 11 turns spaced around most of the toroid should get the required inductance on this core. I wound a bifilar winding, 1:1, so the other one got the longwire to ground.. I found that selectivity was almost as poor as if I tried plugging the wire straignt to the socket leaving the radio with no inductance fit to tune with. :) This happened whether I commoned the two ground ends or not. I'm fairly sure the wire didn't get scraped and shorted though the ferrite, so I don't think that's why...
>
>My next move is to try to measure the inductance by a half-volt method for calulation with a method I researched yesterday, to see if I'm getting a wildly wrong result out of that toroid, but I also think askign here is a good idea.
>
>Crow.

_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca

Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers

For more information: http://www.ircaonline.org

To Post a message: irca@xxxxxxxxxxxxxxxx