[WriteLog] Audio Situation & RF

Bob Naumann - W5OV W5OV at W5OV.com
Tue Nov 22 00:56:38 EST 2005


I have used several different sound cards in various brands of computers,
with excellent results.  The performance is as good as it used to be with a
K1EA DVP.  No noise.  The notebook computer I use is an IBM 600E ThinkPad.
I plug the Heil right into the audio in jack on the laptop, and the audio
output right into the SO2R switch box.  Mine is homebrew, but does the same
as your DXDoubler (DXD).

Your "tech pal" was wrong when he assumed that connecting all the mic
grounds together would be OK.  Some radio mic input "grounds" (mic low side)
are not really grounded, and if you do ground them, it may cause problems.
Kenwoods are especially susceptible to this.  This may be what you have

I'm confused why you are rigging up additional relays when the DX Doubler's
purpose is to handle all of the SO2R switching for you - including
footswitch, mic, headphones, key, etc.  I also think your focus on using VOX
is somewhat misguided.  When you use PTT from the computer to send the WAV
files, the computer handles the PTT so the radio will transmit only when it
is supposed to.

What purpose does the signal link box serve?  I don't think you need this

What is the purpose of all the mono/stereo adapters you are struggling with?

WriteLog, in tandem with the DX Doubler, should do everything you want/need
to do SO2R without any of the hassle you seem to be having.  Page 12 of the
DX Doubler User's Manual shows the diagram of everything you need.  The
diagram shows a DVP, but in your case, that is equivalent to the computer
sound card's input and output.


Bob W5OV 

-----Original Message-----
From: K6VVA [mailto:dx35 at hilding.com] 
Sent: Monday, November 21, 2005 4:16 PM
To: writelog at contesting.com
Subject: Re: [WriteLog] Audio Situation & RF


TNX again for the multitude of direct emails and several posts of ideas.
I'm posting a more detailed explanation here as I suspect more than one
person out there may be wrestling with some of this, or will be, but perhaps
a bit shy about asking for help.

SS is now over.  I finally got on at 0125 Zulu (about 4.5 hours after the
start)...no DVK /SSB message capabilities this year...only a mic (like the
"Good Old Days").  Umh, I really never want to have to "manually" call "CQ
Contest" again in my life !!!

I do believe a minor tweak to future version of WL would give anyone in need
more "flexibility" for handling audio routing to fit any *specific* setup
needs.  A simple config option based upon Microsoft's "Where Do You Want To
Go Today" (or something like that) could eliminate some potential
headaches...especially in dealing with what I will term FLAKY Stereo 2 Mono
audio adaptors.

Config Example:

1. ___ Let WL switch audio L-R by default

2. ___ Combine L & R audio into "TRUE" Mono

3. ___ etc., etc.

This would have made life much, much easier.  After 5 trips to Radio Shack
on Friday, Saturday Morning & Saturday Afternoon (DURING SS), I think I have
enough stuff cables and adaptors hee to almost open my own store.  None of
the alleged "Stereo To Mono" cables or adaptors worked. 
IMHO, there should be a law against labeling anything as a Stereo 2 Mono
adaptor that doesn't do just that...combine the L & R sources into a "Mono" 
output ;-(

Some folks said just tie the L & R wires together, whereas another person
said that could potentially damage/short out my Notebook audio card.  Talk
about indecisiveness here for a few hours!!!  I finally bit the bullet
Saturday Morning & cut a Stereo Cable in two and wrapped the L-R wires
together and *THAT* part worked.  I tried going directly from the Notebook
computer audio out into the DXD (that worked...dunno why I never thought of
it before...TNX!), but unfortunately, plugging the Heil into the soundcard
"Mic In" doesn't work.  Well, it does, separately, but you have to click the
"Record" button (I've recorded that way before outside of WL).  I tried
every setting I could find but simply "No Joy".  My thoughts are that going
this route, even if it worked, will add more unnecessary noise into the mic
line.  SignaLink recommends turning off any soundcard options other than
what's needed to get the .wav file audio out due to the VOX sensitivity

For portable & Expedition purposes, the SignaLink still remains a good
choice for use with a Notebook computer because they are extremely small,
lightweight, and carrying a 2nd unit as a safety backup...I can slip it
inside a jacket pocket.  So yes, things are a bit more "complicated" here
due to fixed AND portable operation needs.

The original purpose of the external VOX operated audio card(s) was prior-to
SO2R plans. I checked into a Rigblaster at HRO on Friday, but they didn't
have the PRO version and in any event I'm max'd out on IRQ's for another USB
to Serial interface since I'm already using several for rig control from the
Notebook (this makes things more challenging vs. 
Standalone computers).

Had the SignaLink folks not been short on parts to modify my 2nd unit, due
to the way WL handles the audio ("Non-Negotiable"), I would have still had
the problem.  My bad for not getting at least the one unit back from them
until two days before SS ;-)

Saturday Morning, I went to my tech-buddy's place with a box full of Radio
Shack parts, and we built a little "Black Box" with a 12vdc relay to switch
the audio/mic lines from L-R radios with a Heil Footswich.  The plan was to
have the mic & .wav file audio switched by the normal Amp-keyline coming out
of the f/switch, and the DXD PTT activated by the 2nd f/switch line which is
triggered last.  The box connections are:

* SignaLink audio in (handles the Notebook computer audio out) - Relay
normal routes to DXD audio In
* Heil HC-4 mike input - Relay engergized routes mic to DXD audio In
* Ouput line to DXD Input
* F/Switch line to activate relay
* 12vdc line input

We finished about 1/2 hour before SS, and I rushed home, hooked everything
up about 1 minute before the Checkered Flag dropped.  The .wav file audio
worked AOK switching between L & R in WL via the DXD Auto operation.  Then I
pushed the footswitch and started to speak.  UGH!!!  Bad News audio from the
mike...even ramping down to only 5watts output...most likely some kind of RF
problem in spite of the all metal black box (it is really black :-)

So back into town again where my tech pal put some little capacitors across
each connector jack on the box, which was *supposed* to fix the RF problem.
I rushed back home, only to find *** NOT *** ... there was still real bad
sounding mic audio.  So it was off to Radio Shack again for several handfuls
RF chokes, which I stuck on every cable.  Still No Joy.

In all of this, the old adage "Every Problem Is An Opportunity" has proven
to have some merit.  Using only one SignaLink via the DXD (tnx to many for
the suggestion) will, in fact, work.  This morning, my tech pal suggested
unplugging the 12vdc line, and putting the Heil mic line into the normally
static-position input via the Black Box relay (so the Mic connection would
be routed to the DXD without needing to activate the relay).  *** BINGO ***
that works OK...at least at 5w, although IMHO, the rather lengthy wire leads
*inside* the black box from the connectors to the relay still seem like this
wouldn't be too RF Friendly.  But then again, I am not a tech person.

The relay is only switching the center lead of the audio lines, as my tech
pal said the connectors/ground side all share a common ground via the
connector mountings in the metal box.  So, the monster $64,000 question that
remains, is how on earth to get rid of what appears to be an RF problem
gumming up the works?  He suggested I may have to use a shielded 12vdc line.
Should shielded lines be used *** INSIDE *** the box from the connectors to
the relay contacts?  I believe the Red RCA tipped line from the f/switch is
shielded cable.

"Isolation Transformers" have been suggested by several (including the NA7XX
guys on the 3830 post-Net chatter session last night), but I claim
cluelessness here.  If, in fact, these are a necessary part of the solution,
I would appreciate any assistance.

My apologies for the lengthy post, but I sincerely hope there may be others
who can benefit from the info *** BEFORE *** they travel down the same road
of headaches.  Especially those with dual fixed & portable/Expedition
station needs.

Sincere TNX & 73...

Rick, K6VVA

WriteLog mailing list
WriteLog at contesting.com
WriteLog on the web:  http://www.writelog.com/

More information about the WriteLog mailing list