[RFI] Fwd: Re: DigiKeyer II

Jim Brown jim at audiosystemsgroup.com
Wed Dec 18 02:13:25 EST 2013

Thanks Joe. I'm forwarding to the RFI list .

73, Jim K9YC

-------- Original Message --------
Subject: 	Re: [RFI] DigiKeyer II
Date: 	Tue, 17 Dec 2013 22:30:44 -0500
From: 	Joe Subich, W4TV <w4tv at subich.com>
To: 	jim at audiosystemsgroup.com


Since I am not a member of the RFI list (I do enough others <G>) I'll
just respond to you.

Digikeyer II is a *digital/CW mode interface only* - it is not specified
for voice operation.  This user has been told that and he refuses to be
limited by the published specifications.

The audio connection (for AFSK, PSK31, etc.) to the Icom transceiver
is via the ACC jack "modulator input" - there is no bypassing or
filtering on that input in the transceiver.  The Icom 746 and other
Icom transceivers of that era were extremely sensitive to common mode
RF (on the feedline) when that input was used - particularly since the
transceiver made *no provision* to mute the microphone!

There is not likely to be a "power supply ground loop" issue since the
interface is powered *from the transceiver* via the +13.8V pin on the
ACC jack *unless* the user has a defective transceiver power cable and
bonds the case of the interface and the power supply together (tie
power supply return to case and ground power supply case).  In that case
he could force transmit return currents through the interface creating
the very problem we try to avoid by powering the interface from the

I would suspect common mode issues - either RF or DC due to a bad power
supply return (note there no problem with DC common mode in PSK31/AFSK
operation since both are essentially constant current modes!) - but
since the product is *intentionally* being used contrary to its
specifications, I will not support this user.


   ... Joe, W4TV

On 12/17/2013 9:50 PM, Jim Brown wrote:
> Hi Peter,
> See comments interspersed.
> First, download and study k9yc.com/RFI-Ham.pdf  I suspect a Pin One
> Problem (see the tutorial) on the 746.
> On 12/15/2013 2:15 PM, Peter Laws wrote:
>> IC746Pro, microHAM Digi Keyer II.
>> One USB cable from the radio to the interface.  One squid from the
>> interface to the radio with 1/4" plug for CW, a 1/8" plug for CI-V and
>> a howevermanypin DIN for ACC1.  There are snap-on chokes on the ACC1
>> cable and the USB cable from the factory.  The interface is connected
>> to the ground bus and the bus is connected to a ground rod buried
>> outside the window.
> A connection to earth is NOT part of a solution to RFI.  Proper bonding
> of equipment IS.  That includes short fat copper (#10, or copper braid
> stripped from transmitting coax) from every chassis to every other
> chassis that is interconnected. In your case, that means from the
> computer to the microHAM to the 746. The rig must also be bonded to the
> power system ground, and to all other grounds in your home.
>>   Radio is also connected.  To make sure
>> (hopefully) there was nothing coming down the coax, there is one of
>> those Palomar buildityourself chokes on a foot long piece of LMR400 in
>> the shack.
> Useless.  See the tutorial. Also see the Power Point on Coax Chokes at
> k9yc.com/publish.htm Those cores are resonant around 2M.  For a choke to
> be effective at HF, we must move the resonance down to HF by winding
> multiple turns.  Again, study the tutorial.
>> Interface works OK and I played a little in CQ WW RTTY and November
>> Sweeps CW.  I use FSK not AFSK so that's hard keyed as is the CW (I
>> think I set it to use the internal K1EL chip).  All of that works
>> great.
>> But when I went to play in SS SSB, I had horrible horrible RF getting
>> into my audio.
> Maybe a Pin One Problem, but also a possible power problem.  How are you
> powering your microHAM?  The wall wart that came with it, or from the
> 12V bus?  Use the wall wart, not 12V.
>> I finally had time today to troubleshoot.  SWR (on three wire antennas
>> coming through an Ameritron remote switch) was acceptable but best on
>> the WARC band trap dipole (in fact, I'd forgotten just how well that
>> antenna works even without the tuner.
> SWR has nothing to do with it.
>>   I went to 17 where I knew the
>> SWR was good and did some tests. I can hear the distortion through the
>> headphones with the monitor on.  Unplugged CI-V, no change.  CW, no
>> change.  Unplugged ACC1 .... no more distortion.  Got on 17 and
>> chatted with a feller up in Indiana and he heard no distortion either
>> (though I gather the HC4 in my Heil boomset wasn't doing me any
>> fidelity favors :)).  Plug ACC1 back in, back to interference.
>   Is this problem present on all bands, or only on 17M?  Take one of
> your ferrite cores and wind 4-5 turns of the ACC1 cable through it. Do
> the same with the USB cable.
>> Interestingly, this unit doesn't power itself off the 5 V available on
>> the USB connection but off the 8 V available off the ACC1.
>> I've added two more snap-ons of unknown mix to the big cable from the
>> interface and this has made no difference.
> Again, ferrites do nothing at HF unless you wind turns.
> I also suggest that you contact Joe, W4TV, who makes it his business to
> know the common cause of issues with his products.  I doubt that the
> problem is in his gear -- I think he got them fixed years ago.
> 73, Jim K9YC

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