The 15m Stack and Fixed Beams

5-5-5 on 15m - plus 5 elements fixed on SA 


The 15m station antennas are as follows - controlled by a stack switch, directed by the Microham SMD in the shack:



Top: rotating 15m JK155 5-element/36 foot yagi at 116'

Mid High: fixed-on-EU 15m JK155 5-element/36 foot yagi at 92'

Mid Low:  fixed-on-EU 15m JK155 5-element/36 foot yagi at 68'  

Bot:  fixed-on-SA 15m reworked KLM 5-element/36 foot yagi at 54'


Shown below is the JK155 assembled and awaiting truss hardware attachment.




The N0XA KLM 15m Rebuild


The 15m KLM 15M6 "Big Sticker" beam has literally worked 'em all when sitting atop a tower at N0XA (SK).  I'm not sure how long it was up at Freds - around 30 years is a pretty good guess.  He had it mounted at about 80', just below a 10m KLM of the same series.  Both beams are in use here at my station although I've taken the liberty of rebuilding the beams along modern OWA themes.

Initially I had planned on using the KLM as the fixed-on-EU mid stack beam but in the end decided to move it down to serve the fixed-on-SA role.  

The KLM was originally a 6-element design with KLM's funky 200-ohm feedpoint dual driven element layout that I never could quite understand.  And because I would be matching it up with the JK155, I rebuilt the KLM to pretty closely match the JK electrically - not difficult given they have the same boom length.  



The finished KLM rebuild below.  Awaiting only feedline prior to moving to the tower.



Hope some of that N0XA magic rubs off these old KLMs and helps me work the world as well!


Model Predictions



The EZNEC model with the 3-high stack looks like this.  Peak gain is a bit over 19 dBi with a nice top and rear pattern.  The 2nd primary lobe falls at about 21 degrees.




















HFTA Analysis

Beaming to EU in a fixed stack (BLUE) has a pretty good plot with almost 20 dBi of gain at the peak.  Most of the EU signals are going to come in a angles a bit lower but the stack gain is still good as the TOA drops.  Top-2 (RED) and bottom-2 (GREEN) are some of the other options available for switching by the operator and would help if you happen to be trying to work a close in guy who's down in the null.



JA, like other bands, suffers greatly from the terrain problem off to the NW as reflected by the flat ground (RED) plot below.  Notice how the actual top rotating antenna suffers by as much as 5 dB due to the land topology alone, only catching up to parity at about 8 degrees and above.



A single antenna mounted at 54' is set on SA and is adequate to the task.
























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