Re: BL2 w/Multi-Band Dipole

Posted by Mike K8CN on Apr 02, 2012; 6:00pm
URL: http://elecraft.85.s1.nabble.com/BL2-w-Multi-Band-Dipole-tp7429655p7430371.html

Hi David,

An 18 inch jumper cable won't produce a dramatic shift in feedpoint impedance over that presented by a direct connection (via a double male BNC) to the K1/K2 ATU even on 10 meters.  If an adequate SWR can be obtained by the ATU (VSWR less than 2.0) with the coax jumper in place on the bands of interest (you may need to try the two different balun ratios), you can be happy.

If you want to see the possible difference in the impedances presented to the ATU for any given impedance at the BL2 BNC connector, the TLW program, written by Dean, N6BV and supplied with recent editions of the ARRL Antenna Book, will calculate for you the transformed impedance at the end of an arbitrary length of feedline.  It's not necessary in your practical situation, but it is interesting and educational if you've not worked much with feedlines.

The only concern with the direct connection is the case when there may be repetitive movement of the 450 ohm window/ladder line; you'll want to have some separate strain relief to prevent repeated flexure of the BNC female connector.  The ATU connectors on my K2 are well-secured to the case, but the connector bodies are plastic.  For an indoor shack environment you should have no problem either way.

73,
Mike, K8CN