Quote:
Originally Posted by No Spam
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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Thanks for your reply No Spam.
I was wondering if you might be able to clarify some points that you made.
1) Since I will be feeding the antenna via 300 ohm feedline, transforming it down to 75 ohms (coax) to eliminate noise and then transforming it back to 300 ohms, could I not just take one leg of the output of the transformer and connect it to the External antenna connector on the back of the radio instead of the whip? and then connect the other leg from the transformer to the ear jack ground. and then finally ground the radio via the GROUND connecter on the back of the set.
2) when you refer to to the ear jack ground, are you referring to the ground of the headphone jack. Is this the same point as the GROUND connector on the back of the radio or are the two points different?
Thanks again