CB2. 00 4 Zone Conventional Fire Alarm Panel. Thank you all for your support on this project. Please convey my appreciation to all involved. All fitted and working now!! I look forward to working with you guys again in the new year! We attended a week ago and all went smoothly, no problems since (touch wood!). That was very quick and efficient! Just discovered your website today but it looks excellent! Cobra 2. 9 GTL History. History: The Cobra 2. LTD is a later version of the Cobra 2. GTL. Although, the exterior is slightly different, the interior has not changed much over the years. The Cobra 2. 9 GTL, manufactured in Hong Kong and Taiwan, was introduced in the USA in 1. FCC expanded the CB band from 2. The Cobra 2. 9 LTD replaced the Cobra 2. Cobra Electronics supplies product manuals to help support your questions related to your. Misplaced your Cobra product manual? CB Radios; Detection Systems. Owner's manual; Cobra 200GTL DX Owner's Manual. Cobra owner's manual cb radio 19 dx iv. Owner’s Manual AMATEUR 10 METER MOBILE RADIO 200 GTL DX Printed in. CB200e Extinguishing Control Panel User Instructions. Manual Mode If a fire. The Cobra 150 GTL is a AM/FM 10 METER AMATEUR RADIO released by Cobra along with it's sister the 200 GTL (100. GTL shortly afterward. The changes made to the Cobra GTL and designated The Cobra 2. LTD where as follows. The Red LED display was changed to Green. The coil L- 1. 6 was changed from a variable to a fixed component. The instant channel 9 switch was added to the Cobra 2. LTD. The interior was not changed very much. In fact, the service manual published by Sams Photo Facts can still be used for the Cobra 2. LTD. At some point the model name was changed from the Cobra 2. LTD to The Cobra 2. LTD Classic. The service manual for Sams Photo Facts is CB- 2. The Cobra 2. 9 LTD and GTL was manufactured by Uniden for Dynascan. The Uniden 7. 6 and the later version the Uniden 7. Cobra 2. 9 LTD and GTL. The Cobra 2. 9 LTD was first manufactured in Taiwan, and then in The Philippines up until 1. It has been manufactured in China since then. The original design remained the same for a couple of years, and then was overhauled by reducing the size of the resistors, cost, and quality of the components where ever possible. The newest version of the Cobra 2. Cobra 200GTL DX Documentation Project CBTricks.com Frequency Conversion. For a printable mod sheet go here. NOTE: Exercise a great deal of care with this mod! CB200 4 Zone Conventional Fire Alarm Panel. CB200 - Installation Manual; CB200 - Data Sheet; Related Products. Yuasa 12V 2.1AH Battery. LTD has been changed to a greater degree. The following changes have been performed both to the exterior and to the interior in varying degrees. The Cobra 2. 9 LTD chassis now is available with Blue LEDs displays. The analog faceplate is being phased out and a digital display is being introduced. The original 1. 0 pin audio chip TA- 7. YD- 1. 02. 2 and finally the 5 pin TDA- 2. This was done to reduce cost. This PLL uses a single crystal to produce the entire mixer frequencies needed to operate. This is just the start of the operation of the PLL to prevent channel modification. The reference crystal (1. COBRA MT200 MANUAL instructions guide. Manual cobra 200gtl dx service repair manual 705. MHz) is used to time the PLL and is used as a mixer frequency for the receiver. In addition the reference frequency is divided by two to produce a frequency of 5. MHz. This frequency is then multiplied by three to produce a frequency of 1. MHz. Two phase lock loop chips may be found in the Cobra 2. LTD, the u. PC2. 81. PC2. 81. 4. The factory PLL is u. PC2. 81. 6, but some radios may have the 2. PLLs work interchangeably. The u. PC2. 82. 4 lacks the pin allowing the offset function of 4. KHz, and can be found in sideband radios, such as, the Uniden PC- 1. Changes: The first early change in the Cobra 2. LTD was replacing varactor diodes D- 1. D- 1. 6 from board to surface mounted components. These varactors can be found near IC- 2 the VCO mixer. The varactor D- 1. S2. 68. 7D) is used to control the Delta Tune; D- 1. S2. 68. 8EA) is used in the mixer tank circuit L- 1. Modifications: The most common modification found in the Cobra 2. LTD is the disabling of the Transmit audio limiter D- 1. This modification is unauthorized and is not endorsed by the author, The CB Doctor. Disabling the audio limiter may cause the carrier envelope to over modulate. Keep in mind that you can not get more than 1. A power Microphone will make the radio sound louder without exceeding the FCC part 9. It is a fallacy to believe that the radio will transmit further with the audio limiter removed. The radio will show more peak power, but this peak power reading is false. The flatten top and bottom of the carrier envelope will show up as more power because of the duration of the peak reading. Adjusting L- 1. 4 will provide a higher carrier level; depending on the year and place of manufacturing; it will determine the gain of the carrier from the legal 4 watts to 5 to 8 watts. The carrier is needed for a receiving station to lock onto the center (Fundamental) frequency, but is a waste of power and provides no audio information. Some of the modifications that should be avoided are cutting R- 5. D- 8. R- 5. 5 is needed to help provide 5. D- 8 is used to protect the Final and Driver from current flowing backward when the radio is un- keyed. If you see these modifications please restore them to factory. Another modification is replacing the factory 2. SC- 2. 07. 8 with a 2. SC- 1. 96. 9. The 2. SC- 1. 96. 9 can dissipate more heat, but has less gain than the 2. SC- 2. 07. 8. The best combination for more power is using the parts found in the Cobra 2. GTL. The driver 2. SC- 2. 02. 8B and the final 2. SC- 2. 02. 9 will provide more power. The Toshiba 2. SC- 1. I suggest saving any 2. SC- 1. 96. 9 Finals for the purpose they were intended; the 2. SC- 1. 96. 9 is for sideband radios. Specific Details: There are two mistakes on the Sams Photo Facts service manual. The first is the misnaming of the switching transistor. It is marked as TR- 2. TR- 2. 1. It is found near the Final. The second mistake is the voltage marked at the Final is labeled - 1. The PLL Circuit: As I wrote earlier the Phase Lock Loop was required, under the FCC guidelines, to restrict the ease of expanding the Cobra 2. LTD for additional channels. The u. PC- 2. 81. ROM (Read Only Memory). If the binary count is anything other than what is allowed the radio will go into shutdown. Another feature is the use of BCD (Binary Counter Decade). This entails using two sets of binary counters that can only add up to the number 1. This helps limit the number of possible binary combinations to the PLL. The other method to limit channel expansion is the feature on the u. PC- 2. 81. 6 that shifts the radio by 4. KHz between transmitting and receiving. If you are thinking of replacing the 1. MHz reference crystal don’t bother. The frequency between the transmitting and receiver mixers will only increase and the two mixing frequencies will exceed 4. KHz; the result will be that you will not be on the same channel when you transmit and receive. A method that will allow channel expansion is known as “forced signal injection.” The kit to allow for channel expansion can still be found on the market, but is slowly being phased out due to the lack of demand. The illegal export market has killed the legal domestic radio market. I know of only one distributor that still provides a version of the original Expo- Kit. This kit allows 4. CB band. The method used is forcing the loop mixer to “See” a mixing frequency other than the one provided by the Phase Lock Loop chip. This frequency is then mixed with the reference crystal 1. MHz; the difference is 4. KHz. This second I. F of 4. 55 KHz is then rectified and filtered to provide just the audio from a carrier envelope. The Transmitter: The transmitter is a high level modulation circuit. The audio is impressed onto the carrier at the Final and the Driver. For every two watts of carrier one watt of audio is used to produce 1. This non- linear combination of 2. MHz carrier and audio at the Final and the Driver is called a carrier envelope. The Audio Circuit: The audio chip used in the original Cobra 2. LTD is the TA- 7. AP. There have been three versions of the audio chip used over the years. The TA- 7. 22. 22 is the most common and the original audio chip found in the Cobra 2. GTL. The second version was the short- lived YD- 1. The pin out is different than the TA- 7. The third audio chip used today in the Cobra 2. LTD chassis and many of the new export radios is the TDA- 2. This audio chip has been around for 3. It is used as a stand alone audio chip in the newer CB radios. The only reason the chips have been changed is to keep the cost of manufacturing low. Whichever audio chip is used the theory is the same. In the transmit mode the first winding is a center tap to a 1. This supplies the Final and Driver with 1. As the audio chip is fed to the first winding the audio is imprinted on the carrier creating a carrier envelope. In the receive mode the audio is transferred to the second winding, which goes to the speaker. The DC component is isolated using a coupling capacitor. The audio transformer is used in both the receiver and transmitter modes. It is rare, but I have come across audio transformers that have been overheated by a shorted final, and lost their inductive properties because the windings were overheated and melted the protective insulation. It is possible to have some receiver audio but no audio modulation when this happens. Return to Cobra 2. GTL Photos. Return to Cobra 2. LTD early version Photos. Return to Cobra 2. LTD Taiwan early version Golden limited Edition info. Return to Audio Chips. Return to Home Page Return to Radio List.
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