Hello Marcus,

could the loss in the impedance transformer be avoided by tapping the loading coil ?
I just had a look at the "copper wire tables" and 0.2mm OD wire (actually 0.15mm copper) has a resistance of 1 Ohm/m. Quite a  challenge to get 830m wire on the coil without breaking the wire :-).
Would it also work with less (but thicker) wire and a ferrite core ?
The ferrite core will introduce some additional loss, but on the other hand you will have less (and thicker) wire reducing the copper losses. But I am not sure what the overall effect will be.

73, Rik  ON7YD


At 11:44 8/03/2010, you wrote:

Dear Rik, LF,
 
yes these numbers are pretty much where I arrived in my calculations. There is some loss in the transformer, about  1024* 0.25 ohm from the primary and 60 ohm in the secondary, adding up to 315 ohm series loss. Thus antenna resistance at 9 kHz would be more like 700 ohm. The same antenna has a much lower resistance on 137 kHz, around 35 ohms normally, and down to 28 ohms in cold and dry weather. This includes the LF coil resistance (RF litz wire, Q ~ 700, Rcoil ~ 7 ohm). The large difference indicates that capacitively coupled losses from high-resistance objects (trees, roof etc.) are probably dominating at 9 kHz.
 
BTW I just noticed an error in the the 9 kHz coil description, it actually has 10 sections, 500 turns each (back to kindergarten then to learn counting to ten ;-). Skin effect is probably still neglegible with the thin 0.2 mm wire, but there may be some eddy current loss (proximity effect) in the overlapping layers.

Best 73,
Markus


-----Urspruengliche Mitteilung-----
Von: Rik Strobbe <[email protected]>
An: [email protected] <[email protected]>
Verschickt: Mo., 8. Mrz. 2010, 9:22
Thema: Re: LF: 12 km on Dream(ers) Band

Hello Marcus,

first of all congrats with your achievement.
Based on the numbers you gave I tried to figure out the loss resistance at 9kHz:
- 35W and 0.135A would give 1920 Ohm.
- with a 32/1 transformer the TX (audio amp) would be loaded with 1.8 Ohm
Assuming that the loss at 9kHz is slightly more than the DC loss (let's say 900 Ohm) the "ground loss" (including greenery and buildings) would be about 1 kOhm.
Can you confirm this figures ?

73, Rik  ON7YD