Mounting/Testing Ham Radio Board 1

The following text describes how to put the receiver together as shown on the Home Page. If you have a problem when testing the boards, go to "LED Diagnosis/Troubleshooting" for help.

A Bottom Plate is not needed unless you install a transmitter amplifier as part of the BLT and want to place it below the BLT.

Instructions if drilled bottom plate is wanted with the kit.

With the 6-32 size hardware supplied with the kit the holes need to be enlarged with a 9/64" drill bit. The holes are originally drilled for 4-40 size hardware.

____Spacers (that use 6-32 hardware) are supplied with the kit. Four male/female spacers 1-1/4" long are used underneath the board with the male end going through the PCB.

A female/female 1-7/8" spacer is mounted on top of it. When Board 2 is finished, it is held with screws on the top of the 1-7/8" spacers at each corner.

Install rubber feet on the bottom of the spacers if wanted.

The holes at these locations have been drilled with a 9/64" drill bit to accommodate the 6-32 hardware. All other mounting holes are 1/8" that accommodate 4-40 hardware.

____The minimum mounting holes is 4, one on each corner. If you use additional mounting holes and you use 6-32 hardware, but sure to enlarge the holes with a 9/64" drill bit.

Board 1 is divided into three sections, each with holes at each corner, so one could cut the boards on the lines of holes and mount them separately in a different design. One connection between Section 1 (VFO/ Amplifiers) and Section 3 (First Mixer/Crystal Filter) is VFO Out and VFO In.

There is one connection between Section 2 (RF Amplifier/Bandpass Filter) and Section 3 with the boxes labeled Input Out and Input In at the front between the boards. They are connected together with traces that run between the sections unless the boards are separated at the holes defining the sections.

These connectors are not supplied with the kit. The prototypes used RCA connectors that were soldered to the board. Lightly scraping the green solder resist will reveal a ground plane that can be soldered to.

Connectors can be mounted to a bottom board with right angle brackets or a 1 x 8-1/2" aluminum plate mounted vertically across the back between (or below) the boards and tied to the spacers.

The Speaker connection is on Board 2.

The LCD display board should not be grounded to the receiver. It causes a ground loop that introduces oscillator noise from the display into the receiver.

Also, a piece of high temp aluminum tape has been placed over the larger round chip which is the source of the noise. See below:

To eliminate this problem the display is held by two small plastic ties to the bottom of Board 1. It needs a fairly good upward angle toward the operator.

To achieve this, the square hole for the tie (black arrows) is placed as shown below so it can help angle the display upwards. The PCB holes the ties run through are shown with the yellow arrows.

The top of the ties are looped through the holes of the display and then through the square holders of the ties.

Attach the cables, Pin 1 to Pin 1 and Pin 16 to Pin 16. The masking tape on the cables on the right are labeled 1 and 16 to help get the cables on correctly.

Testing Board 1

DDS VFO/VFO Amps/Bandpass Filter || Bandpass Tuning Pot
First Mixer/Post-Mixer Amplifier || Crystal Filters

If you are using a 13.8 volt power supply, use three 1 to 3 amp (supplied) diodes to drop the voltage to a little below 12 volts. The bands of the diodes are oriented toward the receiver 12V connection. The receiver works best at 11.5 to 12 volts.

DDS VFO/VFO Amps/Bandpass Filter

If the 40/30/20 LED at the Bandpass Filters is bright/dim, shield any light (overhead shop light, etc.) that is hitting the Photodiodes. The 40/30/20 LED should go out.

____Move the Bandpass switch to the 40/30/20 side, the LED at the 40/30/20 filter should turn on.

If the 17/15/12/10 LED at the Bandpass Filters is bright/dim, shield any light (overhead shop light, etc.) that is hitting the Photodiodes. The 17/15/12/10 LED should go out.

Troubleshooting

Bandpass Tuning Pot

Troubleshooting

First Mixer/Post-Mixer Amplifier

To test this and show its function, turn the 500K trimmer at the 1st MOSFET amplifier counterclockwise and the LED should become dimmer or almost go out. Turn it clockwise and stop at the point right before the LED reaches maximum brightness. This adjusts the mixer drive for best dynamic range.

____VFO Post-Mixer Amplifier: The LEDs of the two Post-Mixer Amplifiers should be on. The reason for the different intensities of the LEDs is that they were different colors. They have a forward voltage drop of 1.7 to 2 Volts. Note: Do not put Super Brights in the Mixer or Post-Mixer amplifiers that have a 3.5 to 4 forward voltage drop. They will reduce gain considerably.

Troubleshooting

Crystal Filters

This is a special circuit that uses a series/shunt configuration to provide better isolation of the cyrstal filters than using two series LEDs.

The bottom LED is the series LED and lets the signal pass to the filter which is ON. The top LED is the shunt LED and shorts the signal to ground for that filter which is OFF. The series LED of one filter is connected to the shunt LED of the other filter.

____Move the Crystal Filter Switch (front of board) to Filter 1.

____Move the Crystal Filter switch to Filter 2.

Troubleshooting

If you did the adjustment with the Mixer LED brightness above, you do not need to use the instructions below. If you have an oscilloscope, it is worth while to check it. You can run the mixer above the 4 Volt P-P suggestion. You will have more gain in the receiver and more output for a transmitter, if needed.

Voltage Adjustment

With Board 1 and the DDS VFO mounted and powered up, set to 40 Meters (7.000 MHz), measure the voltage between Gate 2 of the MOSFET and Ground. Adjust to 3.60 Volts with a Red LED, to 5.10 with a Blue LED.

This is not a super critical adjustment, anywhere close will be fine. Is is important to do this measurement on 40 meters (7.000MHz) as the voltage on the other bands will vary quite a lot.

With a Oscilloscope

The screen shows the output for 7MHz (4 volts peak to peak). The output remains fairly flat all the way to 28MHz. There will be a very slight drop at 24MHz to 28 MHz. Best sensitivity is at 8 Volts P-P, (set on 40 meters). This is the level set with the above instructions.

Noise peaks should be heard on all the bands with a tuned antenna for the band. At 8 Volts P-P, you may see the sign wave be flat at the bottom, this is OK, just clipping in the mixer.

The receiver has good gain down to 4 volts peak to peak with good noise peaks on 80, 40, 30 and 20 Meters, which is the setting for best dynamic range. However, for good noise peaks on the higher bands, an 8 Volt P-P (set on 40 meters) will have very good sensitivity on 17, 15, 12, and 10 meters. The only difference will be higher noise levels on the lower bands, because of the better sensitivity.

The 8 volts P-P will drive any old boat anchor tube transmitter. With the modern QRP transmitters, you may need a pad to keep them from being over driven. A 6dB pad would be a good starting point if you don't have an oscilloscope to measure the drive from the receiver.

With 50 to 100 Watt amplifiers, you might need a small amplifier to bring the output to the required 1 to 2 watts. This is sometimes a problem because finding a small amplifier with flat output from 40 to 10 meters is difficult. This problem is addressed in the transmit page with an MRF237 amplifier.