SIGNALINK USB Modifications
I have had numerous requests for
information regarding mods I have made to my Signalink USB, so decided it
might be appropriate to write a short article describing these mods, and
include a few pictures.
My present radio, an IC-7700, like many of the newer
radios, requires you operate your radio in RTTY Mode, in order to take
advantage of the special receiver filtering available for RTTY. When
operating in the RTTY mode, only direct “FSK keying” will work (AFSK
will not), and like so many other transceivers, the direct FSK keying line
is wired to the same accessory jack on the back of the radio that provides
the audio in/out connections for the digital modes, like PSK. When your
Signalink cable is plugged into the accessory jack, you cannot access the
FSK keying line L
To solve this problem, I mounted a 1/8” mini-phone
jack in the back panel of the Signalink USB. I wired the jack, thru a 2.2k
current limiting resistor, to a 4N32 opto-isolator. The output of the
4N32 is jumpered directly to the Signalink’s cable header, accessing the
FSK keying line, and ground leads, going to the radio. The 4N32 is mounted
to the inside back panel with a small piece of double-sided sticky tape.
For RTTY operation, I prefer MMTTY and N1MM logger
software. MMTTY’s options, allows you to select direct FSK keying
via a Serial/Com port TxD lead, so all you need to do is extend the TxD lead
and ground from your computer to a 1/8” mini-phone plug, and plug it into
the back of the Signalink. Now, you can simply change between PSK and RTTY
I have included three pictures below that describe
this simple mod.
Signalink Performance Improvements
While attempting to use our Signalink USB’s for
remote access using Skype, several friends and I discovered there was
audible tones, and trash in the noise floor. Upon searching the web
for an explanation, we discovered Peter-OZ1PIF’s article describing
several mods that improve it’s performance.
Here’s a link to Peter’s Web page describing his
research and mods for the Signalink USB::
I wish to thank Peter OZ1PIF for all of his wonderful
For those of us in the USA, interested in making
Peter’s mods, I will provide a Mouser Parts List at the end of this
write-up.. The improvement in lowering the noise floor and frequency
response is well worth performing these mods.
Since I did not have a small inductor to place in
series with the 5V USB power, I chose to just bypass the 5V supply line with
a 100uf tantalum cap, which seems to work well. A small inductor could
easily be constructed by winding several turns around a ferrite bead or
small toroid core.
The audio matching transformers I used (ETAL
P-3356) were provided by a friend who purchased it from Farnell.
Same may be purchased for GBP
2.30 from Farnell. As an alternative, I am providing the part number for
the Triad xfmr that Ed, K6ED used when performing his mods. Bend the
transformer leads to match the pads on the pc board, and tilt the
transformer, so you can solder the inside leads, then bend it down and
solder the leads closest to the edge of the PC board. Any good quality
transformer should do the job. The Signalink pc board is stenciled showing
the primary winding side. Make sure you install the transformers in
the proper direction.
The three 220pf disc ceramic caps are used to bypass
the USB lines coming from your PC. They are located on the bottom of
the PC board. Peter used SMT components, but I am “OLD” and found
the disc ceramic caps easier to work with J
2 600 ohm Matching Xfmr
4.7uf 10V Tantalum Cap $0.34
33uf 10V Tantalum Cap $0.73
100uf 10V Tantalum Cap $2.75
3 220pf disc ceramic Cap
I have included a couple of pictures showing the yellow
tantalum capacitors, and transformers I used.
Good Luck, and I am sure you will be happy with the
improved performance of your Signalink.
Thanks Again Peter.
73’s Frank, K7SFN