The 820C is not a split mount but the older PTP800’s are. The systems that use a remote radio head and the LMR or other coax to feed DC to the remote head expect that the outer jacket (that they are using as a return path for the DC) will be grounded to the tower. It’s not that the radio really cares that much how it’s DC is referenced to ground - but that outer jacket of the cable (the 0V side of the -48V supply) is grounded to the tower in a number of places, including at the the antenna mount itself.
Checking the 820C I have here with a meter it appears that the +/- is not hard connected to the case. Fairly high resistance between either input and the case, but the case voltage slowly floats toward either rail when measured which indicates to me that there is some type of surge suppression in there and that you probably don’t want to do this backward. Mark > On Dec 7, 2016, at 1:58 PM, Ken Hohhof <[email protected]> wrote: > > There aren’t really +48 and -48 power supplies, other than one side being > connected to ground. It’s like the battery in your car, it isn’t a +12 or > -12 volt battery, it’s just a 12 volt battery, with (nominal) 12 volts > between + and – terminals. But the negative side is wired to chassis (in a > negative ground car), which makes the power +12 volts. Some unusual power > supplies may have one side grounded internally, likely you would only see > that on a DC-DC converter, but most power supplies are floating until you > ground one side. I think theoretically 802.3at POEs are +48V and ground, but > in actual practice many POEs and many 802.3at powered devices are agnostic > and/or floating. > > <> > From: Af [mailto:[email protected]] On Behalf Of Bill Prince > Sent: Wednesday, December 7, 2016 12:27 PM > To: [email protected] > Subject: Re: [AFMUG] WTB IP-20C POE > > FWIW, the POE injector itself should be agnostic WRT polarity. The issue > boils down to three things; (1) The polarity of the power supply, (2) The > polarity of the equipment, and (3) whether either 1 or 2 bond their > respective returns to chassis ground. > > If both the PS and the equipment isolate logic ground from chassis ground, > then -V and +V are basically a don't care. As soon as one or the other (or > both) bonds logic ground to chassis ground, then you better be paying > attention. > > I know that many/most Trango radios bond logic ground to chassis ground, and > they are -48V (or +48V return). If all other equipment on site is also -48V, > then you're probably OK. However, as soon as another piece of equipment gets > added to the site, _AND_ it is +48V, then you have a conflict. At this point, > you need to figure out how you're going to keep +48V away from the -48V. > > -bp > > > On Wednesday, December 7, 2016 10:16 AM, Mark Radabaugh <[email protected] > <mailto:[email protected]>> wrote: > > > It’s marked -48V on the power connector. I don’t think I would try floating > a ground with it to use +48. If you only have +48 a Meanwell DC/DC converter > to get -48V is a lot less expensive than the POE injector. Of course maybe > you want POE in which case it might justify the cost. > > We routinely run these with a 2x22 gauge copper + 2 fiber cable where we use > the copper as the -48V/0V and the fiber for data. We do not connect the > POE/Copper Ethernet port, or the 3rd management port. > > Mark Radabaugh > Amplex > 22690 Pemberville Rd > Luckey, OH 43443 > 419-837-5015 x1021 > 419-261-5996 (cell) > [email protected] <mailto:[email protected]> > >> On Dec 7, 2016, at 11:09 AM, Faisal Imtiaz <[email protected] >> <mailto:[email protected]>> wrote: >> >> Hi Mark, >> >> Just to make sure there this is no confusion in the 'lingo' >> >> 820C/IP20c is designed to run on -48v DC (telecom power plant), and the >> radio gets powder via the Ethernet cable (POE) >> >> The external POE Injector device is presented as a DC-DC converter.. >> The question was is this necessary when using +48vdc power source or just a >> matter of changing polarity... >> >> Regards. >> >> Faisal Imtiaz >> Snappy Internet & Telecom >> 7266 SW 48 Street >> Miami, FL 33155 >> Tel: 305 663 5518 x 232 >> >> Help-desk: (305)663-5518 Option 2 or Email: [email protected] >> <mailto:[email protected]> >> >> ----- Original Message ----- >> >>> From: "Mark Radabaugh" <[email protected] <mailto:[email protected]>> >>> To: [email protected] <mailto:[email protected]> >>> Sent: Wednesday, December 7, 2016 10:56:06 AM >>> Subject: Re: [AFMUG] WTB IP-20C POE >> >> >>> The answer to the question: >>> >>> The 820C runs perfectly fine on -48VDC run directly to the radio. >>> >>> You do not need the POE adapter unless you really want to run them using >>> POE. >>> >>> I do not explicitly know if they will run on +48VDC - I believe they will >>> but >>> have not actually tried that. >>> >>> We have quite a few running on -48VDC from Emerson and Eltek rectifier >>> shelfs. >>> >>> Mark >>> >>> >>> >>>> On Dec 7, 2016, at 10:20 AM, [email protected] <mailto:[email protected]> >>>> wrote: >>>> >>>> yes >>>> >>>> -----Original Message----- From: Faisal Imtiaz >>>> Sent: Tuesday, December 6, 2016 5:13 PM >>>> To: [email protected] <mailto:[email protected]> >>>> Subject: Re: [AFMUG] WTB IP-20C POE >>>> >>>> Hi Chuck... >>>> >>>> This may be an opportunity to clarify something... >>>> >>>> According to the specs Ceragon IP-20c is a -48vdc radio. >>>> Their POE box/adapter, takes 48v dc or 24v dc and powers the radio. >>>> >>>> There has not been any clear answer if their Radios will run on regular >>>> 48vdc >>>> directly ... >>>> There have been folks who have 'tested' the cambium 820 version of these >>>> plugging directly on the Netonix switches. >>>> >>>> In my opinion, these are not 'in-expensive' radios that I would risk >>>> installing >>>> in-correctly. >>>> >>>> In recommending your injector / surge protector as a solution, my question >>>> would >>>> be. >>>> >>>> 1) can we do -48v dc power via these devices ? it is just a matter of >>>> making >>>> sure the polarity of the dc cable is correct ? or is there more to it. >>>> >>>> >>>> Regards >>>> >>>> Faisal Imtiaz >>>> >>>> >>>> ----- Original Message ----- >>>> >>>>> From: "Chuck McCown" <[email protected] <mailto:[email protected]>> >>>>> To: [email protected] <mailto:[email protected]> >>>>> Sent: Tuesday, December 6, 2016 6:08:49 PM >>>>> Subject: Re: [AFMUG] WTB IP-20C POE >>>> >>>> >>>>> I am hurt... >>>>> >>>>> http://www.mccowntech.com/800-gige-poe-outdoor-midspan-poe-injector-ethernet-surge-protector/ >>>>> >>>>> <http://www.mccowntech.com/800-gige-poe-outdoor-midspan-poe-injector-ethernet-surge-protector/> >>>>> http://www.mccowntech.com/800-gige-poe-apc-rack-mount-surge-protector-power-inserter/ >>>>> >>>>> <http://www.mccowntech.com/800-gige-poe-apc-rack-mount-surge-protector-power-inserter/> >>>>> >>>>> Sheesh! >>>>> >>>>> -----Original Message----- >>>>> From: Faisal Imtiaz >>>>> Sent: Tuesday, December 06, 2016 3:55 PM >>>>> To: [email protected] <mailto:[email protected]> >>>>> Subject: Re: [AFMUG] WTB IP-20C POE >>>>> >>>>> Some suggestions:- >>>>> >>>>> for the POE injector... >>>>> you can try a Cambium Reseller. >>>>> you can possibly by them on Ebay (shipping from Israel) >>>>> you can try Surplus Wireless Gear folks too. >>>>> >>>>> In regards to the Power Supply, that is a straight forward 48v DC power >>>>> supply (Brick). >>>>> >>>>> Regards >>>>> >>>>> >>>>> Faisal Imtiaz >>>>> Snappy Internet & Telecom >>>>> 7266 SW 48 Street >>>>> Miami, FL 33155 >>>>> Tel: 305 663 5518 x 232 >>>>> >>>>> Help-desk: (305)663-5518 Option 2 or Email: [email protected] >>>>> <mailto:[email protected]> >>>>> >>>>> ----- Original Message ----- >>>>> >>>>>> From: "Sterling Jacobson" <[email protected] >>>>>> <mailto:[email protected]>> >>>>>> To: "[email protected] <mailto:[email protected]>" <[email protected] >>>>>> <mailto:[email protected]>> >>>>>> Sent: Tuesday, December 6, 2016 5:45:19 PM >>>>>> Subject: [AFMUG] WTB IP-20C POE >>>>> >>>>> >>>>>> Somehow I misplaced my Ceragon POE injector and power supplies during a >>>>>> cabinet >>>>>> move. >>>>>> >>>>>> Anyone happen to have a Ceragon IP-20C compatible POE unit they could >>>>>> sell >>>>>> me? >>>>>> >>>>>> I think the power supplies probably aren't that hard to find, but the POE >>>>>> apparently is. > > > >
