FCCID.CO- FCC ID Database
HomeCompaniesEquipment ClassesSearch

© 2026 FCC ID Database. All rights reserved.

AboutContactData sourced from FCC public records
  1. Home/
  2. Shenzhen Hongtai Electronic Hardware Co., Ltd/
  3. 2BPZM-T7FM

2BPZM-T7FMAir Key

Shenzhen Hongtai Electronic Hardware Co., Ltd
Air Key - FCC ID 2BPZM-T7FM - Shenzhen Hongtai Electronic Hardware Co., Ltd
Click to zoom

Application Details

Equipment Class
DTS - Digital Transmission System
Date of Grant
Nov 28, 2025
Application Purpose
Original Equipment
Equipment Note
Air Key
Frequency Range
2402.00000000 - 2480.00000000
Company
Shenzhen Hongtai Electronic Hardware Co., Ltd
Country
China

Documents & Files

Select a file to view

Users Manual

↗

Attestation Statements

↗
↗

Cover Letter(s)

↗
↗

External Photos

↗

ID Label/Location Info

↗

Internal Photos

↗

RF Exposure Info

↗

Test Report

↗
↗
↗

Test Setup Photos

↗

Document Text

Text extracted from the exhibit documents filed with the FCC. Open a document above to read the original.

Users Manual

               ! "            "                  "#       "$                      %!  " %$    " %      &'(( )&*)+, -.'(/01**2)+)31)4'43()56)47)(&)+43+7'89:*)&2(7&73(;'42)16, .30*7'(<=(>&23(?)/'4@'+7A&3*7'(/*'*27/+)B7&)('*)5617&7*1>3664'B)+C>@3(0;3&*04)4     "      ! "D E     FG    FHG         "    I     "      J   "

Attestation Statements

Shenzhen Hongtai Electronic Hardware Co., Ltd 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Federal Communications Commission Authorization and Evaluation Division Equipment Authorization Branch 7435 Oakland Mills Road Columbia, MD 21046 2025/11/26 U.S. Agent Designation Shenzhen Hongtai Electronic Hardware Co., Ltd acknowledges their consent for the following contact located in the United States to act as their agent for service of process for the equipment for which authorization is sought (FCC ID: 2BPZM-T7FM): Name and company of U.S. agent: GLOCERTS TECHNOLOGY INC Physical U.S. address of agent: 19784 SUNKISSED RIDGE DR RIVERSIDE, CA 92507 United States FRN of U.S. agent: 0036339737 Email address of U.S. agent: [email protected] GLOCERTS TECHNOLOGY INC acknowledges their obligation to accept service of process on behalf of Shenzhen Hongtai Electronic Hardware Co., Ltd Shenzhen Hongtai Electronic Hardware Co., Ltd with the FRN [0037128121] accepts its obligation to maintain an agent for service of process in the United States for no less than one year after either the grantee has permanently terminated all marketing and importation of the applicable equipment within the U.S., or the conclusion of any Commission-related administrative or judicial proceeding involving the equipment, whichever is later. By signing this form, we confirm the above and that we are aware of the application requirements listed under § 2.911(d)(7). The information provided in this letter is based on the referenced rule parts of Title 47 of the CFR as well as KDB 986446 D01. An expiration date for this letter does not exist. In case the U.S. agent changes, the grantee is obligated to notify the FCC within 30 days via the granting TCB. Sincerely, Signature Rongtian Ma Manager Shenzhen Hongtai Electronic Hardware Co., Ltd Signature Huiying Fan Director GLOCERTS TECHNOLOGY INC 48_[mo del] US_Agent_2.911(d)(7) - U, V0 5

External Photos

FCC ID: 2BPZM-T7FM External Photos of the EUT FCC ID: 2BPZM-T7FM

ID Label/Location Info

Label and Location Size: L: 2.0cm*W: 1.0cm Label and Location FCC ID : 2BPZM-T7FM

Internal Photos

FCC ID: 2BPZM-T7FM Internal Photos of the EUT FCC ID: 2BPZM-T7FM ANT

RF Exposure Info

Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn RF Exposure evaluation Report Reference No. .................... : FCC ID. ........................................... : CTA25103100402 2BPZM-T7FM Compiled by ( position+printed name+signature) . : File administrators Zoey Cao Supervised by ( position+printed name+signature) . : Project Engineer Ace Chai Approved by ( position+printed name+signature) . : RF Manager Eric Wang Date of issue .................................... : Nov. 07, 2025 Testing Laboratory Name.............. : Shenzhen CTA Testing Technology Co., Ltd. Address ........................................... : Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Applicant’s name ........................... : Shenzhen Hongtai Electronic Hardware Co., Ltd Address ........................................... : 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Standard........................................... : 47CFR §1.1310 47CFR §2.1093 KDB447498 D01 General RF Exposure Guidance v06 Shenzhen CTA Testing Technology Co., Ltd. All rights reserved. This publication may be reproduced in whole or in part for non-commercial purpses as long as the Shenzhen CTA Testing Technology Co., Ltd. is acknowledged as copyright owner and source of the material. Shenzhen CTA Testing Technology Co., Ltd. takes no responsibility for and will not assume liability for damages resulting from the reader's interpretation of the reproduced material due to its placement and context. Test item description ..................... : Air key Trade Mark ........................................ N/A Manufacturer .................................... : Shenzhen Hongtai Electronic Hardware Co., Ltd Model/Type reference ...................... : T7FM Listed Models ................................... : T7FM-1, T7FM-2, T7FM-3, T7FM-4, T7FM-5, T7FM-6 Rating ............................................... : DC 3.0V From battery Result ............................................... : PASS Report No.: CTA25103100402 Page 2 of 8 Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn T E S T R E P O R T Equipment under Test : Air key Model /Type : T7FM Listed Models : T7FM-1, T7FM-2, T7FM-3, T7FM-4, T7FM-5, T7FM-6 Model difference : The PCB board, circuit, structure and internal of these models are the same, Only model number and colour is different for these model. Applicant : Shenzhen Hongtai Electronic Hardware Co., Ltd Address : 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Manufacturer : Shenzhen Hongtai Electronic Hardware Co., Ltd Address : 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Test Result: PASS The test report merely corresponds to the test sample. It is not permitted to copy extracts of these test result without the written permission of the test laboratory. Report No.: CTA25103100402 Page 3 of 8 Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn Contents 1 TEST STANDARDS ............................................................................................................ 4 2 SUMMARY .......................................................................................................................... 5 2.1 General Remarks ..................................................................................................... 5 2.2 Product Description ................................................................................................. 5 2.3 Special Accessories ................................................................................................. 5 2.4 Modifications ............................................................................................................ 5 3 TEST ENVIRONMENT ....................................................................................................... 6 3.1 Address of the test laboratory .................................................................................. 6 3.2 Test Facility .............................................................................................................. 6 3.3 Statement of the measurement uncertainty ............................................................. 6 4 Test limit .............................................................................................................................. 7 4.1 Requirement ............................................................................................................ 7 4.2 Conducted Power Results ....................................................................................... 7 4.3 Manufacturing tolerance .......................................................................................... 7 4.4 Evaluation Result ..................................................................................................... 8 4.5 Simultaneous Transmission for SAR Exclusion ...................................................... 8 5 Conclusion ........................................................................................................................... 8 Report No.: CTA25103100402 Page 4 of 8 Shenzhen CTA Testing Technology Co., Ltd.…

Text truncated - open the document above for the full version.

Test Report

2.4GHz2012ChipAntenna:RANT2012F245C07 Dimension(mm) L2.05+-0.10 W1.20+-0.10 T0.65+-0.10 No.TerminalName 1Feeding/GNG 2GND Application: WLAN,802.11b/g,Bluetooth,WLAN,etc... Features SMD,highreliability,ultraImpact,Omni-directional... PartnumberInformation RANT2012F245C07 (A)(B)(C)(D)(E)(F) (A)ProductTypeChipAntenna (B)SizeCode2.0x1.2mm(+-0.2mm) (C)MaterialHighKmaterial (D)Frequency2.4~2.5GHz (E)FeedingmodePIFA&SingleFeeding (F)AntennatypeType=07 ElectricalSpecification WorkingFrequencyRange2400~2484MHz Bandwidth84(Min.) PeakGain1.7dBi(Typ.) Impedance50Ohm Returnloss10dB(Min) PolarizationLinear AzimuthBeamwidthOmni-directional OperationTemperature( °C )-40~85 °C ResistancetoSolderingHeats 10sec.(@280°C) TerminationNi/Au(Leadless) ThespecificationisdefinedonEVB. DimensionandTerminalConfiguration 咏成 國 際 科 技 有限 公 司 電 話 : 1 35305 7 6606 RAINIn t e rn a t i o n a lT ec hn o l o g y C o . , L t d . Add:Room 707, Building F, Tongan Zhichuangyuan, xixiang street, Baoan District, Shenzhen. 2.4GHz2012ChipAntenna:RANT2012F245C07 EvaluationBoardReference PCBDimensionAntennaLayoutReferenceUnit:mm ElectricalCharacteristics ReturnLoss ReturnLoss&Radiation 1 Frequency(MHz) S11(dB) 2400-10.77 2450-24.81 2484-10.243 Radiation Z Y X 2400MHz2450MHz2500MHz Efficiency70.56%75.25%71.01% 2.4GHz2012ChipAntenna:RANT2012F245C07 TapingSpecifications ReelandTapingSpecification ReelSpecification TYPESIZEABCD 20127”5K/Reel 9.0±0.5 60±213.5±0.5178±2 TappingSpecification PackagingTypeABWEFGHTDP PaperType2012 1.50±0.202.30±0.208.0±0.201.75±0.103.5±0.054.0±0.102.0±0.050.75±0.101.57±0.104.0±0.1 2.4GHz2012ChipAntenna:RANT2012F245C07 ReliabilityTable TestItemProcedure Requirements CeramicType Remark (Reference) Electrical Characterization Fulfilltheelectrical specification UserSpec. Thermal Shock 1.Preconditioning: 50±10°C/1hr,thenkeepfor24±1hrsatroomtemp. 2.Initialmeasure:Spec:referInitialspec. 3.Rapidchangeoftemperaturetest: -30°Cto+85°C;100cycles; 15minutesatLowercategorytemperature; 15minutesatUppercategorytemperature. NoVisibleDamage. Fulfilltheelectrical specification. MIL-STD-202 107 Temperature Cycling 1.Initialmeasure:Spec:referInitialspec. 2.100Cycles(-30°Cto+85°C),SoakMode=1(2Cycle/hours). 3.Measurementat24±2Hoursaftertestcondition. NoVisibleDamage. Fulfilltheelectrical specification. JESD22 JA104 HighTemperature Exposure 1.Initialmeasure:Spec:referInitialspec. 2.Unpowered;500hours@T=+85°C. 3.Measurementat24±2hoursaftertest. NoVisibleDamage. Fulfilltheelectrical specification. MIL-STD-202 108 LowTemperature Storage 1.Initialmeasure:Spec:referInitialspec. 2.Unpowered:500hours@T=-30°C. 3.Measurementat24±2hoursaftertest. NoVisibleDamage. Fulfilltheelectrical specification. MIL-STD-202 108 Solderability (SMDBottomSide) Dippingmethod: a.Temperature:235±5°C b.Dippingtime:3±0.5s Thesoldershouldcover over95%ofthecritical areaofbottomside. IEC60384-21/22 4.10 SolderingHeat Resistance (RSH) Preheatingtemperature:150±10°C. Preheatingtime:1~2min. Soldertemperature:260±5°C. Dippingtime:5±0.5s NoVisibleDamage.IEC60384-21/22 4.10 Vibration5g'sfor20min.,12cycleseachof3orientations Note:Use8"X5"PCB.031"thick7securepointson,onelong sideand2securepointsatcornersofoppositesides.Parts mountedwithin2"fromanysecurepoint.Testfrom10-2000 Hz. NoVisibleDamage.MIL-STD-202 Method204 Mechanical Shock Threeshocksineachdirectionshallbeappliedalongthethree mutuallyperpendicularaxesofthetestspecimen(18shocks) Peakvalue:1,500g’s Duration:0.5ms Velocitychange:15.4ft/s Waveform:Half-sine NoVisibleDamage.MIL-STD-202 Method213 Humidity Bias 1.Humidity:85%R.H.,Temperature:85±2°C. 2.Time:500±24hours. 3.Measurementat24±2hrsaftertestcondition. NoVisibleDamage. Fulfilltheelectrical specification. MIL-STD-202 Method106 2.4GHz2012ChipAntenna:RANT2012F245C07 2.4GHz2012ChipAntenna:RANT2012F245C07 _ Board Flex (SMD) 1.Mountingmethod: IR-Reflow.PCBSize(L:100×W:40×T:1.6mm) 2.Applytheloadindirectionofthearrowuntilbendingreaches 2mm. NoVisibleDamage.AEC-Q200 005 AdhesionForceof1.8Kgfor60seconds.NoVisibleDamage Magnificationof20Xor greatermaybeemployed forinspectionofthe mechanicalintegrityofthe devicebodyterminalsand body/terminaljunction. AEC-Q200 006 Physical Dimension Anyapplicablemethodusingx10magnification,micrometers, calipers,gauges,contourprojectors,orothermeasuring equipment,capableofdeterminingtheactualspecimen dimensions. Inaccordancewith specification. JESD22 JB100 RevisionHistory RevisionDateContent 12020/10/15NewDatasheet

Test Report

Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn FCC PART 15 SUBPART C TEST REPORT FCC PART 15.247 Report Reference No. ...................: FCC ID. ......................................... : CTA25103100401 2BPZM-T7FM Compiled by ( position+printed name+signature) : File administrators Zoey Cao Supervised by ( position+printed name+signature) : Project Engineer Ace Chai Approved by ( position+printed name+signature) : RF Manager Eric Wang Date of issue ...................................: Nov. 07, 2025 Testing Laboratory Name .............: Shenzhen CTA Testing Technology Co., Ltd. Address ..........................................: Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Applicant’s name...........................: Shenzhen Hongtai Electronic Hardware Co., Ltd Address ...........................................: 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Test specification ......................... : Standard ..........................................: FCC Part 15.247 Shenzhen CTA Testing Technology Co., Ltd. All rights reserved. This publication may be reproduced in whole or in part for non-commercial purposes as long as the Shenzhen CTA Testing Technology Co., Ltd. is acknowledged as copyright owner and source of the material. Shenzhen CTA Testing Technology Co., Ltd. takes no responsibility for and will not assume liability for damages resulting from the reader's interpretation of the reproduced material due to its placement and context. Equipment description ................ : Air key Trade Mark ......................................: N/A Manufacturer ...................................: Shenzhen Hongtai Electronic Hardware Co., Ltd Model/Type reference .....................: T7FM Listed Models ..................................: T7FM-1, T7FM-2, T7FM-3, T7FM-4, T7FM-5, T7FM-6 Modulation ......................................: GFSK Frequency ........................................ From 2402MHz to 2480MHz Ratings ............................................: DC 3.0V From battery Result ..............................................: PASS Report No.: CTA25103100401 Page 2 of 28 Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn T E S T R E P O R T Equipment under Test : Air key Model /Type : T7FM Listed Models : T7FM-1, T7FM-2, T7FM-3, T7FM-4, T7FM-5, T7FM-6 Model difference : The PCB board, circuit, structure and internal of these models are the same, Only model number and colour is different for these model. Applicant : Shenzhen Hongtai Electronic Hardware Co., Ltd Address : 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Manufacturer : Shenzhen Hongtai Electronic Hardware Co., Ltd Address : 2nd Floor, Building A, Sha Si Third Industrial Zone, Shajing Street, Bao'an District, Shenzhen China Test Result: PASS The test report merely corresponds to the test sample. It is not permitted to copy extracts of these test result without the written permission of the test laboratory. Report No.: CTA25103100401 Page 3 of 28 Shenzhen CTA Testing Technology Co., Ltd. Room 106, Building 1, Yibaolai Industrial Park, Qiaotou Community, Fuhai Street, Bao’an District, Shenzhen, China Tel:+86-755 2322 5875 E-mail:[email protected] Web:http://www.cta-test.cn Contents 1 TEST STANDARDS ...................................................................................................................................... 4 2 SUMMARY .................................................................................................................................................... 5 2.1 General Remarks .............................................................................................................................. 5 2.2 Product Description* .......................................................................................................................... 5 2.3 Equipment Under Test ....................................................................................................................... 5 2.4 Short description of the Equipment under Test (EUT) ...................................................................... 5 2.5 EUT configuration .............................................................................................................................. 5 2.6 EUT operation mode ......................................................................................................................... 5 2.7 Block Diagram of Test Setup ............................................................................................................. 6 2.8 Related Submittal(s) / Grant (s) ......................................................................................................... 6 2.9 Modifications ...................................................................................................................................... 6 3 TEST ENVIRONMENT ................................................................................................................................. 7 3.1 Address of the test laboratory ........................................................................................................... 7 3.2 Test Facility........................................................................................................................................ 7 3.3 Enviro…

Text truncated - open the document above for the full version.

Test Report

1 FCC Appendix RF Test Data for BLE FCC ID : 2BPZM-T7FM Company : Shenzhen Hongtai Electronic Hardware Co., Ltd EUT : Air key Model Number : T7FM Report No. : CTA25103100401 Reviewed By : Eric Wang 2 Appendix A: DTS Bandwidth Test Result TestMode Antenna Freq(MHz) DTS BW [MHz] FL[MHz] FH[MHz] Limit[MHz] Verdict BLE_1M Ant1 2402 0.644 2401.696 2402.340 0.5 PASS 2440 0.648 2439.692 2440.340 0.5 PASS 2480 0.620 2479.692 2480.312 0.5 PASS 3 Test Graphs BLE_1M_Ant1_2402 BLE_1M_Ant1_2440 BLE_1M_Ant1_2480 4 5 Appendix B: Occupied Channel Bandwidth Test Result TestMode Antenna Freq(MHz) OCB [MHz] FL[MHz] FH[MHz] Limit[MHz] Verdict BLE_1M Ant1 2402 1.0048 2401.5172 2402.5220 --- --- 2440 1.0061 2439.5171 2440.5232 --- --- 2480 1.0011 2479.5180 2480.5191 --- --- 6 Test Graphs BLE_1M_Ant1_2402 BLE_1M_Ant1_2440 BLE_1M_Ant1_2480 7 8 Appendix C: Maximum conducted output power Test Result Peak TestMode Antenna Freq(MHz) Conducted Peak Powert[dBm] Conducted Limit[dBm] Verdict BLE_1M Ant1 2402 -0.01 ≤30 PASS 2440 -0.21 ≤30 PASS 2480 -0.15 ≤30 PASS 9 Appendix D: Maximum power spectral density Test Result TestMode Antenna Freq(MHz) Result[dBm/3kHz] Limit[dBm/3kHz] Verdict BLE_1M Ant1 2402 -15.51 ≤8.00 PASS 2440 -15.59 ≤8.00 PASS 2480 -16.31 ≤8.00 PASS 10 Test Graphs BLE_1M_Ant1_2402 BLE_1M_Ant1_2440 BLE_1M_Ant1_2480 11 12 Appendix E: Band edge measurements Test Result TestMod e Antenn a ChNam e Freq(MHz ) RefLevel[dBm ] Result[dBm ] Limit[dBm ] Verdic t BLE_1M Ant1 Low 2402 -0.39 -54.52 ≤-20.39 PASS High 2480 -0.14 -51.48 ≤-20.14 PASS 13 Test Graphs BLE_1M_Ant1_Low_2402 BLE_1M_Ant1_High_2480 14 Appendix F: Conducted Spurious Emission Test Result TestMode Antenna Freq(MHz) FreqRange [MHz] RefLevel [dBm] Result[dBm] Limit[dBm] Verdict BLE_1M Ant1 2402 Reference -0.55 -0.55 --- PASS 30~1000 -0.55 -53.7 ≤-20.55 PASS 1000~26500 -0.55 -41.99 ≤-20.55 PASS 2440 Reference -1.80 -1.80 --- PASS 30~1000 -1.80 -48.46 ≤-21.8 PASS 1000~26500 -1.80 -43.99 ≤-21.8 PASS 2480 Reference -2.02 -2.02 --- PASS 30~1000 -2.02 -45.94 ≤-22.02 PASS 1000~26500 -2.02 -41.1 ≤-22.02 PASS 15 Test Graphs BLE_1M_Ant1_2402_0~Reference BLE_1M_Ant1_2402_30~1000 BLE_1M_Ant1_2402_1000~26500 16 BLE_1M_Ant1_2440_0~Reference BLE_1M_Ant1_2440_30~1000 17 BLE_1M_Ant1_2440_1000~26500 BLE_1M_Ant1_2480_0~Reference BLE_1M_Ant1_2480_30~1000 18 BLE_1M_Ant1_2480_1000~26500 19 Appendix G: Duty Cycle Test Result TestMode Antenna Freq(MHz) ON Time [ms] Period [ms] X DC [%] xFactor Limit Verdict BLE_1M Ant1 2402 0.41 0.62 0.6613 66.13 1.80 --- --- 2440 0.41 0.62 0.6613 66.13 1.80 --- --- 2480 0.41 0.62 0.6613 66.13 1.80 --- --- 20 Test Graphs BLE_1M_Ant1_2402 BLE_1M_Ant1_2440 BLE_1M_Ant1_2480 21

Test Setup Photos

FCC ID: 2BPZM-T7FM Test Setup Photos of the EUT

Contact Information

Applicant

Rongtian Ma
[email protected]Fax: 18589044591

Test Firm

SHENZHEN CTA TESTING TECHNOLOGY CO., LTD.Eric Wang
[email protected]

Technical Specifications

#Rule PartsFrequency RangePower Output
115C2.40 GHz - 2.48 GHz1.00 mW
Confidentiality
Long Term
Grant Notes
Output Power listed is peak conducted.

Other Applications from Shenzhen Hongtai Electronic Hardware Co., Ltd

2BPZM-T5FM-1

Smart key

Jul 27, 2026

Equipment Class

DTS - Digital Transmission System
Air Key - FCC ID 2BPZM-T5FM - Shenzhen Hongtai Electronic Hardware Co., Ltd
2BPZM-T5FM

Air Key

Nov 28, 2025

Equipment Class

DTS - Digital Transmission System