Elecraft_K-2_Z-10000_user.pdf

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1、 Assembly and Operations Manual Z10000 Broadband Buffer Amplifier Elecraft K2 Version Z10000-U or “Universal” modelThe same PCB as the Z10000-K2, but without the frequency-dependent parts. The Z10000-U is broadband. The Z10000 is intended to provide a high impedance interface to Clifton Laboratories

2、 Z90 and Z91 SpectraScan Panadapter, but may also be used as a general purpose buffer amplifier. 1.2 Specifications The Z10000-K2 and U models share many specifications: Parameter Common to Z10000-K2 and Z10000-U Physical size Approx 1.4” (35 mm) x 1.25” (32 mm). Height approx 0.2” (5 mm) plus clear

3、ance for wiring. Mounting hole: clearance for 4-40 machine screw. Power Requirements +12V at approx 20 mA. On board regulator permits operation with 30V maximum supply voltage. Connectors None. Direct wire (coaxial cable) connection via solder pads. User may install headers (0.1”) spacing if so desi

4、red. Gain User settable via programming resistor. Different maximum and minimum for K2 and U models. Output Impedance 50 ohms; short circuit protected. Active Devices 78L09 voltage regulator AD8007 amplifier Reverse Isolation Typically 80 dB at 4.915 MHz; depends on cable routing as stray coupling b

5、ecomes important at this level of isolation. Less isolation at higher frequencies. See Section 1.3.3. Harmonic Distortion (2nd and 3rd harmonic) Typically 80 dB below carrier; depends on gain setting and input level 3rd order intermodulation distortion Typically -70 dB below output for signal levels

6、 found in receiver input stages. IP3 depends on gain setting and frequency, typically +30 dBm. Clifton Laboratories Buffer Amplifier Assembly and Operation Page 2? Input Signal L evel DC not to exceed 25 volts; AC input level depends on gain setting; typically used with a less than 100 mV PP input.

7、Parameter Z10000-K2 Z10000-U Bandwidth Flat within 1 dB over 200 KHz range centered on 4915 KHz. Rolled off above 6 MHz and below 4 MHz. Depends on gain. If set for +6 dB net gain, usable bandwidth 100 MHz. (See typical performance plot) Low frequency response extends to below 50 KHz.1 Input Impedan

8、ce Depends on bias isolation resistor setting; used to provide extra roll off and loss; recommended values range from 1 K to 4.7K ohm Depends on frequency and attachment technique. Greater than 1.5 K ohm to 10 MHz, (See typical performance plot) Gain Depends on R905 hence to provide net 0 dB from K2

9、 antenna port to Z10000 output requires the buffer amplifier to operate with signifcant negative gain (loss). Unit 3A prototype Z10000-U ampllifier, set for 6.7 dB nominal net gain. 1.3.1 Frequency Response and Gain 1 It is possible to extend the Z10000s low frequency response to 3 KHz by replacing

10、all 0.22F capacitors with 1.0F. The Z10000-U used in the test data presented has this modification. 2 The theoretical gain for the tested configuration is 9.9 dB, representing 15.9 dB amplifier gain, followed by 6 dB loss resulting from the series 49.9 ohm output series resistance. Clifton Laborator

11、ies Buffer Amplifier Assembly and Operation Page 3? The data presented in this manual was taken with two vector network analyzers; a Hewlett Packard model 8752B and an HP model 87510A. Both VNAs assume the device under test is terminated with the network analyzers impedance, 50 ohms (The 8752B is a

12、75 ohm test set and is used with minimum loss 75:50 ohm matching pads for all measurements presented.) Since the buffer amplifiers impedance significantly exceeds 50 ohms, a false gain will be observed due to the network analyzers output voltage nearly doubling (+6 dB gain) into a high impedance loa

13、d. To prevent this effect from distorting the gain results, all amplifiers under test have their input is terminated with a 49.9 ohm shunt resistor. At 5 MHz, Unit 1s measured gain is 9.78 dB, only 0.12 dB less than theoretically predicted. The 3 dB bandwidth extends from 3 KHz to 174 MHz. Unit 2, p

14、resented below, shows the effect of the K2-specific frequency shaping components. Both above and below the K2 IF frequency (4.9 MHz), the Z10000-K2s gain rolls off. At the desired 4.9 MHz, the net gain is -9.6 dB, necessary to offset the K2s post- mixer ampllifier gain when a net 0 db transfer gain

15、is desired. Clifton Laboratories Buffer Amplifier Assembly and Operation Page 4? 1.3.2 Input Impedance The buffer amplifiers input impedance is dominated by two elements; the bias isolation resistor (4.7 K in the test amplifier) and shunt capacitance (the shunt capacitance of the PCB traces, connect

16、ing wires to the amplifier and the amplifiers input capacitance.) The measured data presented at the right (from Unit 3) should be considered as representative of an amplifier with short (a few inches) coaxial cable input leads. 1.3.3 Reverse Isolation The buffer amplifiers reverse isolation is a fu

17、nction of frequency, as illustrated in the amplifier measurements presented at the right for Unit 1. At 8 MHz, the measured sample exhibited 115 dB reverse isolation. Reverse isolation is also affected by how the amplifier is housed, lead dress, shielding, etc. Accordingly, the isolation illustrated

18、 at the right may not be achieved in every instance. Clifton Laboratories Buffer Amplifier Assembly and Operation Page 5? 1.3.4 Intermodulation Performance The illustration at the right shows the output of Unit 1 with two equal signals (9900 KHz and 10100 KHz) of -10 dBm applied to the amplifier inp

19、ut. The amplifier output is 0 dBm (a 3 dB attenuator is applied ahead of the spectrum analyzer in this plot.) The third order intermodulation product is -71.8 dBm down from either tone. With an output based reference, therefore, the IP3 is thus +35.9 dBm. Clifton Laboratories Buffer Amplifier Assemb

20、ly and Operation Page 6? 2.0 Schematic and Circuit Description 2.1 Universal Version Clifton Laboratories Buffer Amplifier Assembly and Operation Page 7? 2.2 K2 Version 2.3 T heory of Operation The operational circuitry of both buffer amplifiers is similar, with differences in component selection fo

21、r frequency shaping in the K2 version. 2.3.1 Power Supply. The AD8007 amplifier is rated at an absolute maximum operating voltage of 12V. In order to provide a safety margin, and to decouple the amplifier from the power supply, U902, a three-terminal fixed regulator, provides a source of stable +9V

22、to U901. C907 and C908 provide additional decoupling. U901, the AD8007 amplifier, obtains its power via the RC decoupling network comprised of R902, C902 and C906. Since the circuit operates from a single positive power supply, it is necessary to bias U901s input to approximately V/2. This is accomp

23、lished by the 2:1 voltage divider chain of R902/R903. C903 bypasses the V/2 reference voltage; whilst R905 increases U901s input impedance by isolating C903s RF ground. R905s maximum value is determined by the U901s input bias current on the positive pin, specified by Analog Devices as 8A. For 4.7 K

24、, this bias current represents an IR drop of 38 mV. With a DC gain of 4, the corresponding output DC offset will be about 150 mV. If absolutely necessary for high input impedance, R905 may be substituted with a higher value resistor, up to approximately 22 K. However, at frequencies above a few MHz,

25、 the input impedance is Clifton Laboratories Buffer Amplifier Assembly and Operation Page 8? dominated by shunt capacitance; increasing R905 should be done only with an understanding of all the factors affecting the input impedance.3 2.3.2 Amplifier U901, an Analog Devices AD8007, is a high performa

26、nce, low noise c urre nt fe e dbac k amplifier, with a gain-bandwidth product exceeding 650 MHz. A current feedback amplifier is also known as a “transimpedance” amplifier. Analog Devices describes how a current feedback amplifier works: First, the negative input of a CFA responds to current; the ou

27、tput voltage is proportional to that current, hence transimpe danc e (V(out) = Z(t) I(in). Instead of keeping the negative input current small by maintaining high input impedance, and using feed-back and voltage gain to keep the input voltage difference small, the CFA keeps the voltage difference sm

28、all by virtue of its low input impedance (like looking back into a low-offset emitter follower); and it keeps its net input current small dynamically by feedback from the output. When an ideal CFA is driven at the high-impedance positive input, the negative input, with its low impedance, follows clo

29、sely in voltage; and the high gain for error current and the negative feedback through Rf require that the currents through Rf and Rin be equal; hence V(out) = V(in)R(f)/R(in) + 1, just like for voltage-feedback amplifiers. A major difference is that the slew rate can be quite high, because large tr

30、ansient currents can flow in the input stage to handle rapid changes in voltage across the compensating capacitor(s). Also, the low impedance at the negative input means that stray input capacitance will not substantially affect the amplifiers bandwidth. U901s gain (in dB) is determined by the ratio

31、 of resistors R906 and R907: 907 907906 log20 10 R RR Gain + = In the Z10000-K2 version, R905 and C901 form a high-pass RC filter and input attenuator. Adjusting R905 to values below 4.7K will increase the input attenuation, which is desirable to achieve the desired amplifier gain when used in a K2.

32、 The Z1000-K2s output stage also uses RC high pass filtering (R908 depending on your sound card gain it may be necessary to reduce R907 to 100 ohms or even 49.9 ohms for increased net gain.) Note that as the Z10000s gain is increased, the clipping point of the amplifier decreases. Larry, N8LP, repor

33、ts that with R907 at 120 ohms, the clipping point is -5 dBm. Of course, -5 dBm represents an extremely strong signal, unlikely to be encountered in most K2 environments. If you decide to use connection point Option 1, gain setting in the K2 version buffer amplifier is a bit more complex, because the

34、 normal operating mode in a K2 transceiver requires a negative net gainin other words, a net lossof about -14 to -15 dB. Part of the negative gain is obtained by intentional rolloff in C901 and R905.4 This combination provides a net gain of about -14 dB. This much loss is required because the recomm

35、ended K2 connection point has approximately 18 dB net gain from the K2s post-mixer amplifier, Q22 (2N5109). The Z90 is designed for optimum signal level when the net gain between the antenna and the Z90s input is approximately 0 dB.5 When combined with the approximately 3.5 dB loss of the supplied 4

36、.915 MHz bandpass filter, setting the Z10000-K2s gain at -14 dB meets the “net zero gain” requirement. (This computation assumes the K2 is operating in the “normal” mode, i.e ., pre-amp off and attenuation off.) Dont worry, by the way, about achieving this “net zero gain” objective perfectly. A few

37、dB one way or the other is not critical. If you are to err, however, better results will usually be found if you err on the side of operating the Z10000-K2 with a greater loss than operating it for higher gain. Although developed with Clifton Laboratories Z90/91 panadapter, measurements shows that n

38、et 0 dB transfer gain (from K2 antenna input to Z10000 sample output) is an excellent operating point for the Softrock Lite 6.2 receiver when used as a panadapter or second receiver. If desired, of course, the Z10000s gain can be increased as discussed herein. The following three figures show the ne

39、t gain out of the Z10000-K2 as a function of R907 for three values of R905, 4.7K, 2.2K and 1.1K. 4 It would be possible, of course, to dispense with the buffer amplifier completely and connect the Z90 to the K2s IF with a resistive matching pad. However, the resistive matching pad will not provide i

40、solation as does the Z10000-K2. Although the Z90 has relatively low undesired emissions from its input connector, the extra isolation of the buffer amplifier provides additional protection against unwanted signals entering the K2s IF amplifier chain. 5 In other words, a 1 V signal at the frequency t

41、he receiver it tuned to should yield about a 1 V signal at 4915 KHz into the Z90. Clifton Laboratories Buffer Amplifier Assembly and Operation Page 12? Clifton Laboratories Buffer Amplifier Assembly and Operation Page 13? 3.0 Assembly 3.1 Parts L ist The Z10000 parts are packaged in a several small

42、envelopes, depending upon the option purchased. All Z10000 kits: Resistors. All surface mount resistors, for both the U and K2 versions. All R Capacitors for the U version All Cap Printed circuit board PCB Semiconductors (AD8007 and 78L09) Semi K2 Frequency Sensitive Parts Capacitors and inductors n

43、ecessary to shape the amplifiers frequency response to peak at 4.9 MHz. K2 Freq Internal Mounting Parts associated with mounting the Z10000 (either U or K2) inside a receiver. Int K2-specific internal connectors are supplied where the purchaser selects the Internal Mounting option and also the K2 fr

44、equency sensitive parts. K2 Con Clifton Laboratories Buffer Amplifier Assembly and Operation Page 14? If ordering a Z10000-K2, therefore, you will have several extra capacitors and resistors that are not used in the K2 version, as all kits are shipped with the full set of U parts. When working with

45、capacitors particularly, do not removed the individual parts from their color-coded packaging until you are ready to use the component, as their values are not marked on the part and cannot normally be visually distinguished. Hence, if you mix up the capacitors, you will have to measure their values

46、 with a capacitance meter. Also, do not confuse 100 ohm 1% resistors (identified as 1000) with 1.0K ohm 1% parts, identified as 1001. Note that the schematic identifies parts with the multiplier as the “decimal” point. For example a 1K ohm resistor is identified as a 1K0, and a 49.9 ohm resistor as

47、49R9. Common Components - K2 and Universal Models Envelope Typical Photo DesignationValueMarkingNumber Qty C902 0u01 Not markedAll Cap 1 C903 0u1 Not markedAll Cap 1 C904 0u22 Not markedAll Cap 1 C906 1u0 Not markedAll Cap 1 C907 0u1 Not markedAll Cap 1 C908 0u1 Not markedAll Cap 1 R901 200R 2000All

48、 R 1 R902 10R 10R0All R 1 R903 1K0 1001All R 1 R904 1K0 1001All R 1 R906 499R 4990All R 1 R908 49R9 49R9All R 1 U901 AD8007 AD8007ARZSemi 1 U902 LM78L09KA78L09AZSemi 1 ? ? ? Clifton Laboratories Buffer Amplifier Assembly and Operation Page 15? Envelope Typical Photo DesignationValueMarkingNumber Qty

49、 Z10000-K2 Only C901 8p2 Not markedK2 Freq 1 C905 5600pF Not markedK2 Freq 1 C910 1200pF Not markedK2 Freq 1 C911 1200pF Not markedK2 Freq 1 C912 1200pF Not markedK2 Freq 1 L901 1u5 K2 Freq 1 L902 1u5 K2 Freq 1 Z10000-U Only C901 0u1 Not markedAll Cap 1 C905 0u22 Not markedAll Cap 1 L901 0 ohm jumper All