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 Krystaly.cz in the Czech Republic using the following spec -
Frequency 5.855 MHz / fund.
CL: 32 pF
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
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 .