Message-ID: <9BC822CC8A17411A8CB629CAA5052C11@AGB>
From: "Graham" <g8fzk@g8fzk.fsnet.co.uk>
To: <rsgb_lf_group@blacksheep.org>
References: <4EAAEAEA.7030800@iup.uni-heidelberg.de> <FBF0B7FE4F7A469FA77C02CBB09C7F06@konda03bf4520e>
In-Reply-To: <FBF0B7FE4F7A469FA77C02CBB09C7F06@konda03bf4520e>
Date: Sat, 29 Oct 2011 13:02:01 +0100
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Subject: Re: LF: Re: Q measurements at DK7FC
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Interesting  link

G.

--------------------------------------------------
From: "Joze Konda - S52AB" <s52ab@siol.com>
Sent: Saturday, October 29, 2011 6:55 AM
To: <rsgb_lf_group@blacksheep.org>
Subject: LF: Re: Q measurements at DK7FC

>
> Maybe in help abouth Q calculation:
> http://hamwaves.com/antennas/inductance.html
>
> 73,Joze S52AB
>
>
>
>
> ----- Original Message -----=20
> From: "Stefan Sch=E4fer" <Stefan.Schaefer@iup.uni-heidelberg.de>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Friday, October 28, 2011 7:48 PM
> Subject: LF: Q measurements at DK7FC
>
>
>> LF,
>>
>> For those who are interested, i have a small report of my todays Decca=
 RF=20
>> litz coil measurements. Maybe this will give newcomers some ideas how =
to=20
>> proceed...
>>
>> Since i do not want to cut that wire into to many pieces, i first took=
=20
>> the fulll 170m piece to see where i come out. The calculated value is=20
>> 160m for a 3.00 mH coil. The program says that i will achieve 3,08 mH=20
>> with the actual dimensions i achieved last night after winding the wir=
e.
>>
>> I did some pre-tests a few weeks ago and measured the antenna C as=20
>> precise as possible. I put one single turn arround my (old) coil and=20
>> measured the resonance frequency by turning the wheel as long as the=20
>> highest amplitude was shown on a nearby probe, connected to a portable=
=20
>> oscilloscope. Then i replaced the antenna wire by a variable cap and=20
>> turned it to the highest amplitude peak again, without changing the=20
>> frequency and the hardware arrangement, as good as possible. I got a C=
 of=20
>> 447 pF. Resonance was found at 137.3 kHz, so i have 3.0 mH on that coi=
l.
>>
>> Today i placed the coil on the position where it will be placed later,=
 to=20
>> include the sourrounding losses in the measurement. These cannot be=20
>> avoided completely.
>>
>> Now its time to show some photos of another excellent autumn day in=20
>> finest WX conds and a good view on the top of that building where one =
can=20
>> do many individual experiments without beeing inderrupted or disturbed=
:
>> http://dl.dropbox.com/u/19882028/LF/LF%20stuff%20on%20the%20top%20of%2=
0building%2C%20euphorism%20WX.jpg
>> http://dl.dropbox.com/u/19882028/LF/Litz%20coil%20in%20final%20positio=
n.jpg
>> http://dl.dropbox.com/u/19882028/LF/Alternative%20position%20for%20Q%2=
0measurement.jpg=20
>> (Heidelberg castle in Background)
>> Sorry for the bad quality, it's a 4 year old mobile phone camera with=20
>> scratched lens...
>>
>> I found it was quite difficult to accurately measure such a high Q coi=
l.=20
>> I saw that the peak amplitude significantly decreased when i come a bi=
t=20
>> closer to the coil. Furthermore that cheap oscilloscope allows not ver=
y=20
>> accurate reading of the values. So the measurements are rather showing=
=20
>> the region where i will come out later. But very promising!
>>
>> When connecting the antenna or the variable cap to the coil, the=20
>> resonance was found near 130.2 kHz. So the wire is to long and L to hi=
gh,=20
>> better than to low! :-) If C is 447 pF, then L is about 3.35 mH, 10% t=
o=20
>> much. Probably the 6mm thick glass adds some C between the turns due t=
o=20
>> its relatively high relative permittivity of 7. But the body has to be=
=20
>> non-burning, this was the idea.
>> I did 3 Q measurements and achieved 3 Q values ;-) These are 566, 627 =
and=20
>> 734. During the 734 measurement i took care to be as far away from the=
=20
>> coil as possible. So i rather expect values arround 700+ are realistic=
,=20
>> later.
>>
>> Expecting a L of 3 mH and a Q of 750 would imply losses of  3.4 Ohm wh=
ich=20
>> is a loss reduction (compared to the old/current coil) of 60% ! BTW th=
e=20
>> DC resistance of that coil is 1.0 Ohm.
>>
>> The ratio of length to diameter is about 3, which is not ideal but mor=
e=20
>> secure regarding voltage per turn, which will be an issue.
>>
>> I expect higher Q values for the second version of that coil since:
>> -The distance of the lowest turn to ground will increase
>> -The length/diameter ration will decrease
>> -The wire length will decrease
>>
>> Enough data to fill some formulas of Rik/ON7YD's fine LF antenna web p=
age=20
>> at http://www.strobbe.eu/on7yd/136ant/
>>
>> Now I'll remove some turns to come closer to 137.0 kHz...
>>
>>
>> 73 to all the homebrewers
>>
>> Stefan/DK7FC
>>
>>
>>
>>
>> -----
>> No virus found in this message.
>> Checked by AVG - www.avg.com
>> Version: 10.0.1411 / Virus Database: 2092/3980 - Release Date: 10/28/1=
1
>>
>
>
>=20