> If memory serves, K9YC has curves for both the Bournes and the Triad.
If Jim doesn't, Jack Smith K8OZA has them on his web site.
> The inexpensive one is the Bourns LM-NP-1001-B1L,
I believe Elecraft have a version of the Line Out board that uses the
Bourns transformers - at least there is reference to them in the latest
K3 schematic package, I would also be remiss in not pointing out that
microHAM have been using the Bourns LM-NP-1001 exclusively for the
last five plus years.
73,
... Joe, W4TV
On 4/4/2012 12:49 PM, Kok Chen wrote:
> To reenforce what Bill said, for quite a while now, K9YC has been advocating
> the bonding of chassis. This white paper is as good a place as anything to
> understand the problems of interfacing to a radio:
>
> http://audiosystemsgroup.com/RFI-Ham.pdf
>
> Jim has posted very often to the Elecraft reflector about this, but for some
> reason, it keeps falling on deaf ears (as is the Pin-1 problem with
> commercial interface boxes).
>
> The biggest advantage of what Bill (and Jim) mentioned is the fact that a
> transformer adds IM distortion. It is much better, and cheaper to boot, not
> to even include them in your audio chain. IMD is not a problem if you use
> receive filters that only lets through a single signal, but can be
> detrimental when you open up the passband to multiple signals (for the same
> reason that you use 24 bit sound cards with wide passbands). IMD can also be
> detrimental to modes like PSK31 under single signal condition, but in
> practice, the transmitters themselves are dirtier than mediocre transformers.
>
> If you really must make do with transformers, K9YC's web site also has white
> papers about transformers and Jim has many measurements.
>
> I had already passed along to Don last night a decent $2 transformer (you
> need 3 transformers of course for a transceiver that has 2 receive outputs
> and one AFSK input), together with a slight better but much mode expensive
> one.
>
> The inexpensive one is the Bourns LM-NP-1001-B1L, which you can pick up from
> places like Mouser. I have for example replaced the transformers in my K3
> with the Bourns.
>
> If you want to splurge, I feel that the Triad SP-70 is a bit better, but will
> cost you nearly $50 for a set of three. You can also get the Triad from
> places like Mouser and Digikey (heck, 90% of you who build your own stuff
> probably already have accounts with them :-). Incidentally, the Triad SP-70
> (might be the SP-71) is the transformer that are used in Larry N8LP's LP-PAN.
>
> If memory serves, K9YC has curves for both the Bournes and the Triad.
>
> One other trick that Bill did not mention is the use of balanced audio. Many
> halfway decent sound cards come with balanced TRS inputs (the ST-8000 also
> uses balanced TRS, by the way -- this is not a new thing among hams, perhaps
> just forgotten).
>
> You can actually see a picture of this technique used here (with an E-MU
> sound card) when I measured the IMD from my K3.
>
> http://www.w7ay.net/site/Technical/K3/Content/imd.html
>
> A short description appears on the second paragraph below the picture. The
> actual audio cable was some junk twisted pair CAT-5 UTP that I had hanging
> around which I soldered to the 1/4" TRS plug.
>
> Speaking of which, K9YC also advocates the use of twisted pair cables for
> audio connections. If you have time, go visit Jim's web site. You can have a
> fun afternoon with various topics, from RFI to Audio to "Pin 1."
>
> 73
> Chen, W7AY
>
>
>
>
>
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