TopBand: Follow-up on Topband Receiver Survey

[Robert A. Kile]

>    One comment on the survey: on 160 m receivers, selectivity plays major
>role, especially in the contests. I have found that at the times 125 Hz
filter
>cuts the band noise down, improving S/N ratio. This in combination with DSP
>filtering makes some signals "come out" of noise. Installing better filters
is
>the single most important modification one can make on any radio. The old
930
>with sharp filters can come close or beat much more expensive radios with
>"stock" filters.

Mixers 1st, Low Phase noise 2nd, premium filters 3rd, features 4th

>(Knowitalls at Kenwood refuse any cooperation with us "racing drivers")
>de Yuri, K3BU, VE3BMV

Top banders

The filters used today are the same as in the TS-930. The catch is the
really good filters were in the second selective IF (455) Some of the newer
rigs are again double conversion using the not so good filters at or near
9Mhz for primary selectivity. This is true in all cases (ICOM, KENWOOD and
YAESU)  If the factories would offer 500 Hz, 400 Hz, 250 Hz, or 125 Hz
filters with 8 poles and shape factors of 2.5 to 1 the little inexpensive
rigs such as TS570 and FT-920 would then be very comparable to their triple
conversion High Priced counterparts in selectivity. In many cases I might
add they already exceed the their high priced brothers is IMD.

Hams have had little influence on the equipment manufacturers in this
industry regarding specifications. The specs for the most part read the same
today in the brochures as they did back in the early 80's. Unlike the audio
industry where diehards have given true meaning to specifications, ham
equipment remains generic. Example: audio power > 1.5 W @ <10% distortion.
We hams are partly to blame. We buy the stuff. Further, we let QST and their
respected technical reviews sluff off performance specifications in fine
print with subjective and suggestive comments such as "Really easy to
operate". There is no reason why a 1997 transceiver should get a stamp of
approval with transmitter 3rd order distortion comparable to SWAN 350's of
the late 60's!!!!! I don't think I would want one as a neighbor running high
power.....


Sincerely,

Bob Kile, KG7D
www.hrshowcase.com



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