Interesting data. One reference I found discussed the dramatic increase
in PIM from motion induced rubbing of coax braid strands, although again
unlikely an issue at HF. Thus one might suppose a bare stranded wire
dipole might generate PIM in a wind.
Grant KZ1W
On 4/24/2018 14:45 PM, Steve Maki wrote:
On 04/24/18 17:03 PM, Grant Saviers wrote:
Andrew published some research that shows the PIM (passive intermod)
differences between braid and solid copper shields for coax. I
couldn't find that pdf on the web, but it shows how braid generates
more IM products than solid Cu tubing. I think its pretty
insignificant for HF ham radio.
Mostly true. For HF it's insignificant. For UHF and above it's
insignificant for receive only or simplex. For UHF duplex (repeaters)
I *think* it can be significant. LMR style cables have very poor PIM
performance (like 25 dB worse or more) compared to Heliax/hardline
style cables. I've measured PIM on LMR400 & LMR600 at 700 MHz and
above, and it's horrendous by cell service LTE standards (which is
-143 dBc using two 20 watt carriers).
Kinda surprising given that the *RF* foil shield is solid for all (or
most) practical purposes.
-Steve K8LX
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