Can I derive 18V for an LNB from a 24v SMPS via a linear regulator??

[Basil]

My gear is in a weatherproof box by my dish, the SG Labs PA is powered from a SMPS variable voltage boost converter running off 12V DC to the box. At the moment the PA is running on about 20V but can run up to28V DC Can I use a linear regulator to derive an 18V supply for one LNB output polarisation from this boost converter, or might it cause noise, being switch mode? Other worry is if taking the opposite polarisation direct from the incoming 12V DC could cause any sort of voltage loop inside the LNB? The linear regulator should prevent that, shouldn't it?? Hmmm.... Thanks.

[radiogareth]

I built myself a dual LNB 'portable unit' for running in the field/shack etc with H/V switching. I used a eBay step-up SMPSU and it did indeed add some noise visible on the NB spectrum. Additional inductance and capacitance on the output cured that problem. Yours will be the other way round but should respond to further filtering if you see a difference. You could rotate the LNB so the 'noisy way round' is for WB if the noise is an issue for you on NB.
Earth loops etc don't seem to trouble LNB operation, so long as all your grounds are common you should be OK.
Gareth

[Basil]

Thanks for the speedy reply Gareth. I have got the jitters about my idea now. I have a spare boost converter, the same as the one in the box. The input ground isn't tied directly to the output ground. The negative output of the boost converter is tied to the ground plane via a resistor, either one or ten Ohm, I forget. If my 12V DC supply to the outside box is taken direct to one LNB port via a DC injector board, and the another LNB port gets 18V from another injector board via my boost converter's 22v DC and a linear 18V regulator, I think I am effectively bypassing the resistor in the ground of the boost converter's output. It seems messy with potential (excuse the pun) issues....

My other idea is to modify my MiniTioune to take one of the BATC LNB current limiting boards. If I keep the MiniTioune connected could this enable me to have DATV RX from one LNB port seeing 18V and have the other fed 12V DC from the MiniTioune, for narrow band SSB RX? The downside here of course is i I want to run my Portsdown as DATV RX or my Pluto SDR for SSB RX / TX. I think I would need a splitter in the LNB coaxes to the MiniTioune box with associated losses?

This seemingly simple problem is taking up a lot of my thought time I am wondering if I should just run a separate 18V feed to the outside box from the shack and be done with it...

Ideas VERY welcome please.