[TenTec] Radio for soon to be newbie General....

[Joel R. Hallas]

Gene,

This is one of (and arguably the only "significant") difference between
the "mid-price" ($500-1000; Pegasus, Jupiter, IC-718...)  and
"competition grade" ($2K+, Omni VI, Onion..) radios. It has to do with
the "front-end" design and is expressed as dynamic range and
intermodulation distortion. The key is not just the noise problem, but
perhaps more importantly whether you can detect and/or receive a weak
signal next to a strong one.

Note that while the attenuator can help mask the symptoms by reducing
both wanted and unwanted signals, it won't help if you need the full
receiver gain and noise figure to copy just the weak signal. The RF gain
control is not quite as good as the attenuator, but has a similar
impact, it reduces both signals. (I say not as good because if the
signal reaches the input to the amplifier, it may cause the distortion
before the gain control can act on it. On the other hand, some "RF gain"
controls are actually variable attenuators and allow a bit more
flexibility than just 0 dB or 20 dB).

On 75M, the noise level is generally (but not always) so high that the
using the attenuator may help since the weak signal will be limited by
atmospheric rather than receiver noise, less true on higher bands. The
fact that an attenuator helps, by definition, means that the front-end
is non linear and that is what causes the IM distortion.

For most conditions we won't notice. On the other hand, sometimes we
don't notice because we don't hear that weak station at all and don't
know we have a problem!

Not sure it's worth $1-2K to me, but it is the BIG difference in radio
specs, and a hot item for the ad-men for the last decade or two. Perhaps
after the XYL let's me put up a tower and beam, it will become more
significant for me!

GL and 73, Joel Hallas W1ZR

Gene Buckle wrote:

> >    On the Jupiter you get a popping and static much like you do
> > with the noise blanker on the Corsair when it's set too high. Not
>
> Since I've never heard a Corsair, I'll take your word for it. :)
>
> > a problem though, turning on the 20db att. takes care of it.
> > About the  ONLY place that I have had a problem is on 75M at
> > night. If a signal is within the 20Khz passband and is at least
> > 25+ Db over S9 then I might get the problem on the station to
> > which I'm listening. However you can't tell the difference except
> > on the S meter when you turn the Att on, the garbage just goes
> > away. Sometime but less frequently I'll have the problem on 40m
> > with the SW BC. I have NEVER had it on any of the other bands
> > even during a major contest.
> > Believe me this is NOT a problem.
>
> Isn't this something you can tone down with the RF gain control?
>
> g.
>
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