N2CX Accuprobe Plus Assembly Instructions

Transcription

1 N2CX Accuprbe Plus Assembly Instructins First ff, check t see if the parts match the parts list. Electrical cmpnents: R1 1K, 1/4W, 5%, (BRN, BLK, RED, GLD) R2 1M, 1/4W, 5%, (BRN, BLK, GRN, GLD) R3 15K, 1/4W, 5%, (BRN, GRN, ORN, GLD) R4 150K, 1/4W, 5%, (BRN, GRN, YEL, GLD) R5 649K, 1/4W, 1%, (BLU, YEL, WHT,ORN, BRN) R6 20.5K, 1/4W, 1%, (RED, BLK, GRN, RED, BRN) R7 49.9K, 1/4W, 1%, (YEL, WHT, WHT, RED, BRN) R8 6.8K, 1/4W, 5%, (BLU, GRY, RED, GLD) C1, 2.01uF marked (103) C3.1uF marked (104) U1 LMC6482AIN, Op Amp, 8 PIN DIP D1, 2 1N5711 dide D3 Red LED S1,2 DPDT Slide Switch PCB Printed circuit bard Mechanical cmpnents: N size battery hlder Size 23A alkaline battery 4-40 brass nut 4-40 steel nut 2 ea. #4 internal tth lck washers 2 ea x 1/4 L. pan head screws 2 ea ga., #4 ring terminals 3/32 dia. x 2 brass rd 3/16 x 2 L. black heat shrink tubing 3/4 dia. x 5 L. clear heat shrink tubing Small Tyrap 2 RG-174 cax Red banana plug Black banana plug Alligatr clip and lead Read all the instructin befre assembling the N2CX Accuprbe Plus n2cx_accuprbe_plus_assembly_ pdf Page 1 f 12

2 The first item t assemble will be sldering the 4-40 brass nut t the GND. pad n the pcb. Slder the nut, flush t the side f the bard. Use smething square t psitin the bard up against, I used a small piece f wd, and lie the nut dwn 90 degrees t the bard. This will be the alligatr lead cnnectin pint used later. D nt get any slder inside the threads f the nut. All cmpnents are sldered n the silk screened side f the bard. Slder all the resistrs in place, fllwing the abve guide and the silk screened lcatins. Bend the leads 90 and lay the resistrs dwn flat, there are n vertically munted resistrs. Trim all leads after sldering. If yu have any dubt as t the crrect value, duble check them with yur VOM. R5, 6, 7 are 1% resistrs, s they have 5 clr bands. Install and slder all the resistrs: R1, 8-1K, 5%, (BRN, BLK, RED, GLD) R2-1M, 5%, (BRN, BLK, GRN, GLD) R3-15K, 5%, (BRN, GRN, ORN, GLD) R4-150K, 5%, (BRN, GRN, YEL, GLD) R5-649K, 1%, (BLU, YEL, WHT,ORN, BRN) R6-20.5K, 1%, (RED, BLK, GRN, RED, BRN) R7-49.9K, 1%, (YEL, WHT, WHT, RED, BRN) R8-6.8K, 1/4W, 5%, (BLU, GRY, RED, GLD) Install and slder all the capacitrs: C1, uF marked (103) n2cx_accuprbe_plus_assembly_ pdf Page 2 f 12

3 C3 -.1uF marked (104) Slder D1,2 1N5711 t the circuit bard. Nte the banded end f the dide must match the silk screened band legend n the surface f the pcb. Slder U1, the LMC6482AIN Op Amp Integrated Circuit, nt the bard. Be careful t insert all the pins int the hles, it is easy t fld ne underneath. Nte the dt, designating pin 1, and insert it in the end with the silk screened ntch in the utline. Slder D3, the red LED t the designated place n the bard. The lng lead is psitive, and must g int the + hle n the silk screened legend. Slder the POWER switch S1, and RANGE switch S2, t the designated places n the bard. The perating levers g t the utside f the bard. Slder the battery hlder, where marked n the bard. Be sure t bserve the crrect alignment. The spring end, ( - ),f the hlder twards the end f the bard. Slide the plastic bt back frm the alligatr clip and slder the lead t the clip. Smetimes these are crimped nly, and can lse cnductivity. Replace the bt. Cut the 3/16 dia. x 2 L. heat shrink tubing in half and place ne piece ver the lse end f the alligatr clip lead. Slder the lead assembly t ne f the #4 ring terminals, and shrink the tubing t the transitin frm the ring terminal t the lead. Clr may vary frm picture. Set it aside fr later assembly. n2cx_accuprbe_plus_assembly_ pdf Page 3 f 12

4 File a cntact pint n ne end f the 2 lng, 3/32 brass rd as shwn. File dwn the ther end f the brass rd t accept the ther #4 ring terminal, and slder it in place. An electric drill makes it easy, but yu can d it by hand as well. Secure the cntact pint and ring terminal assembly t the signal pad f the pcb using the 4-40 x 1/4 pan head screw, lck washer, and steel nut in the rder shwn. The screw head shuld be n the bttm f the pcb, then the bard, ring terminal, lck washer, and finally the steel nut. Tighten the nut securely, checking that the ring terminal des nt tuch either f the leads f C1 r C2. Temprarily attach the alligatr clip assembly t the brass nut. It will be required fr testing, but will be remved fr final packaging. Strip and prepare as shwn, 1/2 ff ne end f the RG-174 cax cable. n2cx_accuprbe_plus_assembly_ pdf Page 4 f 12

5 Slder the center cnductr t the pad marked CENTER, and the shield t the pad marked SHIELD. Secure the cax t the pcb using the cable tie supplied Finally, strip 3 1/2 and prepare as shwn the end f the RG-174. Pass the center cnductr thrugh the side f the braided shield, as shwn. Slide the remaining piece f shrink tubing ver the end befre attaching the banana plugs. Attach the center cnductr f the cax t the RED plug and the shield t the BLACK plug, and shrink the remaining piece f tubing at the transitin. Insert the 12V, A23 battery, with the negative side twards the rear f the bard. Yu are ready fr testing. n2cx_accuprbe_plus_assembly_ pdf Page 5 f 12

6 Je N2CX has written the testing, trubleshting, and usage prcedures. Checkut: Befre cnnecting a battery fr the first time, ensure that RANGE switch is in the LO psitin. Cnnect the utput leads t a DMM, bserving crrect plarity. The red plug is psitive and the back ne is negative. Set the DMM t read DC vltage n a range f 10 vlts r s. Nw set pwer n. The DMM shuld read abut 10 mv r less. If it reads much higher than this check cnnectins and ensure that IC U1 is riented crrectly. T check peratin, yu will need a lw-level RF surce. The best way t check peratin is with a calibrated RF signal generatr. Simply lad the utput f the generatr with its rated lad resistance and cnnect the prbe acrss the resistr. DC readings n the DMM shuld be the RMS value f the signal generatr utput. Lacking a calibrated signal generatr yu can use an scillatr in a receiver. Clip the input grund lead t a grund pint in the receiver clse t the scillatr cmpnents and tuch the input prbe t the utput f the scillatr. Yu shuld get a reading in the 10 s f millivlts t several vlts depending n the scillatr utput level. If yu have a circuit where the RF levels are specified yu can verify that the readings agree. Otherwise all yu will get is a relative indicatin. If yur signal generatr utput is variable but nt calibrated yu can set it using an scillscpe. Set the utput t 1.4V p-p and the RMS value will be V. Verify that the Accuprbe indicates 0.224V. The N2CX Accuprbe s HIGH range can be checked using an HF QRP transmitter. Be sure t set switch t the HIGH psitin. Set the transmitter t utput a knwn level in the QRP range and assure that it is terminated in a 50 hm lad. Nw clip the Accuprbe Plus grund lead t a cnvenient grund pint and tuch the input prbe t the center cnductr f the transmitter utput cnnectr. The DC reading n the DMM will be 1/10 the RMS value f the transmitter utput vltage. At 1 watt this will be 707 mv, ranging up t 1.58 mv fr a 5 watt transmitter. Trubleshting Tips As usual, check fr bad slder jints, crrect cmpnent placement, dide, and U1 rientatin. If the LED des nt light, check t insure the battery is secure and is in the crrect directin. If that seems OK, then check the LED, it may be in backwards r pen. Final Assembly: D nt prceed until yu have tested and verified all is assembled and perating crrectly. The prbe assembly is encapsulated in the 3/4 diameter clear heat shrink tubing. All the perating access t the switches, cable, alligatr clip, and battery will be prvided fr. The shrink tubing is a ne time sht, s make sure yu are cmpleted and tested befre this final peratin. Make a final check that all cmpnents are trimmed n the bttm f the pcb, and remve the alligatr clip assembly used in testing. It will be re-attached later. n2cx_accuprbe_plus_assembly_ pdf Page 6 f 12

7 Slide the cmplete assembly int the shrink wrap, battery end first. Center it int the piece prvided. It gets a little tight after ging ver the tp f the ptentimeter shaft and past the mde switch. Take yur time, it will fit. Using an apprpriate heat surce, eg. heat gun, r ne f the small craft ht air surces fr ding embssed cards, start t shrink the tubing. Take yur time. Sme heat guns are extremely ht, and can strip paint, s be careful, g slwly. I prefer the craft ht air gun, it des a gradual shrink, and it s difficult t damage cmpnents. This picture shws what it lks like abut 50% thrugh the prcess. At this pint yu want t stp n2cx_accuprbe_plus_assembly_ pdf Page 7 f 12

8 Use an Xact knife, and trim arund as shwn. This picture shws after the trimming. This will prvide fr a nice finished lk when cmplete. Finish shrinking the tubing until it pulls dwn t tuch the surface f the cmpnents and the bttm f the pcb. Be careful arund the battery hlder, it is especially sensitive t verheating. Yu are just lking t insulate and prtect the cmpnents and pcb! D nt verheat. n2cx_accuprbe_plus_assembly_ pdf Page 8 f 12

9 After the shrink tubing has cled, use a razr knife t carefully trim arund the switches, s they have full travel. Carefully trim the access t the battery cmpartment, alligatr clip cnnectin pint, and arund the prbe end as needed. Attach the alligatr lead assembly with the remaining 4-40 x 1/4 pan head screw, and lck washer. The prper rder is, 4-40 screw, ring terminal, internal tth lck washer, attached t the brass nut. D nt ver tighten r yu will break the brass nut ff the pcb. n2cx_accuprbe_plus_assembly_ pdf Page 9 f 12

10 Install the battery, and yu are ready fr use. The 12v battery was selected fr it s small size. It is an inexpensive, readily available battery, used in devices like garage dr peners, etc. The assembly nly draws a few ma, but still d nt leave the pwer switch n, when nt taking measurements. Thery f Operatin The Accuprbe is an RF detectr with cmpensatin circuitry that extends accurate readings well belw cmmn RF detectr prbes. Reference t the attached schematic diagram shws that it begins with a cmmn AC-cupled half-wave detectr frmed by input capacitr C1, Schttky dide D1, resistr R1 and filter capacitr C2. At RF input levels f several vlts r mre, the DC acrss C2 is apprximately the peak value f the input signals. Hwever the inherent dide nn-linearity causes the DC vltage t be less than the peak vltage at lw levels and quite small (nly millivlts) when the input RF is belw 100 mv. Fr lw input levels (the LOW range) is used. Resistr R2 serves as a lad fr the half-wave detectr. DC frm the detectr is fed t peratinal amplifier U1a thrugh R3. R3 may appear unnecessary since its resistance is s lw that it has negligible effect, hwever it prevents damage t U1 frm input vltages higher than the specified range. n2cx_accuprbe_plus_assembly_ pdf Page 10 f 12

11 Dide D2 prvides feedback t the U1a s inverting input t cmpensate fr lw-signal detectr nn-linearity. The amunt f feedback applied is adjusted by resistr R4. This cmpensatin scheme is the brainchild f Jhn Grebenkemper, KI6WX wh used it in SWR bridges. W7EL later applied the same technique in QRP SWR bridges. Their material has appeared in the ARRL Handbk and QST. U1a s utput is the crrected peak value f the input RF vltage. It is fed thrugh a vltage divider frmed by R6 and R7 which cnvert it t the input s RMS value. Again U1b is a unity gain buffer that feeds a DMM. Fr higher vltage levels (the HIGH range) is used. Resistrs R5 and R7 frm a vltage divider t cnvert the peak DC vltage t the crrespnding RMS DC value f the RF input and reduces the vltage by 10:1. Operatinal amplifier U1b is a unity-gain buffer that feeds the resulting DC level t an external DMM and prevents lading f the detectr by the DMM. The 10:1 vltage reductin is needed s that DC fed t U1b is less than its 9-vlt pwer supply. This results in DC readings n the HIGH range that are 1/10 the RF RMS input vltage. Operating pwer is supplied by a 12-vlt alkaline battery. Capacitr C3 serves as a pwer supply bypass fr U1 t prevent instability. Usage: The N2CX Accuprbe Plus is useful fr measuring RF signals with predictable results frm 100 khz t at least 30 MHz at levels ranging frm 10 s f millivlts up t 35 V rms. It prvides minimal circuit lading s that it can be used fr signal tracing in scillatr and mixer circuits as well as multistage QRP transmitters. Several suggested applicatins are: Amplifier input and utput vltages t determine gain Filter input and utput vltages t determine lss. Measurement f resnant circuit r filter circuits acrss a frequency band t check bandwidth r Q. RF pwer levels acrss a dummy lad frm micrwatts t beynd QRP. Nte that a very accurate 50 hm dummy lad is needed t retain accuracy. Attenuatr calibratin by accurate lss measurements. Signal generatr utput calibratin Credits: The N2CX Accuprbe Plus prject was cnceived and prmted by Dug, KI6DS wh als prvided necessary prdding and encuragement. Printed circuit layut was carried ut by Ken, WA4MNT. Circuit design and checkut was perfrmed by Je, N2CX. Technical questins n the N2CX Accuprbe Plus can be directed t him at n2cx@verizn.net n2cx_accuprbe_plus_assembly_ pdf Page 11 f 12

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