Caution: This is quite involved. If you are not too good you might be advised to get someone who has the experience to handle this mod! This mod requires the service manual, a propane torch for desoldering the SMDs, and desoldering braid for cleanup.
The two VHF Rx filters are on the PA unit, between the EXT SP jack and L29 L30 (two tunable metal boxes). The wide filter is used if the B8W signal is active ([60--144[ and [148--200] range).
L29 and L30 form the 144-148 band pass filter, with a 2 dB loss.
The wide filter works from 60--120 MHz, see plotrxold.pdf. Since transmitting below 120MHz is impossible due to spurious emission at ftx+70MHz, I decided to modify the rx filter for a 110--180 MHz operation.
Note that the low pass VHF input filter has a -7dB roll-off at 160 MHz.
New component values:
C57 1nF L26 150nH L40 39nH
C56 47pF L25 120nH L49 33nH
C55 18pF C52 0pF C51 1nF
C54 32.6pF (27+5.6) C53 15pF C153 12pF
C151 15pF C152 15pF C154 1.8pF
Caps in 0603 size, Farnell or Johanson. Inductors in 1008CS size, Coilcraft.
Results are in plotrxnew.pdf and p_nf.pdf.
Noise figure data.
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