CM-7777 / 7778: "New & Improved"? - Page 5 - AVS Forum | Home Theater Discussions And Reviews
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Old 10-15-2014, 12:56 AM
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As mentioned, the biggest and best combo antennas for High VHF and UHF are the Winegard 7698 and the Antennacraft HBU-55. In the large all band category, there is the Winegard 8200, Channel Master 3671 or 3020, and the Antennacraft 1850 or C490. But as said, you do not need Low VHF, so the large all band antenna is unnecessary. As for UHF, the best fringe antennas are the 91XG from Antennas Direct, Winegard 9095, Antennacraft MXU59, or possibly any of the DB8 versions. And there is also a triple boom yagi from MCM/Stellar Labs that is somewhat modeled after tthe Televes DAT75. But in your case, I would go with the 7698 Winegard, although at 50 miles even the 7696 or HBU-33 from Antennacraft should work. But I would probably choose Winegard because the build quality should better withstand winter weather conditions.
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Old 10-16-2014, 01:02 PM
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Thanks a Bunch
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Old 02-11-2015, 08:58 PM
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A Original version of the CM 7777 is for sale here for anyone interested in the lower noise figure 2.0db and two inputs. From 2011-2012. http://www.ebay.com/itm/Channel-Mast...item3aa290df0e

Thanks.
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Old 02-12-2015, 03:34 AM
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The older ones were never as low a noise figure as advertised.
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Old 02-28-2015, 07:36 AM
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Ugh. Think my "old style" 7777 has bitten the dust. Power making it up coax fine, but signals shot. Opened up preamp, and looks like a singe on the board.

Trying an RCA TVPRAMP1R in its placeClick image for larger version

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Old 03-13-2015, 05:46 AM
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FWIW, the RCA is giving me significantly better results than my "old" 7777!

I'm getting WRNN reasonably reliably from my attic-mounted "old" 4228 antenna: http://www.tvfool.com/?option=com_wr...f1f0b6314f3dbb. Never even got a sniff with the 7777.

Also seems to be handling overload better (not perfect) from WEDW, but at < 3 miles from transmitter, and above transmitter ground level, that's to be expected.

For ~$20, I'm impressed! The housing is cheapo, but this is attic-mounted, so not really a concern.
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Old 03-13-2015, 09:48 AM
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Quote:
Originally Posted by hancox View Post
FWIW, the RCA is giving me significantly better results than my "old" 7777!

I'm getting WRNN reasonably reliably from my attic-mounted "old" 4228 antenna: http://www.tvfool.com/?option=com_wr...f1f0b6314f3dbb. Never even got a sniff with the 7777.

Also seems to be handling overload better (not perfect) from WEDW, but at < 3 miles from transmitter, and above transmitter ground level, that's to be expected.

For ~$20, I'm impressed! The housing is cheapo, but this is attic-mounted, so not really a concern.
I am impressed as well. I have it hooked up to my set up, and I am 8.9 miles from the transmitters in town. We like to watch out of market channels because they have different sub channels. Also, we can get CBC (and even French CBC!) from time to time so we get some non-American programming. Those transmitters are very weak and 80-100 miles away. Of course, much of that distance is over open water.
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Old 03-18-2015, 04:33 AM
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I'm using an original version of the CM7777. I have an RCA ANT751 installed on the roof. I always got excellent results and the amp really helped with my weaker stations. Lately I've been losing 3 of my weaker channels that were always very consistent. Here's my question: Can these amps lose efficiency and be weaker over time or is it an "all or nothing" situation?
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Old 03-18-2015, 07:07 AM
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Quote:
Originally Posted by JoeWS View Post
I'm using an original version of the CM7777. I have an RCA ANT751 installed on the roof. I always got excellent results and the amp really helped with my weaker stations. Lately I've been losing 3 of my weaker channels that were always very consistent. Here's my question: Can these amps lose efficiency and be weaker over time or is it an "all or nothing" situation?

They don't gradually degrade over time. It's possible, although rare to have a partial failure. I had a Winegard HDP269 where the gain dropped to 2 dB and the noise figure went up to 10 dB. I think a nearby lightning strike partially zapped it. Unless you have a way to test it, the only way to find out is to replace it. If the problem has slowly gotten worse it could be trees that have grown over time.
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Old 03-28-2015, 01:44 PM
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Is there a way to tell when loss of a particular channel is due to the pre-amp causing overload? Do you get the "No Signal" message" or some other indication?
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Old 03-28-2015, 04:47 PM
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The tuner can't tell the difference between the decodability of a distorted signal due to overload or from a weak or multipath-impaired signal beyond a certain point. All it knows is that it cannot make heads or tails out of it. After that, it depends on the tuner's manufacturer as to what happens next.
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Old 03-28-2015, 06:20 PM
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Overload, a signal that is too weak, a high noise level that reduces SNR, and multipath reflections call all cause an increase in errors.

It is the job of the FEC (Forward Error Correction) to correct those errors, but its ability is limited. Once that limit is exceeded the signal can no longer be decoded. You then have reached the "Digital Cliff" where bad things happen, like pixelation, picture freeze, and finally dropout

It is called the Digital Cliff because the loss of signal is rather sudden as compared to analog signals that slowly get more snowy as they weaken.

Interestingly, if it weren't for the FEC, the digital signal would also degrade slowly as it weakens. It is the FEC limit that causes the sudden loss.



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Old 04-03-2016, 09:59 AM
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It appears there are a large quantity of customer returns on this item, as over 300+ units have sold on their Ebay store. I think this is so, as people purchase these and are over-driving them and they shut down not displaying channels and then returned.

I think we will see this line of pre-amps replaced with units having LTE filtering. I purchased one of these on Ebay adding it to my arsenal of products in case of future usage.

I still have a couple of Vintage CM Pre-Amps in the need of a replacement. I am encouraging hoarding. :-)

http://jmp.sh/b/XdxUMZcNJZv6WHV5KQDN
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Old 04-03-2016, 12:15 PM
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Preamp "Overload" actually means that Very Strong Input Signals are generating Third Order Intermod Products that exceed the Thermal Noise Floor, which can DESENSITIZE certain Channel Frequencies. If there are only TWO Very Strong Input Signals (e.g. Ch42 and Ch49 cited above....and can ignore other signals that are lower by 6 dB or more...esp. since ATTIC location), the Intermod Distortion (IMD) ONLY fall on top of Ch56 (now in LTE Band) and hence would Desensitize ONLY that Channel. Unless higher order (e.g. 5th Order) Intermods....or Intermods from the lower Power Level Channels are causing problem, I'm going to guesstimate that "Overload" from TV Signals is PROBABLY not a problem in your location.

However there are EIGHT Extremely to Very Strong FM Stations that could prevent reception of Hi-VHF Channels (except Very Strong Ch10)....and although unlikely, the strongest ones MIGHT also be affecting UHF Band Reception:
http://www.fmfool.com/modeling/tmp/b...d/Radar-FM.png
So I would recommend using an FM FULL BAND FILTER (aka FM Trap) on the Output of the Hi-VHF Antenna from either Antennas-Direct or MCM.

With MORE than TWO Very Strong Input Signals, the number of affected channels goes up exponentially....I prepared a General Purpose Spread Sheet Calculator where you can enter the Channel Numbers and it will Calculate the Operating Frequencies...which THEN need to be Entered into the Actual Intermod Calculator:
http://imageevent.com/holl_ands/file...=0&w=1&s=0&z=4

To VERIFY and FIX "Overload" situations, I recommend inserting a SMALL (2-6 dB) amount of Attenuation on the Input of the Preamp (spare 2-Way Splitter would be about 4 dB Loss). Third Order IMD is reduced by 3 dB for every 1 dB of Attenuation...hence 4 dB Loss reduces IMD by 12 dB....a Net improvement in SNR of 8 dB on the affected Channel. For Outdoor Installations, you should use weatherproof Attenuators, such as:
http://www.amazon.com/Parts-Express-.../dp/B0002ZPIUU

BTW: We must have said it a thousand times already: HIGH-GAIN Preamps, like CM7777 and RCA TVPRAMP1 are NOT suitable when you have VERY HIGH Input Signal Levels...they are intended for RURAL Locations. In High Signal Level Areas (which is MOST of us), a LOW-GAIN Preamp would be better, such as known High Overload Resistant A-D Juice, CM7778 or W-G HDP-269.....or CM-3410 DistroAmp located Indoors, where the small amount of Input Coax Loss actually HELPS to prevent "Overload".

Last edited by holl_ands; 04-03-2016 at 01:00 PM.
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Old 04-04-2016, 04:35 AM
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Quote:
Originally Posted by PCTools View Post
It appears there are a large quantity of customer returns on this item, as over 300+ units have sold on their Ebay store. I think this is so, as people purchase these and are over-driving them and they shut down not displaying channels and then returned.

I think we will see this line of pre-amps replaced with units having LTE filtering. I purchased one of these on Ebay adding it to my arsenal of products in case of future usage.

I still have a couple of Vintage CM Pre-Amps in the need of a replacement. I am encouraging hoarding. :-)

http://jmp.sh/b/XdxUMZcNJZv6WHV5KQDN
I think the main issue with the newer CM-7777 is that it is way too powerful for most applications at 30db gain, and it overloads and disrupts reception. So most folks return when they just should have ordered the 7778 with 16db gain instead.

But now Channel Master has just released yet another new 7777-HD preamp Amplify, with adjustable gain. It may be replacing the current versions, but is a bit pricey at $89.
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Old 04-04-2016, 04:55 AM
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To call the 7777 Amplify a "preamplifier" is a bit of a stretch since it cannot be mast-mounted at the antenna. Its only mounting provision is the set of tabs that allow it to be screwed to a flat surface. Under an eave or in an attic nearby is as close to the antenna as it's going to get.

You'd probably do far better to simply use a CM3410 and a power inserter, all of which can be bought on Amazon for about $30.
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Old 04-04-2016, 05:54 AM
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Quote:
Originally Posted by ProjectSHO89 View Post
To call the 7777 Amplify a "preamplifier" is a bit of a stretch since it cannot be mast-mounted at the antenna. Its only mounting provision is the set of tabs that allow it to be screwed to a flat surface. Under an eave or in an attic nearby is as close to the antenna as it's going to get.

You'd probably do far better to simply use a CM3410 and a power inserter, all of which can be bought on Amazon for about $30.
,

Well the Amplify is reportedly designed to function as both an inline amp inside, or an outside preamp. It comes with an optional power inserter. But I agree the CM3410 with the power inserter should perform well and is much more reasonably priced.
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Old 04-04-2016, 07:54 AM
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Quote:
Originally Posted by ProjectSHO89 View Post
You'd probably do far better to simply use a CM3410 and a power inserter, all of which can be bought on Amazon for about $30.

Quote:
Originally Posted by tylerSC View Post
,

But I agree the CM3410 with the power inserter should perform well and is much more reasonably priced.

The problem with using a CM3410 as a preamp is that the gain is a bit too low for the "typical" installation. By "typical" I mean 100' of RG6 (5 dB loss at 700 MHz) and a TV with a 6 dB noise figure. I measured my CM3410 to have 15 dB gain and an average UHF noise figure of 2.1 dB (1.5 dB on high VHF).

I like to see the system designed so the system noise figure is not more than 0.5 dB higher than the preamp noise figure. In this case the system noise figure would be 3.0 dB. If the gain was 20 dB then the system noise figure would be just 2.4 dB.

The CM3410, CM7778 and Juice preamps are all a little low on the gain.

The way to take advantage of these low gain preamps and not degrade the system noise figure too much is to add a CM3410 as an in-line amp at the end of the 100' RG6 run. In order to reduce the possibility of overloading the TV, a 10 dB attenuator should added to the CM3410 output. Alternately a CM3412 with 6 dB attenuators can be used on the outputs or use a CM3414 or CM3418 with no output attenuators.

The system noise figure using a CM3410 as the preamp and a CM341x with appropriate attenuators will give you an average system noise figure of 2.4 dB on UHF with the least chance of overload. A further advantage of this design is that you can drive up to 8 TVs with the same system noise figure as one TV.

Last edited by Calaveras; 04-04-2016 at 07:57 AM.
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Old 04-04-2016, 12:34 PM
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From reviewing tens of thousands of posts, 100-ft would be an unusually LONG run....most are in the 40-60 ft range (and only 5-10 ft Mast), so about 3 dB Loss in MOST cases. Which is just what is needed to provide 3x3dB = 9 dB reduction in Intermod Levels (Net SNR improvement of about 6 dB). Mast-mounted Preamp would obviously be better....but only if a SUITABLE Preamp was chosen (e.g. Low Gain CM7778 in High Signal Level Environment) or a High Gain Preamp has higher than "usual" Overload characteristics (e.g. A-D Juice)....or poor Overload Preamp (e.g. CM7777) with the "right" amount of Attenuation inserted on the Input to Maximize the SFDR (Spurious Free Dynamic Range)....there is no such thing as "normal"....nor is there just ONE solution for all applications.....
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Old 04-04-2016, 06:17 PM
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Quote:
Originally Posted by holl_ands View Post
From reviewing tens of thousands of posts, 100-ft would be an unusually LONG run....most are in the 40-60 ft range (and only 5-10 ft Mast), so about 3 dB Loss in MOST cases. Which is just what is needed to provide 3x3dB = 9 dB reduction in Intermod Levels (Net SNR improvement of about 6 dB). Mast-mounted Preamp would obviously be better....but only if a SUITABLE Preamp was chosen (e.g. Low Gain CM7778 in High Signal Level Environment) or a High Gain Preamp has higher than "usual" Overload characteristics (e.g. A-D Juice)....or poor Overload Preamp (e.g. CM7777) with the "right" amount of Attenuation inserted on the Input to Maximize the SFDR (Spurious Free Dynamic Range)....there is no such thing as "normal"....nor is there just ONE solution for all applications.....

I don't understand why you're criticizing. I never said anything about "normal" and I certainly never said that there's only one solution for all applications. I defined what I meant by "typical." The advice I gave above for using two lower gain amps is a good way to maximize SFDR without thinking about it too much.

I have always advocated using a preamp with no more gain than necessary to minimize overload problems.

I am critical of putting an attenuator ahead of a preamp. There are better ways to approach the problem of overload if that's an issue. It makes no sense to me to purposely increase the system noise figure with an attenuator or (depending on how you look at it) reduce the antenna gain.

1) Use a preamp with no more gain than necessary and select a high IP3 model. If that's not good enough to prevent intermod issues....

2) Don't use a preamp but instead use a low noise distribution/in-line amp at the TV such as the CM-341x series. This is a compromise between no preamp and a mast mounted preamp. You won't get all the advantages but it's better than no preamp. If that's still not good enough to prevent intermod issues....

3) Don't use any preamp. It's pretty hard to overload a TV with no amp ahead of it and some coax loss.

There are limits to what can be done. If you live in a very high signal area it may not be possible to receive the weakest stations that might be possible in a weak signal area.

I always keep in mind that most every person who starts on antenna thread is not that technical and just wants to receive their local stations reliably so they can watch TV. There's no point in bombarding them with all sorts of numbers and other technical data. I find it better to do the analysis for them and point them to the hardware they'll need and leave it at that.
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Old 05-23-2016, 07:01 PM
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Quote:
Originally Posted by ota.dt.man View Post
<div class="quote-container"><span>Quote:</span>
<div class="quote-block">Originally Posted by <strong>tylerSC</strong> <a href="/forum/post/21672028"><img alt="View Post" class="inlineimg" src="/img/forum/go_quote.gif" style=""></a><br><br>
Just wondering, if I ever had to replace the old Channel Master power supply ...</div>
</div>
<br>
You won't need to use a different power supply (PS). The CM-0747 is sold separately:
<ul><li><a href="http://www.channelmasterstore.com/CM0747_Replacement_Power_Supply_CM_0747_p/cm-0747.htm" target="_blank">http://www.channelmasterstore.com/CM..._p/cm-0747.htm</a></li>
<li><a href="http://www.starkelectronic.com/allamps.htm" target="_blank">http://www.starkelectronic.com/allamps.htm</a></li>
<li><a href="http://www.summitsource.com/channel-master-0747-replacement-power-supply-spartan-titan-preamplifier-117-volt-ac-factory-replacement-power-supply-75-ohm-output-part-cm0747-p-9164.html" target="_blank">http://www.summitsource.com/channel-...47-p-9164.html</a></li>
<li><a href="http://www.warrenelectronics.com/antennas/0747.htm" target="_blank">http://www.warrenelectronics.com/antennas/0747.htm</a></li>
<li><a href="http://www.wiredathome.com/channel-master-cm-0747-replacement-preamplifier-power-supply/" target="_blank">http://www.wiredathome.com/channel-m...-power-supply/</a></li>
</ul>
The 0747 appears more substantial than the new model PS and has stood the test of time. It's been used for the 7775 / 7777 / 7778, Spartan 3, and Quantum 3 preamps.
The new Channel Master cm-7777HD has a lower noise figure and other added features including a built in LTE filter to null cell transmissions. I currently have been using Blake Aerials LTE filters for cell disruptions here in Fort Wayne. Channel master has an in line LTE filter finally on the market.
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Old 05-24-2016, 11:02 AM
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ProjectSHO89: Installation Instructions for CM7777HD "Amplify" shows that it comes with TWO TIE-WRAPS that the user can pass through the closely spaced "Slots" on either end....perhaps to attach it to the Mast or Yagi Boom:
http://downloads.channelmaster.com/S...tion+Sheet.pdf
And for a much more secure connection, I'm sure I could a PAIR of the fol. very common Mast Clamp types, attaching through one of the holes at each end of the CM7777HD to the Mast:
http://ecx.images-amazon.com/images/I/41AkteAXpmL.jpg
http://www.cooperindustries.com/cont...ar_kit_220.jpg

CM7777HD Amplify Spec Sheet indicates that is has some sort of LTE Filter....but the only spec says "770~1000 MHz Greater Than 20 dB Down" [which be good for the EURO LTE Band which starts at 800 MHz):
http://downloads.channelmaster.com/S...spec+sheet.pdf

SO we have NO IDEA how much Attenuation is provided from 734-758 MHz to suppress the two adjacent Cell Tower TRANSMIT Bands....nor do the specs stipulate how much Loss there may or may not be on 698 MHz, the top of Ch51...which becomes an important issue for LTE Filters that ACTUALLY WORK, which are listed in my post re this same subject:
The Official AVS Antenna and Related Hardware Topic!
Be sure to read down a few posts to find my UPDATE listing additional LTE Filters.

BTW: You should NOT NEED an LTE Filter, unless you have a 4G/LTE Cell Tower within about 2-miles of your location (and even then they may not be transmitting Max Power). See my post after the cited one for a link to some Cell Tower Finder websites. And FYI: LTE will primarily interfere with UPPER UHF (e.g. Ch40-51).....

aerial1: Since they are made in U.K., wouldn't Blake LTE Filter be targeted for EURO LTE Band, which begins at 800 MHz (vice our 700 MHz)?????

Last edited by holl_ands; 05-25-2016 at 01:56 PM.
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Old 05-25-2016, 06:04 AM
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Quote:
ProjectSHO89: Installation Instructions for CM7777HD "Amplify" shows that it comes with TWO TIE-WRAPS that the user can pass through the closely spaced "Slots" on either end....perhaps to attach it to the Mast or Yagi Boom:
http://downloads.channelmaster.com/S...tion+Sheet.pdf
And for a much more secure connection, I'm sure I could a PAIR of the fol. very common Mast Clamp types, attaching through one of the holes at each end of the CM7777HD to the Mast:
http://ecx.images-amazon.com/images/I/41AkteAXpmL.jpg
http://www.cooperindustries.com/cont...ar_kit_220.jpg
The instructions are pretty vague and don't give any details on how to use those straps. One of the reviewers indicated exactly that and also indicated they were metal. Also left undisclosed is the disposition of the USB power input port that's there for indoor usage (eg. line amp application).

I see zero opportunity to use this as a masthead preamp in its out-of-the-box configuration without experiencing water infiltration issues.

All in all, it looks like a half-..... (baked) idea.
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Old 05-25-2016, 02:00 PM
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I don't understand why you're RAINING on CM's Parade.....Installation instructions show it being used the same way as any other OUTDOOR Mast-Mounted Preamp, with DC Power coming up the Coax Downlead. CM wouldn't NEED to mention what to do with the USB Power Input Port if it is weather resistant to begin with...which I would presume it is, since "Weatherproof USB Terminators" aren't readily available (although it would be nice if they would SAY that). The Instructions clearly state the following, from which I would presume the USB Power Port is ALSO Weatherproof [if in doubt, give CM Support a call/email]:

"The heavy-duty weatherproof housing will accommodate installation outdoors as well as indoors."


Last edited by holl_ands; 05-25-2016 at 02:07 PM.
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