Saturday, 28 February 2015

Improving the FT-1000mp Mark V RX

I have been on a mission to make the most of the equipment in my shack, I didn't want to get sucked into buying more radios or very expensive new models to chase a very small improvement. I decided the next best thing was to squeeze every improvement I could out of my existing equipment.

I have been really pleased with the RX on the FT-1000MP Mark V and wanted to get all of the filters loaded into it. It has taken me some time but I have finally tracked down the full set of Yaesu filters to install in the radio and improve the way the RX performs when using narrow filters. I have already done the NB mod that is documented earlier on my blog. I have now managed to add the 2.0kHz SSB 500Hz and 250Hz in both the 8.2MHz IF and the 455Kz IF. I can assure you that having two 250Hz filters inline can really help improve the signal to noise for CW and for RTTY/Digital modes. The 2.0kHz filters in line really help with SSB but it does make the signal less pleasing to the ear and requires some IF or carrier point shift to bring back the lower frequencies to audio.

This lead me to searching the internet looking for any other modifications that could help, I started to read about removing the Inrad roofing filter to improve the RX in the presence of close by big signals.  I started to dig a little deeper and discovered that some people attributed this to the distribution of gain in the IF stages. I then discovered an archived email thread that discussed a solution. The article I found can be seen here. there is a link to files on a blog that discuss the W2AJI mod to reduce the gain on the Inrad roofing filter board and prevent additional and unnecessary gain. Essentially it involves swapping out two resistors on the roofing filter board to make things better. R5 is changed from 12 ohms to 15 ohm and R6 is changed from 220 Ohms to 150 Ohms. (You can see the links in the original email reflector link above.) I do not have any test equipment in my shack to test the results but I do know that the performance appears to have improved to me and I was able to make some comparisons with and without the Filter board in line. All in all I seem to have been able to squeeze a little bit more performance out of the RX in the FT-1000MP Mark V and I like the results more than having spent £3500 + on  a new transceiver. All it cost me was some resistors, a little time and some good eBay finds for the additional filters.

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