HiQSDR-Modifications

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Modifications HIQSDR Transceiver

Important Modifications Board Layout V2.4t

  • Change Filter from L/C to R/C
Board layout: V2.4t
Date: August 2011
Problem:
Sensitivity at very low frequencies is bad due to high noise floor from 0..200kHz
Reason:
L5 and L6 in conjunction with the FETs in the attenuator tends to oscillate at low frequency
Solution:
replace the LC low pass filter L6 L5 to a resistive one. Change L5/L6 to resistors 10 Ohm 0805
and C62 C55 to 22µF 6,3V Ceramic 0805
  • Change the transistor of the antenna switch relay
Board layout: V2.4t
Date: August 2011
Problem:
Switching from and to Antenna 1/2 does not work reliable
Reason:
the trip voltage of the digital transistor BCR148W is slightly to high to switch.
Solution:
replace T4 BCR148W with a low voltage FET BSS138W
Position of the parts

  • Change adc gain resistor and rf choke for better adaption of TX working range
Board layout: V2.4t
Date: September 2013
Problem:
The standard working point of the tx level for most following modules (MPPA)
and optimum of clean signal is approx +10dBm output power of the MMIC.
Reason:
To set this +10dBm output power, a TX_LEVEL-value of around 40..50 is necessary in
quisk_config.py. This is in the very low possible range of 0..255 values and therefore
this results in uneccesary loss in TX_LEVEL resolution.
After changing R35 from 2K0 to 3K9, the +10dB TX_LEVEL is produced setting TX_LEVEL
to the midrange (around 120..130) of the possible 0..255 in range quisk_config.py.
Change also the value of L10 from 12uH to 2.2uH, this improves the working point to MMIC and
also improves the IMD3.
Measure:
Connect the TX output of the HiQSDR Board to an Spectrum analyzer or a RF power meter
and set TX frequency to 7.100 Mhz. Adjust the Quisk parameter tx_level to get +10dBm output.
To measure the IMD3 press the IMD button in Quisk and measure the IMD 3
The IMD3 at 10dBm output level should be better than 45dB, most HiQSDR has IMD3 around 48-50dB
after the modification. This results in an effective IMD3 of around 55..56dBc.

Position of the parts

Position of the parts

IMD on 7.100Mhz with +10dBm tx level

IMD 3 before modification

Result after modification on 7.100Mhz with +10dBm tx level

IMD 3 after modification

Result after modification on 7.100Mhz with +10dBm tx level

IMD 3 after modification

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