K0HB's spectrum analyzer measurement (attached below) is in fact consistent
with previous measurements. Unfortunately, he reports the spur magnitude at
only one split: 3khz. At the smaller splits typical of CW pileups, the spur
becomes much larger.
The following measurements were taken on 12m from two different 0-district
775s:
SPLIT SPUR (relative to main signal)
10 kHz -55 dB
6 kHz -50 dB
3.5 kHz -45 dB
2 kHz -40 dB
1 kHz -35 dB
800 Hz -30 dB
At -30db, a 1.5KW main signal means a 1.5W spur. Icom's spurious emission
spec for the 775 is < -60db.
As to relevance, keep in mind that Icom's improved shielding corrects the
problem on the lower bands. From the 775's perspective, 10m and 12m CW
pileups are a recent phenomenon. As cycle 23 progresses and these bands open
more frequently, the incidence will increase. And with the low D-layer
absorption typical of these bands, 1.5W of QRM on the DX frequency will
cause plenty of trouble.
As to workarounds, I certainly know how to use XIT instead of split. Before
sending my 775DSP back to Icom for "study", that's been my modus operandi on
12m and 10m since discovering the problem. Not even Icom has suggested this
as a reasonable long-term solution.
As to motivation, I have exactly one objective: convince Icom to correct the
775 design error, and retrofit the correction into units in the field. To
that end, I have spent far more time jawboning Icom management over the past
5 months than the 775's replacement cost would justify; I generally like
Icom's products, and believe that its in their best business interest to
prioritize customer satisfaction over new product development. But prospects
for the success of this approach are waning -- hence my public response to
9K2HN's question. Sadly, it appears that nothing short of economic impact
will convince Icom to stand behind its products. The internet will certainly
accelerate this process.
73,
Dave, AA6YQ
> -----Original Message-----
> From: owner-icom@qth.net [mailto:owner-icom@qth.net]On Behalf Of K0HB -
> Hans
> Sent: Saturday, May 15, 1999 5:58 PM
> To: 'dx-list@makelist.com'; 'dx@qth.net'; 'icom@qth.net';
> 'fistlist@egroups.com'; 'cq-contest@contesting.com'
> Cc: 'dhb@mediaone.net'; 'jreid@alhoa.net'
> Subject: [Icom] IC775
>
>
> AA6YQ writes:
>
> > When operated in split mode with dual receive enabled, the
> > Icom 775DSP emits a spur on the receive frequency.
>
> ...clip...
>
> > Left uncorrected, the increasing Icom 775DSP population will
> > become a global menace to high-band CW DXing.
>
> For all his righteous indignation I give AA6YQ a D-minus for
> real-world relevance. Within a few miles of my shack are five
> users of the 775DSP. All are serious QRO contesters and
> DXers who are often all on the air at the same time in the same
> contests or chasing the same DX.
>
> None of us has noticed the "global menace" that Dave warns
> about.
>
> I agree that a spur exists, but my measurements at our cal-lab
> at work show it at >50db down with 3KHz of split. That figures
> out to 15milliwatts at full QRO (1.5KW). The FCC rules allow
> 50milliwatts, or over 3 times the worst case I have measured
> on two different 775DSPs. At 10KHz split the spur drops to
> >57db down.
>
> de Hans, K0HB
>
>
>
>
>
> --
> Submissions: icom@qth.net
>
--
CQ-Contest on WWW: http://www.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST@contesting.com
|