Six Meter Operation with the BLT

The basic modifications are a Six Meter pre-amplifier, a change to a one crystal filter (26.640 MHz), a board with a MPS430 to change the crystal oscillator for a second mixer 455 kHz output, a special 16F628 for the PICEL DDS VFO with changes in the band tables for Six Meters and the offset for the 26.640 MHz Crystal Filter.
The 16F628 can only handle 12 Bands, so the 160 band is removed when the 6 Meter band is included.

Six Meter Pre-amplifier

The input Lowpass Filter has a cutoff frequency 30 MHz so it does not pass 50 MHz signals. Attempts raising the frequency to 54 MHz were not successful. Also, it was determined that an input amplifier was needed with the 6 Meter dipole that was built for this project.

The circuit above was built, installed and the receiver heard 6 Meter signals when the band was open.

A switch was used (in the photo) to change from the Low Pass Filter and the 6 meter amplifier. There is an extra Antenna input on the board (shown below) so a separate Antenna connection could be used for the 6 Meter pre-amp and that switch eliminated.

The pre-amp uses 12 Volts and is tied to a 12 Volt box next to the 2N5109 RF amp as shown above.

Building the Pre-amp

High megohm resistors (one end soldered to ground) were used as tie pads at the input, output, and 12 Volt connections

The shield is just a small square of PCB with a 1/8" or 3/16" hole drilled through it.

When mounting the 40pf trimmers, but sure you check the trimmer screw and see which connector is attached, so you can solder that one to ground. That way your trimming tool will not effect the tuning.

There should be a good peak when tuning. Use a 50 MHz signal from a signal generator or from the DDS VFO to drive the amp for tuning. If using the DDS VFO, use the 200 kHz Band that is a signal generator without the offset.

Bandpass Filter Varicap Change

When you build the 17, 15, 12, and 10 Meter Bandpass Filter, you install SIPS at the places for where the varicaps are installed on the board. The SIPS with the kit will be black in color, as the white ones (in the picture above) had holes too large for a tight fit with the varicaps. The varicaps for the 17 to 10 Meter bandpass filter are MV2115 which are 100pf varicaps.

For 6 Meters, the varicaps are changed to 50pf varicaps. There will be a couple numbers (H65 and H66) that will be supplied, but most of them will be H66. That is the only Ham Band it will tune and is about at the middle of the range, right between the 12/40 markers (at the large mark right above 30) on the Bandpass Tune Label.

The picture above shows the 50pf varicaps installed in the MV2115 locations. Please notice the flat of the varicaps and that it is installed correctly as shown by the footprint of the device.

Shown below is from AADE Filter Design showing the effective gain and tuning of this filter for 50 MHz and note it peaking at 20pf for the varicap values.

Crystal Filter Modifications

A one crystal filter is used with a 26.640 MHz crystal. The reason for this high a crystal is that there are fewer birdies in the band and the loss is less through this crystal versus the 3.546 MHz crystal. At 50 MHz losses in all the circuits to the IF strip are minimized.

The 3.546 MHZ filter also had too many birdies.

Since CW operation in the 6 meter band is not intense, the one crystal filter worked well.

Crystal Oscillator Modifications

A MPS430 Texas Instruments chip is used to generate a single frequency for down converting the 26.640 MHz frequency from the Crystal Filter to 455 kHz for the IF strip.

It is a cheap and easy construction project that comes from the 2017 September/October QEX article, "Programming the DDS AD9850 Signal Generator Module with the Texas Instruments MSP430 LaunchPad".

One important thing I found is to set the 3.3 volts from the LM317T before putting the MSP430 or the AD9850 DDS module on the board.

The MSP430 Launch Pad can be found for around $10 and includes the MSP430G2553 chip that is used in the project. A separate board was designed with the MSP430G2553 chip generating the code to run an AD9850 DDS China board.

The Code Composer 9.3.0 IDE is downloaded for free off the internet from TI and is used to load the program into the Launch Pad and chip for use on the board.

I redesigned the board for easy construction Manhattan style with an additional MMIC amplifier to give enough drive with the Crystal Oscillator Amplifier to drive the Second Mixer. The MMIC amplifier is a house numbered 1651, but any of the MAR amplifiers MMICs will work. Note that the pinout of the MAR MMICs are different from the 1651.

The reset switch was not installed on this board.
Be careful when soldering up this board. Double check that you get Pin 16
soldered correctly to the reset trace. It is too easy to make a mistake here.

The following picture is from the article (2017 September/October QEX, "Programming the DDS AD9850 Signal Generator Module with the Texas Instruments MSP430 LaunchPad") and gives another way to make the layout. Groves are cut into a single sided or double sided PCB and then the parts are soldered as shown in the picture.

When you order this kit, you will get the MPS430 already programmed for the crystal oscillator frequency. You won't need to buy the Launch Pad development Tool used to program the chip.

Any frequency can be programmed in the MPS430, see the article for information, so any crystal value can be used in the crystal filter if you so desire. The information is in the article in the link above.
The output will need an amplifier with a MMIC to drive the crystal oscillator amplifier with enough drive for the mixer. Adequate drive is shown by the LEDs in the mixer, medium to brightly lit.

The pictures above came from the article programmed for 7.045 MHz.

The picture below shows the board mounted on the BLT. It is held down on the top Board with a screw or spacer at the corner and with a screw/nut on the other end of the board with a solder lug.

The 12 volts is brought from the 12V connection on the receiver board. The output of the circuit is tied to the 39pf cap that goes to Gate 1 of the MOSFET crystal amplifier. The far end of the 39pf cap is unsoldered and lifted to tie to the output of the MPS430 circuit as shown below.

If you check the 3.3 volts, be sure to take out the MPS430 chip and the DDS so you don't blow them during the adjustment.

If everythng is working properly, the LEDs at the second mixer should be moderately to brightly lit when the receiver is powered up.

6 Meter Transmitting

6 Meter Lowpass Output Filter

This lowpass filter comes from the article "Compact 300 Watt HF Amplifier", QEX January/February , 2021 page 4. It is a half wave lowpass filter, input and ouput are 50 ohm impedance levels.
It was difficult to find a designed 6 Meter lowpass filter, so this was a welcome find in QEX.

You would use this if you are using a homebrew 6 Meter amplifier. It is not needed for the Mitsubishi M57735 described below. The Mitsubishi M57735 has a built in lowpass filter.

10 to 14 Watt 6 Meter RF Amplifier

The information for this 6 Meter amplifier comes from "Experimental Methods in RF Design", by Wes Hayward, W7ZOI, Rick Campbell, KK7B, and Bob Larkin, W7PUA, ARRL 2003, page 6.86.

Beginning at "Transmitter Power Change", it first notes a RF power chain and then talks about the Mitsubishi M57735 hybrid integrated circuit, with a power output of 14 Watts. M57735 also includes a built in low pass filter that is built on a flange that bolts to a grounded heat sink.

The M57735 can be found at UtSource for $31.72 plus shipping.

Another source is AliExpress for $26.00 plus shipping. This is where the one below came from:

Building the MM57735 Amplifier

Shown above are the items you need to build the amplifier. An aluminum heatsink and some 2" wide single or double sided PC strips. They will need to be screwed down onto the heatsink as shown above to complete the schematic.
The basic parts list:
____ 1 - MM57735 amplifier module. Also contains a low pass filter at the output.
____ 15 - .01 small capacitors, used in place of the 22pf capacitors, 4 per each 22pf, plus the one .01 shown in the schematic. Total of 5-.01s on each lead.
____ 1 - 12" length of #22 enamel wire
____ 1 - .1 pf capacitor
____ 1 - 22 mfd electrolytic capacitor, 50 volt
____ 1 - .22 mfd capacitor
____ 1 - LM317T regulator
____ 2 - 2N3904 transistors
____ 1 - IN4006 diode
____ 1 - 240 ohm 1/4 watt resistor
____ 1 - 1.5K 1/4 watt resistor
____ 2 - 2.2K 1/4 watt resistor
____ 2 - 6.8K 1/4 watt resistor
____ 1 - Small DPDT relay, as shown in the picture or similar

Schematic below:

____ First, install 5 small .01 capacitors on each of the three center pins. These are bypass capacitors for those pins.

____ Build the coil show above, 8 turns, #22 wire, on a 1/4 inch form. A screwdriver with a 1/4" shaft can be used.

____ Use a .1pf capacitor as a standoff, one pin to ground and one standing up to use for a tie point for one end of the coil. This is the tie point for the +12 volts and the red lead going to Pin 4 as shown in the picture.

____ Install the red lead as shown coming from the +12 standoff and Pin 4 as shown.

You will build the 12V and bias control with this picture. Circuit below:

Using the circuit diagram and the picture, place the following components:
____ 1 - 22 mfd electrolytic capacitor, 50 volt
____ 1 - .22 mfd capacitor
One lead of the 22 mfd capacitor will be soldered to ground and the other lead as a tie point for the center lead (out) of the LM317T.
One lead of the .22 mfd capacitor will be soldered to ground and the other lead as a tie point of the right hand lead (In) of the LM317T.

____ 1 - 1.5K resister - one lead will be soldered to ground the other lead to the "prm" connection of the LM317T
____ 1 - 240 ohm resistor - will be soldered between the "prm" and "out" of the LM317T
____ 2 - 2N3904 transistors - Looking at the flat side of the transistor, the leads are E, B, C left to right. Each transistor is soldered to the ground plane with the E pin. See picture for location and orientation of the transistor. Notice which way the flat side is facing.

____ When soldering the emitters to ground, bend the bottom of the lead at a 90 degree angle and solder to the ground. Makes for a good solid connection.

____ The first transistor has the base lead bent to the back side (curved) and the collector lead bent forward (flat). After the emitter is soldered to ground (note flat side orientation), solder the collector to the top of the 1.5K resistor.

____ The 2.2K resistor is soldered to the collector lead of the transistor and to the "IN" on the LM317T and the .22 capacitor junction. This junction will be left floating with no ground support.

____ The second transistor has the emitter lead grounded just like the first transistor.

____ The base lead is pulled forward (flat side) and the collector is pulled backwards (round side). After the emitter lead has been soldered to ground, solder the collector lead to the base of the first transistor that has a 2.2K resistor soldered to it.

____ The base lead will be floating alone. Take a 2.2K resistor and solder one end to ground below the base lead, then solder the top lead of the resistor to the base lead of the transistor.

____ As shown in the picture, there is a 1N4006 diode in which the anode is soldered to ground, the band of the diode, the cathode, will be at the top of the diode. Leave enough room between the second transistor and the diode to solder a resistor.

____ The resistor is a 6.8K and is soldered between the base of the transistor (with a 2.2K soldered to the lead) and the 1N4006 diode, cathode side (which should be on top with a band on the upper end).

This makes the voltage to power the relay connecting either the 6 Meter antenna or the receiver antenna.

The picture above shows how to connect the 6 Meter antenna and the receiver antenna with a relay that will do the switching.
The parts are the following:
____ 1 - DPDT small relay, or similar
____ 1 - Connector to connect to the 6 Meter antenna, I used a solderable Phono connector but a coax connector could be used if a back panel is installed.
____ 1 - An 8 inch or so cable to connect to the receiver antenna input.

As shown in the picture, the 12 volt transmit switch voltage is taken from the top of the 1N4006 diode in the bias and switching circuitry.

____ The connector for the 6 Meter antenna is mounted along with the relay.
____ The 12T power from the 1N4006 diode is connected to one end of the coil of the relay. The other coil connection is connected to ground.
____ The common connection(s) of the relay is connected to the 6 Meter antenna connection.
____ The NC (normally connected) connection(s) is connected to the receiver cable.
____ The NO (normally open) connection(s) is connected to the transmitter output.

Shown above is a 2N5109 broadband amplifier from KitsandParts.com

This amplifier brings the signal level from the output of the VFO to the level that is perfect for driving the 6 Meter amplifier. It is very stable and room for a 50 ohm 3dB output pad to enhance stability. One is shown in the schematic shown above. At this time, it is still available.

If you can't find one, it can be built dead bug style very easily. The one used at the input of the BLT receiver would work great with the 3 dB pad at the output as shown in the receiver. You would need one 18 ohm and 2-300 ohm resistors for the pad.

Power with 13.8 Volts

The diodes are RU42s, two amp rating. This drops the 13.8 volts to a little below 12 Volts.