Re: Coupling a T2FD to a S350DL
- From: No Spam <no@xxxxxxxx>
- Date: Wed, 27 Aug 2008 00:37:40 -0500
On Tue, 26 Aug 2008 22:19:42 +0100, Bubblesdee wrote:
Hi
I am new to this forum and have a (most likely) dumb question
I recently aquired a S350DL receiver. I will be using this rig until I
can buy a rela communications receiver. I will be using it to receive
Shortwave only. I have constructed a T2FD (Tilted, terminated, folded
dipole) with a design feed point impedance of 300 ohms. The S350 DL
only has an unbalance high impedance external antenna point and a ground
on it. How can I attach the T2Fd to the S350Dl and acheive a good
impedance match.
1) Is the whip antenna on the S350DL a low impedance feed point (i.e. 50
or 75 ohms)? If so, could I use a 4:1 balun at the feedpoint of the
T2FD to convert the feed line to 75 ohm coax (which would be unbalance
line now) and just clip the center conductor to the whip and the sheild
to a grounding rod?
2) I could use 300 ohm ladder line to connect to the T2FD but the
problem is that the S350DL does not have a balanced esternal input point
on it.
I guess what I am asking is what would be the best way to couple A 300
ohm T2FD antenna to a Crappy Radioshack S350DL receiver and achieve
reasonable impedance matching.
On HF, matching imp for receiving should not make much difference give-or-
take a few 100%
I suspect whip antenna is high imp. ~2k and unbalanced. You would need
to make a one2one or four2one matching xformer placed near the radio with
ladder line coming from antenna. This will stop common mode noise from
entering your radio via feedline. Two 300->75 ohm TV xformers back to
back should work.
twinlead 300 xformer 75 short coax 75 -> 300 twinlead
gator clip the xformer output to your collapsed whip
antenna and ear jack ground.
If you get allot of intermod from front end overload, place some
resistors between between whip and ear jack ground.
.
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