Error issue see Errata. You need to correct item 1

PCB must have the following modifications carried out during assembly:

• it is recommended that a diplexer is used after the VHF BPF
• If using S18 inductors, prepare shielding for both of the VHF BPF's - for L205/206, use a piece of hobby brass 67mm x 17mm. Fold each end in at 17.5mm. Cut a screen to fit centrally between the two coils. For L601/602, the procedure is identical - but the screen is 61mm long before bending.
• There is no position marked on the PCB for C504A or C505. C505 should be places between the 'hot' end of L502 and a ground point. C504A should be placed in the original position of C504

The 106.5MHz version requires:

• the diode multiplier (Sheet 2),
• Logic Stages with 2 dividers (IC402/403) - both inverter packages (IC401/404) required (Sheet 4)
• 5MHz low pass filter, (Sheet 9)
• 0.5MHz low pass filter (sheet 3)
• 5.5MHz BPF and tripler to 16.5MHz (Sheet 5)
• 106.5MHz BPF/diplexer, amplifiers, crystal filter and output LPF (Sheets 6 & 7)

The input buffer circuit (Sheet 1) can be used to provide a 'daisy-chain' 10MHz output with this implementation.

The Input Buffer input attenuator (Atten 1) should be set for 7dB if the drive level available is +10dBm - Adjust the value according to your input signal to obtain +10dBm at the input to the diode multiplier.

Set the attenuator following the VHF multiplier chain to give around 0dBm into the mixer RF port - often 3dB is the correct value here.

The attenuator following SJ902 (if required) should be set to give a level of approx +6dBm into the mixer LO port.

Divider 1 (IC402) must be set to divide by 2 to give 5MHz output - hence the jumpers must be programmed as binary 14 (1110) reading in order DCBA. Jumper A (pin 3, SJ1) must be grounded, the remaining 3 taken to the 10k pull-up resistor, R403

Divider 2 (IC403) must be programmed to divide by 10, requiring 6 to be set in binary - 0110 - this gives the 0.5MHz output from the 5MHz. Jumpers D and A (pins 3 and 6 - SJ9,12) must be grounded, the other two going to the pull up resistors

Divider Outputs: Divider 1 output is taken from pin 14 (SJ5). Divider 2 output (IC403) is taken from pin 12 (SJ15).

Standard ADE-1 mixer required for M601, ADE-6 mixer for M501

Tune each filter onto frequency using a signal generator and power meter or spectrum analyser as you go through the construction. This will ease the final tune up. As you complete each chain, adjust it before the mixer is inserted.

For example, build the 90MHz filter, align it, then build the amplifier stages following. Check and re-align. Build the diode multiplier and test through to output of the amplifiers. Set the attenuator value to give approx +6dBm into the mixer. Build the logic stages and check the output is correct in frequency. Using a scope, check that there is a nice square wave output from IC401, pin 2 (may be easier to look at IC402 pin2) Check output of divider through LPF - you should see approx +12dBm (>7vp-p) of 5MHz present, and approx +6.5dBm (5vp-p) of 0.5MHz. The 5MHz signal needs a 6dB attenuator before the mixer. No attenuator is needed on the 0.5MHz signal.

Build the 106.5MHz BPF/diplexer and align it - the series path is set for max 106.5MHz signal, and the shunt path is set for minimum 73.5MHz. Once both the 90MHz and 16.5MHz outputs are optimised, insert the mixer and check the output through the diplexer and BPF, optimising if necessary. Follow through with the remaining filters.

Final alignment should be done on a spectrum analyser. Carefully adjust the trimmer capacitors of the crystal filter for minimum spurii, and maximum wanted signal. The adjustments are iterative, and very small movements make significant differences to the output. You may also find it beneficial to make minor adjustments to the 90MHz filter and the 16.5MHz filter to get the best rejection of other products.

Typical results are Wanted output: +8 dBm (+5dBm with diplexer)

Spurii < -70 dBc

Harmonics < -40 dBc

Supply voltage - 13.8V DC

Current drawn - 410 mA

Completed 106.5MHz DFS - topside view	Output Spectrum 0 - 500MHz. Top of scale is +10dBm	Output Spectrum +/-25MHz. Top of scale is +10dBm
Output from my DB6NT 3cm transverter driven by DFS 106.5

Because this DFS implementation uses widely spaced LO and RF signals at the VHF mixer (M601) it is advantageous to provide a diplexer, to correctly terminate the unwanted products from the mixing process - the image output, and the LO feedthrough. This reduces the levels of spurious components present in the final stages of the DFS circuitry, and also helps to keep the following LO multiplier chain cleaner. On this specific example, addition of the diplexer reduced the close in spurious components around the 10GHz Tx output signal by a further 10-12dB. It is worth noting that no great difference was seen on the 106.5MHz spectrum, since the spurii are already at or below the spectrum analyser noise floor.

Page created 19 May 2008

Page last updated 7 JUn 2009