Teardown of "Xfiniy" SMC Networks SMCD3GNV 2.4/5Ghz Wireless Cable Modem Router - Page 1
Forum section: electronics / rf-microwave

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 05, 2017, 02:41:50 am
content: This is the cable modem that comcast charges you 10$ a month for. It's a wireless 802.11N 2.4GHz and/or 5GHz wireless router and cable modem. I want to get better range out of this by making a yagi antenna for it or using the existing elements inside of it as the driven elements. But the fact that there are three needs to be sorted out first. I have a few ideas how it works. There are two mounted horizontally on the top and one vertically on the side near the base. The connectors are tiny coax connectors that have two conductors until it goes into a thicker part covered in heat shrink then it looks like just a one conductor wire, very tiny might just be a splice. All antenna elements are identical.1. There is one receive antenna and two transmitter antennas for the two bands. That would increase efficiency of the transmitter?2. Since they are the same size they might use two for the 2.4 and one for the 5? If so:-Would you want the ones on the top to be the 2.4 and the side one to be 5GHz?-Would you want one top and side to be the 2.4 giving you horizontal and vertical polarization, but that would seem detrimental to the 5 GHz?The 5GHz is much faster but as soon as you have a wall or a ceiling in the way the signal goes down, so unless you are in the same room the 5GHz doesn't offer any advantage. So I was going to make the directional antenna on the 2.4Ghz, also because at 5GHz the antenna is so small it becomes hard to build because the size difference is in the elements starts to be well with in the margin of error when cutting small wires.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 05, 2017, 02:47:02 am
content: Close ups of wires and ant elements.Are these folded dipole or J pole antennas? It looks like they went through some effort to solder the wire at that specific point across both sides of the metal leaving a small closed gap. Why?

author: ebclr
author_rank: Super Contributor
timestamp: January 05, 2017, 03:54:42 am
content: Does not reivent the whellhttps://www.amazon.com/Coredy-Extender-External-Antennas-CX-E120/dp/B01M6B0N2C/ref=sr_1_7?ie=UTF8&qid=1483588389&sr=8-7&keywords=wifi+ac+repeater

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 05, 2017, 04:14:12 am
content: Another thing I just noticed one of the top elements and the side elements have the same length wire running to them, which is about twice as long as the the third one. Could these be the 2.4 GHz antennas

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 05, 2017, 04:26:52 am
content: Quote from: ebclr on January 05, 2017, 03:54:42 amBut also costs 52$ plus what ever amazon feel like charging for shipping that day.I also don't like that bullshit graph that compares apples and oranges. It compares wireless g to n, then compares that to their repeater. Wireless G has nothing to do with it. It claims that it increases 800Mbs vs 300 for the N spec device. Any piece of hardware is an extra hurdle. Thats like adding a plug in device to your Ethernet cable and expecting it to go faster.I have watched enough of Daves videos to see through the bull shit. Its just a simple repeater.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: January 06, 2017, 12:42:45 am
content: Here are some specs of the modem I found. It would be interesting to compare this to other modems to see which are faster. As far as the link to the repeater on Amazon it claims 800Mb/s speed but the source it connects to only goes to has "2.4GHz with 300/450 Mbps PHY data rate" at 18 dbm power output, so you couldn't get 800Mb/s if you wanted to.I saw on hack 5 how the FCC limits the "watts" that can come out of these legally. Some wifi devices have more TX power but will use an antenna with less gain or a lower power receiver with a more efficient antenna. Some receivers can be adjusted to put out more watts, then you can just add a more efficient antenna giving you an equivalent of about 60 watts, more if you don't really care about the rules! Those kind of powers could give your wifi the range of a cell phone. I think the easiest way to boost signal would to choose a wifi device with a "detuned" antenna and put on a better one.http://web.archive.org/web/20101207035322/http://www.smc.com/files/AX/SMCD3GNVFeatureSheet.pdfHARDWARE FEATURESPlatform independent – works with PC,OSX,Linux, MAC, UNIXDOCSIS 1.0/1.1/2.0/3.0 compliantF type RF connector for cable networkinterfaceFour RJ-45, 10/100/1000 Ethernet connectorfor LANTwo RJ-11 connector for voiceUSB 2.0 Host PortOne AC 110V power inputSOFTWARE FEATURESCompliant to MCNS DOCSIS 1.1/2.0/3.0specificationsSupports UDP, IP, ARP, ICMP, DHCP, TFTP,SNMP, HTTPSupport G.711(A-Law, Mu-Law), G.723.1, G.729A, G.729E voice compressionVoice Activity Detection(VAD) with ComfortNoise Generation to save bandwidthconsumptionSupport Auto-Jitter buffer adjustment to adaptwith the jitter of Internet trafficKeep alive intervals and backup support toreconnect to redundant serverDHCP, TFTP and ToD clients, provide deviceauto configurationSupport G.168 Echo Cancellation up to 16msSupport caller ID generation for USA, Japanand ChinaNo need to have fixed IPProvide regional profile to accommodate theregulation for different countrySupport standard SNMP, MIB-II, Ethernet-likeMIB, Bridge MIB, RF Interface MIB, CableDevice MIB, Baseline privacy Interface MIBSupports TFTP software downloadPower on self-diagnosticBrowser-based configuration andmanagementEasy to install and friendly to user, just plugand playCOMPLIANT STANDARDDOCSIS 1.0 1.1, 2.0, 3.0PACKET CABLE 1.5WiFi AllianceUPnPUL 60950FCC Part 15 Class BDIMENSIONS (W X L X H)218 x 212x 75 mm8.58.1 x 8.33 x 2.95 inMAX. NUMBER OF CPES64 (64 MAC addresses)FILTERINGLLC: 16, IP: 64RECEIVERDemodulation: 64/256QAMMax Speed: 38Mbps (64QAM)/43Mbps(256QAM) per channelInput Frequency Range: 88Mhz to 1002 MHzDOCSIS 5120 Kbps/10Mbps (QPSK/16QAM)DOCSIS 41.4Mbps (64QAM)/55.2Mbps(256QAM) bonding (DOCSIS) per channelSignal Level-15dBmV to +15dBmV (Automatically GainControlled by CM)17dBmVWIRELESS:16 MB DRAM2T3R 2.4GHz with 300/450 Mbps PHY datarateTX power: 18dBmRX Sensitivity: -76dBm@54Mbps20MHz/40MHz channel bandwidthHardware NAT, QoS, TCP/UDP/IP checksumoverloading. QoS: WMM/WMM-PSSupports L-SIG TXOPEmbedded MIPS 74KC 500MHz with 64KB Icache/32 KB D cacheLegacy and high throughput modesReverse Data Grant (RDG) supportDynamic Frequency Selection (DFS/DFS2)16 Multiple BSSIDSecurity: WEP-64/WEP-128/TKIP/AES/WPA/WPA2/HWWAPIWPS (WiFi protected setup) PBC, PINTRANSMITTERModulation64/256QAMTDMA: QPSK, 8QAM, 16QAM, 32QAM,64QAMS-CDMA: QPSK, 8QAM, 16QAM, 32QAM,64QAM,128QAMMax SpeedOver 120Mbps with 4 bonding upstreamchannelsFrequency Range5 to 42MHz (edge to edge) DOCSISBandwidth0.2, 0.4, 0.8, 1.6, 3.2MHzTDMA: 200, 400, 800, 1600, 3200, 6400 kHzS-CDMA: 1600, 3200 and 6400 kHzSignal Level+8dBmV to +58dBmV (QPSK)+8dBmV to +55dBmV (16QAM)TDMA:+8 to +54 dBmV (32QAM, 64QAM)+8 to +55 dBmV (8QAM, 16QAM)+8 to +58 dBmV (QPSK)S-CDMA:+8 to +53 dBmV (all modulations)(Output level of CM can automaticallycontrolled by CMTS through power rangingfunction), Step: 1dBOutput Return Loss> 6 dB (5-42 MHz) and (91~857 MHz)TELEPHONYSupervisory Voltage: 48V dc nominalMaximum Loop Length: 1500 ft (457M) of 26AWG (0.4 mm) wireRinging Load Capacity: 5 REN per lineProgrammable Interface for Worldwide: Selectby country code and modem config fileProtocolNCS/MGCP 1.0 for PC 1.5SIP RFC3261 for PC 2.0 (in later softwarerelease)CODECG.711A, G.726, G.728, G.729E, T.38, G.722Fax Support & Fax Relay over IP: T.38LEDFront Panel: Power, US/DS, Online, WiFi, Tel 1,Tel 2, BatteryConnector Side: Active Ethernet LAN for 4 portOSSProtocol: ICMP/SNMP V1, V2c, V3MIB: MIB II / MCNS MIB/Hitron ProprietaryMIB, PKT-SP-MIB-EXSIG1.5-I01-050128BATTERY BACKUP WITH LITHIUM BATTERYCELLS2600mAH - 5hrs operation and 8 hrs standbyPOWERInput DC: AC 110VConsumption: TBDENVIRONMENTOperating temperatureRegular Model 32 F (0 C) to 104 F (40 C)Operating humidity10% to 90% (Non condensing)Storage temperature-4 F (-40 C) to 140 F (80 C)Surge ProtectionOn RF Input shall sustain at least 4.5 kVOn Ethernet RJ-45 shall sustain at least 3KV.