In that case, my suggestion is think of them all as transmission lines
in coax. terminate as needed.
Others here will also have points I have missed I am sure, or
alternative equally valid suggestions.
beign critical (maybe I am being over critical) :
watch out also for reflections from unterminated (open ) relay contacts,
the 2x pulse you might get back at the driver might cause harm or
trouble on the supply rail.
IE so source terminate ideally, even if it costs you a little swing or
at least a little series R like 10 ohms source R to mop up reflections
back on the source... if its swinging 2V with source term = 10 ohms into
51 ohms, that wont hurt too much.
rather than just totem pole strong CMOS driver , consider LVPECL style
driving, also.
IE it depends what drivers and receivers you choose.... simple would be
all 1.8V CMOS I guess, most stronger buffers will drive 50 ohms and 1.8V
if you plan on multiple drop, then you'll need to consider where you
place the termination... which is why differential rocks over single
ended because the swing can drop before the trouble develops with double
termination. of course if you AC couple into single ended setups that
can work but messy.
glen
On 7/07/2019 2:07 PM, Taka Kamiya via time-nuts wrote:
I should have mentioned this clearly earlier, but all converting and switching,
then measuring happens in ONE 2U rack case. Length of each cable is minimal.
I thought mention of TICC would make it sort of clear but it didn't.
I have LOTS of coax relays. I'll use them. It's a gross overkill but I've
seen 80s HP equipment have overly generous parts selections, too. It's hard to
explain EXACTLY as the contraption isn't built yet. That made it necessary to
use generic terms. I apologize for causing confusion.
---------------------------------------
(Mr.) Taka Kamiya
KB4EMF / ex JF2DKG
On Sunday, July 7, 2019, 12:00:52 AM EDT, Glen English VK1XX
<glenl...@pacificmedia.com.au> wrote:
Hal, Good point.
and I have never seen a spec for phase stability for Cat-7 cable !
for RG58, OR OTHER polyethylene, might be up to 150ppm /deg C. maybe as
good as 10 ppm/deg C for some LMR.
With 1000 feet of cable might be an issue for fine stuff. a few nano
seconds each way over temperature might not matter for his project...
I forget it is not a microwave RF VNA application. Easy to resolve
anyway with a difference balance term somewhere.
g
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