[TAC] Icom 706 - using narrow cw filters on ssb for psk31

[mzedan at juno.com]

Hi Ian:
That software "trick" is very good.
The problem for future users is that some genious in the design section will think that this is a glitch, and order one of the writers to eliminate it from the code.


Mike, KN8Z
-- "Ian Hill" <ihk8mm at chartermi.net> wrote:
For those of you who are using an IC-706 on PSK31 and other AFSK digital
modes, here is a pretty cool trick to try. I tried it with my 706MKII and it
works great.


73,
Ian K8MM


There's some really great reasons to want to use PSK31 in a broadbanded way.
The problem is that there are some even more compelling reasons NOT to.
Like when that KW packet stations fires up 1kc away from your QSO and makes
your AGC go crazy. I defy you to copy clean PSK31 or anything else for that
matter.  The problem is that the current design for radios don't let us
effectively "notch" out one or more strong stations at the IF stage (most
notch filters are MUCH too narrow), therefore the AGC kicks in.  So, we cut
back the bandwidth, but it's getting to the point where even my 250 hertz
crystal filter isn't narrow enough to get rid of the inter-modal
interference.

Your rig wasn't designed to accommodate flexible digital modes. OK, you've
got several crystal filters, but does your rig let you click them in when
you're in SSB mode?  The answer for many users of older ICOM gear, and maybe
others, is "NO". So you put up with the problems mentioned in #1 above, and
try to find ways to work around the strong interfering stations. Or here's
another scenario that trips up even the newest of radios, such as the Icom
Pro and Pro II, and the Kenwood TS2000. You've got a desired PSK station at
an audio frequency of 1700 hz, and an interfering station at 1300 hz that's
500 hz wide. OK, so you try to bring up the low-cut DSP filter, but it
(incredibly) tops out at 1000 hz, leaving the interfering station intact and
strong as ever. You're stuck, and the only way to get this guy is to turn
the tuning knob on your rig (ackk!!!).

One possible fix (believe it or not) is that several of the rigs that lack
DSP are able to be lied-to, thus making them much more suitable for PSK31.
What you do is go into the appropriate menu, and tell them that that slick
300hz CW filter you installed is really a 1.9kHz SSB filter. THEN it will
let you select that narrow filter in sideband mode, and with any luck you
can slide the IF shift up or down to make it do its magic without having to
touch the tuning knob. Rigs that I've successfully fooled this way include
the Icom 706 (all current models), 746 (non-pro) and 756 (non-pro and
non-pro-II).

______________________________________________________________
TAC mailing list
Home: http://mailman.qth.net/mailman/listinfo/tac
Help: http://mailman.qth.net/mmmain.htm
Post: mailto:TAC at mailman.qth.net