[TowerTalk] Grounding with LNAs half-way between the antenna and shack

[Andrew J. Buckler (BBMSC)]

Hello,
It is with some trepidation that I ask a grounding question, as I know there are many aspects. But I've seen very useful feedback for other people posting inquiries, so here goes. Forgive any infractions inherent in my proposed setup! The point is to learn so as to make it the best it can be.

I am setting up the following design:

1.     Cross-polarized EME yagi's at 60' from antennas to foundation entrance, with heliax from antenna to a box with LNAs (SSB electronics) for each polarization, T/R switching, and the connector junction from the heliax on one side and LMR400 on the other side. (Note: I am aware that often the LNAs are tower mounted. Bill of InnovAntennas suggests that it is a good tradeoff to have the LNAs more accessible, as long as there is < .5db in front of them, which is why I am using the heliax).

2.     Then, a relatively tortuous 40' of LMR400 for each receive polarization (to the matched receivers, LinkRF) as well as one for the transmit (to the linear, homebrew using W6PQL design). For configurability of the various equipment, the LMR400s will end in a connector plate on the main plate (bonded to it).

3.     Intention is to run a ground braid along with the LMR400s to bond the LNA box to the shack's single point ground plate, which is copper and bonded to the load center and with all shack equipment running to it.

4.     As such, there are two opportunities to ground the outer conductor of the feedlines; one at the shack single point ground plate, and another at the LNA box.

5.     I will also have feedlines for other bands as well as the az-el rotor cabling following the same course.

My questions:

a.     Should I use PolyPhasers, and if so, at the LNA box or at the shack ground plate? (with the other using simpler bulkhead feedthroughs bolted into holes).

b.    Do I need the extra braid mentioned in step 3 above, or does it suffice that the LMR400 braids are already doing that?

Please be gentle! I'm asking to learn.

Best regards,
Andy, K2OP
-------------------------------------
Andrew J. Buckler, Principal
BBMSC
225 Main Street, Suite 15 | Wenham, MA  01984  USA
Office: +1-978-468-0508
Fax: +1-978-468-0527
andrew.buckler at bbmsc.com<mailto:andrew.buckler at bbmsc.com> | www.bbmsc.com<http://www.bbmsc.com/>

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