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From: k2ors@comcast.net (Warren K2ORS/WD2XGJ)
To:  rsgb_lf_group@blacksheep.org (rsgb lf reflector)
Cc: lowfer@lwca.org (LWCA LF Reflector)
Date: Fri, 02 Jun 2006 02:55:55 +0000
Message-Id: <060220060255.15250.447FA8BB0002A5A600003B9222007348300B97010D0A020E06979D0E03@comcast.net>
Subject: LF: Transformer problem; advice sought
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Status: O

Hello the list,

   I have been experiencing heating problems with my step-down toroidal transformer that feeds my transmit loop. Fearing core saturaton issues I have been going to ever larger cores and more and more turns in an attempt to reduce the flux density.  My latest core is 4 stacked 4" diameter Mix 78 toroids weighing a total of 3 pounds (1.34 Kg) with 28 turns of #10 on the 50 ohm winding and 5 turns of 16 mm2 wire on the loop side.

 Now for the puzzle: As suggested by J.B., I hooked two transformers back to back ; the present transformer (described above) and the previous model (4 stacked FT-290-77 toroids with 17 turns on the 50 ohm side and 3 turns on the loop side.  I connected the two transfomers with the the loop windings from one going into the loop winding of the next. One transformer 50 ohm winding was hooked to a 50 ohm Bird Dummy Load, the other transformer's 50 ohm winding went to an AEA VIA impedance bridge.  Much to my surprise I had a high swr and reactance !!!
The swr was on the order of 2.7:1 and the reactance was 45-55 ohm and increasing with frequency.

 Any thoughts on why I should show a reactive component when one transformer went directly to a 50 ohm load?


--
73 Warren K2ORS/WD2XGJ
FN42hi
http://www.w4dex.com/wd2xgj.htm