Kiwa Shortwave Preamp and S/N ratio
 

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

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
Why would a preamp not help s/n ratio? If it amplifies the signal along with
antenna noise, then there is less amplification to be done by the radio
itself and the stage noise in the radio will be reduced. It should improve
S/N ratio.
B

what is happening is that the noisy preamp in the receiver is being
REPLACED with a less noisy preamp from kiwa. therefor overall there is
less noise.

it is totally logical, Craig has made an "expensive" high quality
preamp to replace the low cost financially constrained consumer
pre-amp.

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

Unless the noise figure of the Kiwa preamp is significantly better than the
NF of the one in the receiver, there will be no improvment in S/N- it's not
magic, it's math. At HF S/N is hardly a concern anyway as the noise floor is
not device limited but atmospherics limited. If you hear an increase in
noise on your receiver when you connect the antenna, you are already seeing
the limit.

Dale W4OP

I don't think I've *ever* connected an antenna to any receiver without
hearing an increase in noise. Is the goal of improving the S/N ratio
really that hopeless? I've heard great things about the Kiwa
preamp....it that all just hot air or does it really live up to its
claims? Are you guys speaking from experience with the Kiwa unit?

Steve

jimg wrote:

i don't thjink i've ever heard anything goofier. you cannot improve on
the s/s at the receiver input without altering the antenna. given a
reasonable impedance match from the receiver to the antenna, that's
it. and it's not hopeless, it's just what it is. if there were no
atmosphereic noise or propogation effects, swl would be kind boring.

as far as your receiver, most receivers noise floors are so far below
the antenna s/n that there is no improvemnt in your dxing capability
there...and why playing with your antenna can make such a diff.

btw, there are ways to improve the performance dramatically, but
wideband amps are not the answer..whereas very narrow band rf amps
are...especially if they're LN2 cooled along with the antenna
pre-amp...but then you don't have enough money for this scheme.

now the kiwa design like other LNA's is very basic and uses a shunt
feebback two transistor approach. other use cascoded mos devices
(called dual gate by non-engineers)..all are very low noise designs
and give moderate gain/ in the case of kiwa, you get 10dB gain and a
reasonable NF (noise figure) (p.s. your cell phone gets better) ...
but 10dB is practically nothing (you got a 10dB rf attenuator on your
rcvr?) and usually will not change an overall sinpo from 2 to 3.

20dB is better, but if noise at the antenna dominates, the snr remains
the same.

having an rf lab with about $2M of equip to play with, i built a nice
little preamp with built in programmable rlc bandpass filtering....and
even then there is little appreciable improvement (on an old r1000) on
"real" sigs buried in noise...

some mornings though, when the background noise is low, the preamp
boosts weak sigs to a more audible level. non-linear adaptive LMS
noise cancellation does the rest...

if you dont have an rf front end worth a damn, it might help...and a
bcb hp filter might too....but in general, you paid enuf money
for a more than adequate rf front end...the rest is the sunspot cycle,
your propogation conditions, your patience and tenacity...


jimg phdee


I don't think I've *ever* connected an antenna to any receiver without
hearing an increase in noise. Is the goal of improving the S/N ratio
really that hopeless? I've heard great things about the Kiwa
preamp....it that all just hot air or does it really live up to its
claims? Are you guys speaking from experience with the Kiwa unit?

Steve

jimg
Oregon
USA

The preamp can improve NF if it has enough takeover
gain..........................in most cases, this is not necessary. A much
better way to go is to have a 1st mixer that has a low conversion loss or
good NF in the first place. Any amount of RF amplification that you add
ahead of that mixer decreases the dynamic range by the same
amount.........for instance, if you add 10dB of gain ahead of the mixer,
your 1dB compression is degraded by 10dB, your IP3 is degraded by 10dB,
etc,etc,etc.
As an example, you can use a Mini-Circuits TAK-3H as your 1st mixer. The 1dB
compression point on this device is +14dBm and the IP3 of this mixer is
+28dBm. The tradeoff here is that +17dBm (50mW) of LO power is required to
properly "turn on" the diodes so that good dynamic range and conversion loss
figures are met. The SSB conversion loss on this device is right around
4.7dB. This is roughly, but not exactly equivalent to the NF. Add in 2dB of
loss for the input filter and you have a system NF of approximately 7dB.
This will allow you to hear a signal down to around .04uV. You do need to
have a good post mixer amplifier that follows the mixer, and a diplexer to
follow that mixer. Since the diplexer provides some selectivity, you will
not have noise at the image frequency degrading the system NF. It is not
expensive to employ this scheme; I don't know why manufacturers don't
generally do it. Exceptions are some of the solid state Collins equipment,
the Drake R7, TR7, R8. Some of the manufacturers use a quad JFET 1st mixer.
This mixer can have an IP3 of +30 to +40dBm. Examples that use this design
are the Kenwood TS-50, TR570, Racal 6790/GM, AOR-7030, Yaesu FT1000.
The big thing here is setting up the proper gain distribution in the system.
Whenever possible, keep all of the amplification AFTER the 1st mixer, and
you will be able to take advantage of the full dynamic range of the mixer.
I think that the Drake R8 has a NF of 10 to 12dB, as does the AOR-7030. For
receiving below 30MHz, this is fine, because in most areas, 15dB is the
amount of excess noise that you will encounter.
I hope this helps to explain why you don't need a preamp, unless you are in
an extremely quiet location such as northern Wisconsin, up in the ore
deposit regions, or out in the country where the excess noise is a bit
lower. When I was living out in the outskirst of Cedar Rapids, the area was
extremely quiet RF wise, so a super sensitive receiving system was helpful.
Now that I am back in the Chicago area there is so much noise that this type
of receiver isn't as necessary. The background noise from the thousands of
furnace controllers, factory equipment, etc, bring up the background noise
quite a bit.

Pete

"jimg" wrote in message
...
jimg wrote:

i don't thjink i've ever heard anything goofier. you cannot improve on
the s/s at the receiver input without altering the antenna. given a
reasonable impedance match from the receiver to the antenna, that's
it. and it's not hopeless, it's just what it is. if there were no
atmosphereic noise or propogation effects, swl would be kind boring.

as far as your receiver, most receivers noise floors are so far below
the antenna s/n that there is no improvemnt in your dxing capability
there...and why playing with your antenna can make such a diff.

btw, there are ways to improve the performance dramatically, but
wideband amps are not the answer..whereas very narrow band rf amps
are...especially if they're LN2 cooled along with the antenna
pre-amp...but then you don't have enough money for this scheme.

now the kiwa design like other LNA's is very basic and uses a shunt
feebback two transistor approach. other use cascoded mos devices
(called dual gate by non-engineers)..all are very low noise designs
and give moderate gain/ in the case of kiwa, you get 10dB gain and a
reasonable NF (noise figure) (p.s. your cell phone gets better) ...
but 10dB is practically nothing (you got a 10dB rf attenuator on your
rcvr?) and usually will not change an overall sinpo from 2 to 3.

20dB is better, but if noise at the antenna dominates, the snr remains
the same.

having an rf lab with about $2M of equip to play with, i built a nice
little preamp with built in programmable rlc bandpass filtering....and
even then there is little appreciable improvement (on an old r1000) on
"real" sigs buried in noise...

some mornings though, when the background noise is low, the preamp
boosts weak sigs to a more audible level. non-linear adaptive LMS
noise cancellation does the rest...

if you dont have an rf front end worth a damn, it might help...and a
bcb hp filter might too....but in general, you paid enuf money
for a more than adequate rf front end...the rest is the sunspot cycle,
your propogation conditions, your patience and tenacity...


jimg phdee


I don't think I've *ever* connected an antenna to any receiver without
hearing an increase in noise. Is the goal of improving the S/N ratio
really that hopeless? I've heard great things about the Kiwa
preamp....it that all just hot air or does it really live up to its
claims? Are you guys speaking from experience with the Kiwa unit?

Steve

jimg
Oregon
USA

here is how Craig (the designer) describes it:

The receiver's Noise Figure may be improved when using the SW Preamp,
especially if the receiver's preamp can be disengaged.

The SW Preamp has excellent signal overload immunity. It typically
measures 20 dB better than the average receiver. Third Order Intercept
or ICP3 is a measurement of signal overload characteristics. The SW
Preamp ICP3 measures +34 dBm. A typical table top receiver measures +4
to +10 dBm. The Drake R8A specifies an ICP3 of +10 dBm with the preamp
engaged.

The balanced input allows proper termination to balanced antennas such
as a two wire beverage antenna, or T2FD antennas. Kiwa will soon have a
phase switching control unit available for balanced beverage antennas.
This control unit would connect to the SW Preamp output and the
CT-Center Tap connection providing the ability to switch the receive
pattern of a two wire beverage antenna. (In one position the receive
pattern would be from one end, the other position would switch the
receive pattern to the other end.)

Reception below 1.8 MHz is possible when using a long-wire or beverage
antenna by connecting the receiver input to what is the 50 Ohm Input.
In this configuration the input transformer is acting as an impedance
matching device to the 50 Ohm Input and signals are passively coupled
to the receiver bypassing the BCB Filter and Preamp.

Price: $109.00

Claimes are claimes.Clamies don't mean **** unless you buy one of them
claimes and see/hear the proof of the pudding for yourelf.I can claime
any damn thing,but what does that mean? Step Right Up,Ladies and
Gentlemen,, this snake oil will cure evreything that ails ya! Only one
dollar a bottle!
cuhulin

I'm enjoying these posts about why the Kiwa preamp should / should not
be of much use to me, but it's a little surprising that not a single
soul from RRS has stepped forward to say "I tried the Kiwa preamp and
HERE'S WHAT HAPPENED...." I have less technical expertise than any of
you guys, so when you disagree with each other about the usefulness of
this device, I'm not in much of a position to conclude that one side's
right and the other's wrong (though I DO enjoy the posts, just the
same...maybe I'll learn something). However, if someone just said, "I
used this preamp and it did/did not work", this is a piece of
information I'd know how to 'digest'.

I will say, though, that the mere fact that there's no clear consensus
on whether the Kiwa would help with S/N makes me uninclined to put down
over a hundred bucks for it.

Steve

I can claime I have a two foot long dick.All the wimmins around the
World would be beating a path to my door.If they come (CUM) here,I would
turn the table upside down and tell them to help themselves.
cuhulin

do you know how to spell ? (besides being gross)

I think you should buy the preamp if you think you will like it. I think
that the reason nobody on this NG seems to have the Kiwa preamp is because
they all have decent receivers. With a halfway decent receiver, you don't
need a preamp. The trend in recent years has been to use NO RF amplification
ahead of the 1st mixer. In the tube days, an RF amp was generally needed,
because of the use of pentagrid convertors, etc. Exceptions were the R390
(at least the 1970s unit I had), which used a 6C4 1st mixer, the Squires
Sanders IBS Superhet and their amateur version (SSR-1 or SS1-R?), which used
a 7360 balanced mixer. If you have a good NF, there is no need for a preamp.
A case in point...........even though the Kiwa preamp, which is very good,
has an IP3 of +34dBm, the gain that the preamp provides still degrades the
IP3 of the receiver itself by that same amount. +34dBm is ok for a high
level preamp, but it is possible to design an RF preamp that has a +40dBm
IP3.
In all fairness to Kiwa, the preamp is very reasonably priced. I once looked
at a schematic of the regenerative preamp for the Kiwa loop.............a
very good design. The things they were doing with the high performance
ceramic filters were very good. Too bad Murata decided to discontinue
everything but their 4 and 6 element ceramic filters.

Pete

wrote in message
ups.com...
do you know how to spell ? (besides being gross)

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

In article ,
"Pete KE9OA" wrote:

I think you should buy the preamp if you think you will like it. I
think that the reason nobody on this NG seems to have the Kiwa preamp
is because they all have decent receivers. With a halfway decent
receiver, you don't need a preamp. The trend in recent years has been
to use NO RF amplification ahead of the 1st mixer. In the tube days,
an RF amp was generally needed, because of the use of pentagrid
convertors, etc. Exceptions were the R390 (at least the 1970s unit I
had), which used a 6C4 1st mixer, the Squires Sanders IBS Superhet
and their amateur version (SSR-1 or SS1-R?), which used a 7360
balanced mixer. If you have a good NF, there is no need for a preamp.
A case in point...........even though the Kiwa preamp, which is very
good, has an IP3 of +34dBm, the gain that the preamp provides still
degrades the IP3 of the receiver itself by that same amount. +34dBm
is ok for a high level preamp, but it is possible to design an RF
preamp that has a +40dBm IP3. In all fairness to Kiwa, the preamp is
very reasonably priced. I once looked at a schematic of the
regenerative preamp for the Kiwa loop.............a very good design.
The things they were doing with the high performance ceramic filters
were very good. Too bad Murata decided to discontinue everything but
their 4 and 6 element ceramic filters.

The only reason I can see for a pre-amp would be a very low gain (small
size) antenna such as a small loop. A table top radio with a full size
antenna would probably not get much benefit from an amplifier. The only
other exception to this was the very low noise surroundings example
previously posted.

--
Telamon
Ventura, California