QRP Base Station Accessory (QBSA)Steven weber, KD1JV

633 Champlain St, Berlin, NH 03570kd1jv@moose.ncia.net http://kd1jv.qrpradio.com

The QRP Base Station Accessory is designed to enhance the use of the AT Sprint series rigswhile at home. The digital dial provides direct reading of the operating frequency for all bands, theRF power meter can display either forward or reverse power up to 9.99 watts, the 2 watt audioamplifier is used to drive a speaker when headphones are not wanted and the 6 to 11 volt variableregulator provides a means of adjusting power output of the rig.

While designed primarily for use with the AT Sprint rigs, the QRP Base Station Accessory can beused with other QRP rigs as well. The IF offset for the digital dial can be programmed and pinselect inputs can be used to set how the IF offset is used with the VFO frequency to produce acorrect, direct reading dial. The QBSA might also find a home on the work bench, as the functionsfound in the unit can be handy there too.

Operation:

Operation is simple. There are two controls, one for the variable voltage regulator located to theleft of the display and the other, to the right of the display for the audio amplifier volume. Amomentary contact switch centered under the display selects display modes for indicatingfrequency or RF power.

Display modes:

There are four display modes selected by the Function switch. The QBSA powers up in thefrequency display mode, showing kHz and the 100 Hz digit. [060.0] This would be your nominaldisplay mode. Only the kHz digits are needed, as the MHz digits are implied by the band youroperating on. If you forgot which band the rig is set to, the MHz digits may be displayed by clickingand holding closed the Function button for about 1 second. In MHz display mode, the decimalpoint shifts one place to the left. [14.06] To return to kHz display mode, hold the Function buttonclosed again for 1 second.

IF Offset:

In order for the display to show the actual operating frequency and not just the localoscillator frequency the QBSA needs to know what the IF frequency is. Once that is known, it canbe added or subtracted to the LO frequency. There is a third possible combination, which is theLO subtracted from the IF, which is a reverse tuning VFO. The ATS rigs do not use thiscombination, but it can be selected for rigs which do. The DDS oscillator in ATS rigs generateboth the LO and transmit frequency. In order to keep the frequency display from becoming being“jumpy” while transmitting, the current displayed frequency is frozen as soon as power output isdetected by the power meter. Therefore, the antenna output of the ATS rig must be connected tothe antenna through the power meter to keep the display stable during transmit. There is a shortdelay built in before frequency counting begins again after power output drops to zero. At slowcode speeds, this delay might not be quite long enough to keep the display from showing arandom count until there is a long enough pause to get a proper LO count again. Rigs in which theLO does not change during transmit will not have this problem and don't need to be connectedthrough the power meter if not desired for some reason.

Programming IF offset frequency into QBSA memory:

The IF frequency is entered into the QBSA simply by using the counter to measure it. In the caseof the ATS rigs, the calibration mode built into the rig can be used to both calibrate the counterand then to generate the IF frequency, using the DDS signal from the rig.

For rigs other than the ATS series, the counter would be connected to the BFO oscillator.This is usually set 600 Hz higher or lower than the actual operating frequency. If a trimmer tochange the BFO frequency is available, it should be reset to produce a zero (0) Hz beat noteinstead of the normal 600 Hz tone for entering the correct frequency into the QBSA. Once this isdone, reset the trimmer back to produce the normal 600 Hz beat note.

Programming steps:

1. Connect counter input to rig as described above.2. Confirm proper BFO frequency on display.3. Make sure there is no jumper in place at either the “ATS” or ENOS” pins on the main board. IF

offset store mode can not be entered if the offset is enabled by one of these two jumpers.4. Click and hold closed the Function switch for 11 seconds.5. Release the switch when [ IF] appears on the display. The switch must be released within 5

seconds of this message appearing, or a “stuck switch” condition will be assumed. 6. When the switch is released, the BFO frequency is stored in EEPROM for use as the IF offset.

The display will go back to showing the input frequency to the counter. 7. To enable the IF offset, jumper either the “ATS” or “ENOS” pin to ground.

There are two rows of four pads on the main board which are used to enable and select the IFoffset options.

If the ATS and ENOS pads are left open, the display will alwaysshow the actual input frequency to the counter. Putting a jumper between the pads labeled “ATS” tells the QBSAthat an ATS rig is being used. Putting a jumper between the padslabeled “ENOS” (enable offset) allows use of the pad select IF offsetdirections, which are the remaining two sets of pads.

When the “Live” ENOS pad is grounded: Grounding the “Live” +/- pad selects LO-IF function. Left open, LO+IF function is performed.Grounding the “Live” REV pad activates IF-LO function, regardless of setting of +/- pads.

When used with the ATS series rigs, the frequency display needs to use LO+IF on the 40to 20 meter bands and LO-IF on the 80m band. The QBSA will automatically detect which band isbeing used and use the appropriate arithmetic.

For rigs other then the ATS series, you have to tell the QBSA which arithmetic function touse. This is done with setting the jumpers as described above. If the QBSA is to be used withsingle band rig, this jumper setting can be hard wired. Or it can come out to a switch if it needs tobe changed for use with a multi-band rig which uses different mixing schemes on different bands.

Power meter functions:

Forward Power:

A short click of the Function switch changes the display to indicate forward (output) power. InForward power display mode, the most significant digit blanks and the decimal point moves onedigit to the left [ 0.00] If power input exceeds 9.99 watts, the display will change to [ -. - - ].

The reflected power mode has to be selected before the display will return to frequency readoutmode.

Reflected power:

Clicking the Function switch again changes the display to indicate reflected power. The switchmay have to be held closed for a second or so to respond. When the display changes to reversepower mode, an “r” will appear on the most significant digit location. [r0.00]

Reflected power is shown instead of SWR. Therefore, when adjusting an antenna tuner for bestmatch, it should be adjusted for no (zero) reverse power. This would correspond to a 1:1 SWR. Ifyou want to know the SWR for some reason, it can be calculated easy from the forward andreflected power readings. (Though its a somewhat cumbersome formula)

Clicking the Function switch while in the reflected power display mode will return to the Frequencydisplay mode.

Packaging and parts not supplied:

The QBSA was designed to fit into a NorCal BLT case. Unfortunately, these cases are no longeravailable separately from the complete BLT kit. If you happen to have one of these BLT casesyou'd like to use, please note that the X1 crystal and trimmer cap would have to be mounted onthe bottom of the board and the display mounted with the right angle SIP pins mounted to thedisplay with the bent side of the pins mounted to the front side of the display board. This reducesthe overall length of the assembled boards so that it will fit inside the BLT case. These mountingdetails are explained later in the assembly section.

A possible cabinet would be a 3” x 4” x 1.5” BUD “converta box” (Mouser part # 563-CU341A,$11.70) A larger cabinet could be used if you wanted to include an AC supply, speaker or otheraccessories in the same box. In these cases you might not be able to use the board mountedRCA RF jacks unless the display is connected to the main board with a ribbon cable. The QBSAcould also be made to fit into a small LMB sloping panel box. Though this will take some ingenuityto mount the display. A couple of mounting holes could be drilled into the display board below thecontrols. Some ribbon cable would definitely be needed to connect the display to the main board.

A drill template in bit map formate is included on the CD. This will print to scale if opened andprinted from MS paint. Cutting the display opening in the cabinet can be a chore. One method isto drill rows of small holes, break out the middle and clean up the edges with a flat file. Thequickest and easiest method I've found is to use a Dremal cut off wheel. One needs to be carefulthough, as these shatter easily. Be sure to wear eye protection and a dust mask so you don'tinhale the fine dust made in the process.

All board mounted parts are included in the kit, along with a 3.5mm mono jack for plugging aspeaker into, 18” of RG-174 coax to connect the counter to the rig and a piece of red filter film toput over the display. The coax is supplied so your not tempted to use something less suitable andthe red filter film makes the display look better.

Parts you will probably need:

DC power jack and plug to match what ever you use as a “standard” in your gear.(Jacks -2.1 mm Metal Chassis mount Mouser # 163-4304, $2.10, 2.5 mm # 163-4305, $2.04)(Plugs – 2.1 mm 1710-2131,$0.65 , 2.5 mm # 1710-2510, $0.57) RCA plug and jack for counter connection to rig. Panel Mount RCA jack, Mouser # 161-1002,Plain RCA Plug, #17PP050, $0.21, Plug with red shell, # 174-0551-E, $0.56)

Extra .7 mm power plug for ATS rig. (Mouser # 171-3218-EX $1.22)

Stereo plug and cable for audio input. (Using plug and cable from cheap ear buds works well)

The frequency counter input cable and audio input cable can be hard wired to the circuit boards.This eliminates the need for a couple of jacks on the back of the cabinet and plugs on the wires.

Small TO-220 heat sink Mouser # 567-290-2AB ($0.38)TO-220 insulating mounting kit Mouser # 532-4880 ($0.77) (Only needed if mounting regulator tochassis.)

Mouser 1-800-346-6873 No minimum order.

Flex cable assemblies, .1” spaced socket one end, solder pins the other. These are only availablefrom Digi-Key, which has a $5.00 fee for orders under $25.00 1-800-344-4539

2” lengths – 6 conductor A9BGA-0602F-ND $3.27 , 8 conductor A9BAG-0802F-ND $3.90(longer lengths available in 1” increments. These cables are only needed if you don't want tosolder the display board directly to main board)

Parts list:Location Value code location value type

R1 100 1%, 1206 1000 C1 .1 uF 0805

R2 100 1%, 1206 1000 C2 .1 uF 0805

R3 100 1%, 1206 1000 C3 100 uF/16V Alum electro

R4 100 1%, 1206 1000 C4 .1 uF 0805

R5 47 K 5% 0805 473 C5 4.7 uF/16V Alum electro

R6 4.3 K 5% 0805 432 C6 22 p 0805

R7 22 K 5% 0805 223 C7 47 uF/16V Alum electro

R8 47 K 5% 0805 473 C8 330 uF/16V Alum electro

R9 22 K 5% 0805 223 C9 .1 uF 0805

R10 10 K 5% 0805 432 C10 .1 uF 0805

R11 820 5% 1/4W GRY/RED/BRN C11 3.3 uF/50V Alum electro

R12 10 K 5% 0805 103 C12 .1 uF 0805

R13 4.3 K 5% 0805 432 C13 .1 uF 0805

R14 220 5% 1/4W RED/RED/BRN C14 .1 uF 0805

R15 1 MEG 105 C15 22 p 0805

R16 2.2K 5% 0805 222 C16 .1 uF 0805

R17 100K 5% 0805 104 C17 22 uF/6.3V Alum electro

R18 1K 5% 0805 102 C18 .1 uF 0805

R19 SKIPPED C19 30p trimmer

R20 SKIPPED Display brd 1 uF/25V Alum electro

R21 1K 5% 0805 102 D1,2,4,5 SD101C Fast shottky

R22 1K 5% 0805 102 D3 1N5231B 5.1V, 500 mw

R23 1K 5% 0805 102 D6 1N4007 Si rectifier

R24 1K 5% 0805 102 Q1 MMBFJ310 N-JFET

R25 1K 5% 0805 102 Q2 MMBT5911 RF NPN

R26 1K 5% 0805 102

R27 1K 5% 0805 102 U1 LM358 Dual LP op amp

R28 1K 5% 0805 102 U2 LM380-8N 2.5W audio amp

V1/2 1 K trimmers U3 MEGA48 Atmel CPU

V3 50 K 9mm pot Audio U4 7805 +5V TO-220

V4 1 K 9mm pot Linear U5 LM317T Adj reg TO-220

L1 4.7 uH 1206 chip U6 74HC4017 Decade counter

L2 10 uH 1206 chip Display 4 digit multiplex Common anode

X1 10.000 MHz HC-49/US

PC mount RCA jacks (2) PC boards Main/display

RT angle SIP 8/6 pins S1 6mm X 13mm TACT Switch

SMT solder 2 feet Mag wire Teflon wire

4- #2 screws 18” RG-174

4- #2 swag 1/4” spacers Red filter

Assembly:

Separate the display board from the main board by gently snapping it on the scored line. Insert theboard mounting stand-offs in the four corner holes of the main board. Run a bead of solder around the edgeof the spacer collar, which sticks out a little on the top side of the board. This will secure the spacer to theboard. SMT parts are installed first, starting with the bottom side of the board. Resistors have their values markedon them. The part carrier for the caps have been color coded with a marker and inductors by a color stickerto identify them. The same with the transistors, since their markings are hard to read.

Bottom surface mounted parts:

-------------------------------------------------------------------------------------------------------------Top surface mounted parts

Pin 1 goes towards notch on board screen outline. Pin 1 always lowerleft corner when part number reads left to right. Beveled edge ofpackage always Pin 1 side. Manufactures logo (if printed on part) isalways at Pin 1 end.

location value markings COLORR15 1 MEG 105

R16 2.2 K 222

R17 100 K 104

R18 1 K 102

L1 4.7 uH NONE YELLOW

C6 22 p NONE ORANGE

C9,10,18 .1 uF NONE BLUE

Q1 MMBFJ310 Pink

Q2 MMBT5911 Green

U6 74HC4017 74HC4017 Decade counter

location value markings colorR1,2,3,4 100 1% 1000

R5,R8 47 K 5% 473

R6,R13 4.3 K 5% 432

R7,R9 22 K 5% 223

R10,R12 10 K 5% 103

R21-28 1 K 5% 102

C1,2,4,12,13,14,16

.1 uF CAPS none BLUE

C15 22p CAP none ORANGE

L2 10 uH none PINK

Through hole parts:

C19 and X1 installed later.

U4 mounting:

Be sure the tab side of the regulatorfaces towards the D6 diode

U5 mounting:

U5 can be mounted in one of two ways. First option is top side mounting, as shown in layout. (Make surethe tab faces the R14 resistor) It may also be mounted on the bottom side of the board, so that it can beheat sinked to the cabinet. Using this option, insulating hardware must be used between the tab of thepackage and the cabinet. (not supplied) See drawing below. Heat sinking is not required if using thevariable supply regulator to power the ATS series rigs. If the supply might be used to power higher currentrigs or accessories, then heat sinking is recommended. A small heat sink could be bolted to the regulator ifit is mounted top side.

Location value Markings

R11 820 ohms GRY/RED/BRN

R14 220 ohms RED/RED/BRN

D3 5.1V zener 1N5231B loose

D1,2,4,5 SD101C On tape

D6 1N4007 Black plastic

Cal trimmers 1 K 102 (two places)

C3 100 uF/16V Long lead +

C5 10 uF/16V Long lead +

C7 47 uF/16V Long lead +

C8 330 uF/16V Long lead +

C11 3.3 uF/50V Long lead +

C17 22 uF/6.3V Long lead +

U1,2 8 pin socket

U3 28 pin socket

U5 LM317T See text for mounting

U4 7805 5V regulator

Winding the balun core:

Ten (10) turns of magnet wire are wound in each of the two holes in the core. Phasing isimportant for proper operation. Windings are started on opposite sides of the core, as shown inthe diagram. Position the turns along the sides of the core as shown. Wind 10 turns on each sideof the core. In this case, one turn is a single pass through the inside of the core. When finished,there will be nine (9) turns showing on the outside of the core.

Mounting the core:Position the core so that the windings which start at the bottom of the core are next to the twocenter row of pads on the core outline. Trim and tin the magnet wire and solder into these twoholes. Solder the windings which come out from the fop of the core to the pads shown in thediagram.

Cut, strip and tin the #22 Teflon insulated wire and install as shown. The Blue lines in the diagramabove show the location of these wires, which of course, run through the hole in the core. Thepicture below shows how it should look when done.

If you wish to use the board mounted RCA jacks, they can be installed now.

Assembly of the main board is now complete.

Display Board:

The LED display, the two controls and the switch are mounted on the side of the display boardlabeled “FRONT”. The printing on the board is upside down.

Mount the display first. It is installed correctly when the digits slant slightly to the right and the fourdecimal points are along the bottom (towards the switch). See diagram.

Now install the two controls. Note they have different values. The one marked “B1K” goes to theleft of the display and the one marked “A50K” goes to the right of the display. (Value marked onside of control opposite pins) Use your pliers to remove the kink in the mounting tab which will gointo the hole next to to the display. The control will fit real snug to the side of the display. Now install the switch. It will only fit one way.

A 1 ufd electrolytic cap is soldered to the back side of the display board at the capacitor outline,next to the 50K control.

Final assembly, Display board mounting:The diagram below shows the two options for mounting the display. The alternate method requiresmounting C19 and X1 on the bottom of the board. Mounting the display in this way allows use of a 3.00”deep cabinet.

Once you decide how the display board will be connected to the main board, solder C19 and X1 in place onthe appropriate side of the board. If C19 and X1 are mounted on the top side of the main board, install theSIP pins on the main board, with the bent pin in the main board, like this:

If C19 and X1 are mounted to the bottom side of the board, the SIP pins need to be first installed on thedisplay board, with the bent pins in the display board. See diagram above, on right.

A jumper needs to be added to the board as shown in the diagram above. The blue line indicates the addedjumper. The wrong pad on the switch was connected to ground on the layout, causing the switch to alwaysbe “closed”. The tracks have been cut for you, so all you need to do is add the jumper. You better doublecheck that the ground tracks have been cut on the upper right switch pad!

Now mate the two boards. Before you solder more than one pin, make sure the display board issquare to the main board.

Once the display board is soldered into place, use the two conductor ribbon cable to connect thecontrols to the main board. The wires connecting to the VADJ control go straight back to the holeslabeled “VADJ” on the main board. The cable will have to be twisted 180 degrees, otherwiseclockwise turning of the control will make the voltage output go down, not up. The cableconnecting the volume control to the main board has a half twist in it. Be sure to connect the holeslabeled “G” on both boards together. See picture below.

The completed boards.

External connections:

The only one which might not be obvious is the audio in. The audio in cable is connected at theback of the display board, behind the volume control.

Initial test:

Before installing the IC's, connect power to the board (12 to 14 volts) and make sure there is 5volts on Pin 1 of U3. You can also test the operation of the variable regulator. The output voltageshould vary between about 6 and 11 volts. The upper end of the voltage range will depend on thesupply voltage. A DC input voltage of about 14 volts is needed to get the full range. If this is OK,remove power and insert the IC's. ( U1 - LM358, U2 – LM380-N, U3 – MEGA48) Now, when youreconnect power, the display should come on and show all “8's” for a few seconds. Then thedisplay will go to all “0's”.

Frequency calibration: (Using ATS rig)The calibration feature of the ATS rigs can be used to calibrate the counter and set the IF offsetvalue. Since the ATS rigs load default values when calibration mode is entered, this means youwill have to recalibrate the ATS rig at the same time, that is if you had calibrated it.

1. Connect the input of the frequency counter to the output of the ATS DDS filter, using thesupplied 4.7 pF cap, at the rig end of the cable. This ensures the capacitance of the cabledoes not load down the DDS filter and affect its operation.

Picture of 4.7 p cap between output of DDS filter and new RCA jackfor connection back to QBSA counter. It would be a good idea to colorcode the RCA plugs going to the rig, so you don't plug the counter intothe antenna jack and visa-versa.

2. Power up the QBSA and the ATS rig in its calibration mode. 3. If one is available, use an accurate frequency counter to set the output of the DDS to exactly

10.000,000 MHz, as explained in the ATS manual. If no counter is available, assume theoutput is pretty close to 10.000000 MHz and skip to next step.

4. Adjust the Green trimmer on the accessory board so the display reads [000.0] The modeswitch can be used to shift the display so that the MHz digits are displayed, by clicking andholding closed for a second. The display should read [10.00]. If not, there is a problem withyour connections.

5. Advance the ATS rig cal mode to IF offset calibration mode. 6. Tweak the IF frequency of the ATS for optimum as explained in the ATS manual. Confirm the

IF frequency is being displayed on the QBSA. When your ready to store the IF frequency intothe QBSA, hold the function button closed until [IF . ] is displayed and release the button.(about 11 seconds. The switch must be release before 5 more seconds passes, or it willassume a “stuck switch” condition). The frequency is now stored as the IF offset.

7. To activate the IF offset, a jumper must be placed across the pads labeled “ATS” on the mainboard. You can do this on the bottom side, as the pads are a bit easier to get to on that side.

RF Power Calibration:Connect a rig to the transmitter jack and a 50 ohm dummy load to the antenna jack. Power up the BSA. Click the Function switch to change the display to forward power mode. Whenthe display is showing forward power the most significant digit blanks, and the decimal point shiftsone position to the left.

If your are using an ATS rig, you can use the variable voltage regulator to adjust the power outputof the rig to exactly 2 watts. This is determined by measuring the voltage at pin 1 of U1 with aDVM and adjusting the power out of the transmitter until the voltage at this pin is 1.414 volts. Nowadjust the trimmer labeled “FWD CAL” so the BSA display reads [ 2.00].

To adjust the reverse power, swap the antenna and rig connections at the BSA board, so that therig is plugged into the antenna jack and the dummy load to the transmitter jack.

Switch the display to reverse power mode by clicking the function switch. You might have to hold itclosed for a second, as the switch is not poled by the processor during A/D conversions and whendoing the calculations. When reverse power is displayed, the most significant digit will show an 'r”so the display should look like this: [r0.00]

Key the transmitter again and verify there is also 1.414 volts on pin 7 of U1, or close to it. Theremaybe some minor variation due to the exact offset voltage of the op amp input in respect to theone use on the forward detector side and the forward drop of the detecting diodes. Now adjust the“REV” trimmer so the display again reads [r2.00]

Un-key the rig and calibration is complete.

If a rig with variable power output is available, calibrating at the highest power level available up to9 watts is better. Here is a table of the voltage at pin 1/7 of U1 which correspond to power levelsof 1 to 9 watts:

Power voltage power voltage1.00 watt 0.9998 V 6.00 watts 2.449 V

2.00 watts 1.414 V 7.00 watts 2.828 V

3.00 watts 1.731 V 8.00 watts 2.828 V

4.00 watts 1.999 V 9.00 watts 2.999 V

5.00 watts 2.235 V

The coupler transformer is a current transformer with a 1:10 turns ratio. Since the load on thesecondary of the transformer is the same as the load on the primary, the voltage across thesecondary load is 1/10th that which is across the primary load. By calculating the peak voltageacross the primary load for various power levels and dividing it by 10, we get the voltage which willbe developed across the secondary load, which are shown in the table above.

Alternative method of calibration:

It is possible to use the variable voltage regulator to calibrate the power meter. The anode (coilside) of the detector diodes D1 and D2 have to be lifted off the board, other wise the secondarywinding on the transformer will short a DC voltage to ground. Since the output of the variableregulator only goes down to about 6 volts, a voltage divider also needs to be added. A 2.2K and1K resistor would do. Now you can adjust the regulator to produce one the voltages listed in thecalibration table on the outputs of U1.