Monday, 13 August 2018

Adding 60m to the SBX-11

As I had an unused channel position and spare set of red coils for the SBX-11which cover the frequency range 4.00 to 5.66 MHz , I decided to add crystals for the 5.400 MHz 60m spot frequency to allow operation on the 60M band .

Calculation for the crystals for the SBX-11 is as follows -

  • Determine the centre frequency of the of the channel - 5.400 MHz
  • Subtract 1.5 KHz from the centre frequency to get the supressed carrier fequency . 
  •  5.400 MKz - 1.5 KHz = 5.3985 MHz  
  • Add 456.5 KHz to the suppressed carrier frequency
  • 5.3985 MHz   + 0.4565 MHz = 5.855 MHz 

The SBX-11 uses 2 x HC-6/U crystals which are difficult to find, so I ordered some smaller HC-49/U crystals from in the Czech Republic  using the following spec -

Frequency         5.855 MHz / fund.
CL:                    32 pF
Package:            HC-49/U
Adjustment:      ± 15 ppm at 25C
Stability:           ± 30 ppm in OTR -30/+50 CC

cost for two crystals , VAT and shipping came in at about €26 and the crystals arrived about 2 weeks later .

Rather than solder the smaller HC-49/U crystals in to the SBX-11 I decided to use some old HC-6/U crystals to make adapters.  Using a hot air gun it was possible to desolder the case on a HC-6/U crystal , remove the old quartz crystal and solder the HC-49/U in its place .

The old casing was then soldered back over the new crystal .

SBX-11 crystal slots showing red coils in place and empty crystal positions
Orange coils - 5.66 to 8.00 MHz are used with an 40M crystal
Brown coils - 2.82 to 4.00 MHz are used with an 80M crystal
White coils - 1.6 to 2.00 MHz are used with a 160M crystal

 new HC-49/U crystals in HC-6/U cases in place
Crystal cover in place

The new crystals were adjusted for correct frequency using the crystal trimmers while measuring the frequency at the Tx HFO and Rx HFO test points using a frequency counter connected via a 10pF capacitor .  Alignment carried out as per section VI of the SBX-11 service manual 

Update the label with the new channel frequency .

Initial on-air testing indicates that I am getting out > 6w and the receiver is sensitive .
more testing to follow .