RadioBanter - Kiwa Shortwave Preamp and S/N ratio

Hi Steve,

When I owned my first AR7030 receiver in 1996-1998, I used a Kiwa preamp
with it. If you'll take a look at my AR7030 review on www.radiointel.com (or
elsewhere on the Web) you'll see that Craig at Kiwa measured a noise figure
of 11.8 dB with the radio's internal preamp on, and 10.3 dB with the Kiwa
preamp on (and internal preamp off).

This 1.5 dB improvement is too little to be noticed by ear, but the higher
specifications of the Kiwa device degraded the frontend performance (IP2,
IP3, and dynamic range) less than the AOR's stock internal preamp. Here are
the figures Craig measured on my AR7030 in his shop:

3rd Order Intercept measured at 12 MHz with the Preamp ON: +9.75 dBm
3rd Order Intercept measured at 12 MHz with the Kiwa SW Preamp: +19.5 dBm

I said the following in my AR7030 review: "Word is spreading among AR7030
owners about the usefulness of a quality preamplifier, particularly when
used on DXpeditions and in other low-noise surroundings. On a recent West
Coast USA DXpedition in Washington State, most participants used Kiwa
Electronics Broadband Preamplifiers and Shortwave Preamplifiers. Receivers
included the NRD-535, Drake R8 and R8a, ICOM R-71a and the AR7030. The Kiwa
devices provided audibly better S/N ratios on weak tropical band signals and
foreign (split frequency) mediumwave DX targets. I believe more strongly now
than when I first bought my AR7030 that the receiver can use a preamplifier
like the Kiwa models with excellent overload immunity and noise
characteristics. The AR7030's built-in preamp does not provide the same
level of improvement."

The key phrase here is "low-noise surroundings". At a Pacific NW coastal
DXpedition location, particularly in mid-winter, the bands can be
eerie-quiet. The band noise can drop the lowest during--and for an hour or
two after--local sunrise. If this coincides with a few days of quiet solar
activity, watch out! The opportunity to snag some excellent, weak DX is very
good... DX that would normally be obscured by band noise. It is in these
situations that a quality, low-noise preamplifier like the Kiwa model is
useful (compared to a mediocre preamp like in the stock AR7030). The
difference is not dramatic... in fact, it is slight, and may not even be
noticed by the casual SWL or MW listener. However, it is another "edge" in
performance for the dedicated DXer and a useful tool which surpasses the
preamps in most receivers.

Let me emphasize that the S/N ratio improvement with the Kiwa preamp was
*slight* (but noticeable), and ONLY when I was on DXpeditions to the coast.
At my home in the Seattle/Tacoma area, I could find no difference between
the Kiwa and the stock AR7030 preamp regarding S/N ratio due to the much
higher noise levels. However, I had fewer intermod products and garbage from
local powerhouse mediumwave stations appearing in the 2000-3000 kHz range
when using the higher grade Kiwa preamp.

This week I asked Craig about the questions in this r.r.s. thread, and here
was his response for the group:

"The Noise Figure of the receiver is established in the front end or the RF
amplifier. If an external preamp is included in the signal path that is
quieter than the internal preamp than the Noise Figure improves. The
internal preamp must be disabled for this to occur. I have measured the
Noise Figure of numerous receivers and an improvement using the Kiwa preamp
instead of the internal preamp is nearly always universal. If the internal
preamp is exceptionally quiet there will be no change. I have never found a
receiver where the Kiwa preamp degrades the Noise Figure. Will the owner
hear the difference? If the improvement is only 1-2 dB, I doubt if it could
be heard under typical/normal circumstances (urban environment with typical
noise levels). However, if the dB improvement is significant and if a super
low noise antenna is used the improvement should be noticeable when
listening to difficult signal conditions."

For a number of years now I've used a preamp module from Wellbrook
Communications which Andy Ikin built into the K9AY antenna control box he
used to market. This is an even higher performance preamp than Kiwa's, and
it has an IP3 of +43 dB and a 1 dB compression point of +25 dBm. This is one
very RF-sturdy preamplifier!

The bottom line? Most people won't notice the difference between a quality
preamp and an average one, but it does exist. However, for rummaging around
for DX at the noise floor in an exceptionally low-noise environment, you
want to use the best system components available.

Guy Atkins
Puyallup, WA USA
mod. IC-756Pro & mod. R-75
Kiwa MAP / ERGO
450 & 700 ft. West & NW Beverage antennas

wrote in message
oups.com...
According to Kiwa's website, their shortwave preamp will make your
receiver quieter. They claim that when you turn off your receiver's
internal preamp and instead rely upon the Kiwa preamp, you will have
fewer noisy circuits operating inside the receiver.

I find myself unmoved by this claim, since it would apply to *any*
external preamp--and most external preamps will do nothing to improve
S/N ratio, at least in my (limited) experience.

Of course, the Kiwa preamp also has a BCB rejection filter. I *do* see
how this could improve S/N ratio, but I'd like to hear some first hand
reports.

If you've used Kiwa's preamp, can you comment on whether it resulted in
a significantly improved signal to noise ratio?

Thanks in advance,

Steve