Friday 5 September 2008

Setting your radio for weak signal work

At VE3MPG digital modes are the preferred operating mode. I use low power and stealth type antennas and have been using PSK modes since I acquired my FT-100 in 2000. I ran across a really great article written by Larry, W7IUV, where he explains how to set up a FT2000 (or the FT-950 or any rig for that matter) for weak signal work and I'll quote some of his superb information below:

One of the biggest problems I see is that most people either don't know how to set up a radio for weak signal or they do and refuse to do it due to some personal agenda. Here's the way to hear weak signals either SSB, or CW;

Listen to the background noise. Does it move the S-meter at all? If yes you have the radio set up wrong. Yaesu provided a switch to select preamps or not and another switch to select input attenuation. USE THEM! On the low bands (160-30 meters) I will almost never operate with one of the preamps on. IPO ON all the time. Look at the S-meter. If it wiggles at all with background noise, add attenuation until it stops wiggling. On all modern radios there is about a 20-30dB difference between MDS and where the AGC starts working. You want the background noise (QRN, power line, QRM, whatever) to be at a level just below the point where the AGC starts working. That's also the point where the S-meter starts wiggling! At this level, when you tune across a weak signal it will jump up out of the noise at you. Note that setting the radio this way will NOT impair your ability to hear the weakest signal possible with current band conditions. The S-meter does not tell you S/N, stop trying to make it read upscale all the time!

Use the narrowest filter possible. Wide for me is 300 Hz. That's what I use for trolling the band. When things get tuff, I switch down as far as possible. Learn to use the narrow filters, they work far far better than screwing around with the shift and notch and other do-dads.

Do not use the RF gain control. If you have a SX-100 or a HQ-180 or maybe a R-390A it's a good thing. With modern radios like the FT-2000, using the IPO and ATT is far more effective. Also, depending on how and where the AGC voltage is applied to the RF and IF stages, using the RF gain control could possibly reduce your IMD performance and reduce you ability to hear weak signals due to increasing the noise figure faster than reducing the gain.
I've tried Larry's methods and on my 'old' FT100 it works great. On the FT-950 it works even better. I can copy weak psk signals better and it gets rid of much of the background noise. The signal traces on digital modes become very distinct using this method.

More info on Larry:

Larry - W7IUV

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