|
Hello all,
Thanks all for your comments, it
helps.
I can't recall that anybody would ever mention the
possibility to change serial connection of the coils of a variometer to the
parallel one.
If the ratio is about 1:4, which is still possible
to reach with the mechanically simple cylinder-in-cylinder design, the
ranges will meet each other and the overall ratio is about 1:16.
BTW there is currently a beautiful loading coil on
the eBay. Such items rarely appear there. I would buy it myself
immediatelly but unfortunatelly the seller ships the item to Germany only.
Hurry up, about one day remains and the price is still only 2 Euro!
73, Petr, OK1FIG
----- Original Message -----
Sent: Thursday, April 02, 2009 2:49
PM
Subject: Re: LF: Tune and match the ant
for 50kHz...550kHz
And, by the way, the
"sphere in sphere" variometer has a big drawback: Its Q is quite OK at
maximum inductivity but very poor at its minumum. Explanation is simple.
Just assuming the resistance of the wire being constant, at low inducitivity
the relation XL to R becomes very poor.
I agree on that. Rloss
stay more or less constant over the entire range.
With my variometer I
mearured a Q = 430 at maximum inductance (450uH), dropping to 50 at minimum
inductance (40uH).
73, Rik ON7YD - OR7T
OK?
73 Ha-Jo, DJ1ZB
"Rik Strobbe" <[email protected]>
schrieb:
- Hello Petr,
- 50-550kHz seems a "big shot".
- If you want to tune (bring to resonance) the antenna using a
variometer it would need a ratio of (550/50)^2 = 121.
- The variometer I use on 500kHz has a range of 40-450uH, thus a ratio
of 11. The variometer comes from an 500kHz marine transmitter and it would
be rather complex to build a copy (mechanical).
- Running low power you could use a parallel LC circuit. One end to the
antenna and the other end to ground. The TX is connected to a tap at the
coil, close to ground. You can tune the antenna to resonance by changing C
(variable capacitor) and match to 50 Ohm by changing taps on the coil. I
did that with success in the early days on 136kHz, but I could run only
30W power before the capacitor (plate distance 2mm) started arcing.
- Now you will need a capacitor with a ratio of 121, but that is not so
hard: most variable capacitors have a range of 20 or better and you can
put some fixed capacitors in parallel (via switches).
- 73, Rik ON7YD
- At 09:26 2/04/2009, you wrote:
- Hi all,
- I want to make a small transmatch (RX, TX up to 10
Watts, or so) to tune LW 41 m (or smaller T-ant) in the range 50 ... 550
kHz.
- I am not too good in theory... but I believe that the most efficient
system is the popular loading coil (home made variometer, and taps to
find 50 Ohms match).
- The simple variometer (cylindrical coil in another cylindrical coil)
is easy to make and works fine on 136kHz. However, it is possible to
change inductance in the range about 1:2 or 1:3 only, not much better.
Therefore the redudant inductance is too high to fetch the ant to
resonance on 550 kHz.
- Solution would be to make a more sophisticated variometer (best:
sphere in sphere) to reach the ratio 1:10 or so.
- Or, to use a different kind of network. Pi network, L network or T
network. BTW I would also prefer to use a rotary switch and solder
twenty condensers rather than to make twenty taps on a coil wound with
litz wire...
- How did you solve this yourself?
- Thanks, 73, Petr, OK1FIG
-
- Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
for more information.
Disclaimer: http://www.kuleuven.be/cwis/email_disclaimer.htm
for more information.
|
