[Amps] Pre-Distortion Linearizer

[Fuqua, Bill L]

   I have not read all of this thread, a lot said and I just not on computer much these days. 
However, a mulit-op contest station would benefit from a receivers and transmitters with low IMD as well
as low phase noise. While most operators would not. 
  However, I have observed that receivers that have fewer mixer and amplifier stages sound "cleaner" and
"clearer" than those many stages that the signal must past thru before it gets to your ears. 
It seems that many rigs are designed by committee with each designer responsible for some piece and
they seem to use "cookbook" engineering rather than spending time to optimize the design with only the
necessary parts to achieve their target. I am just amaze how complex, even setting aside the synthesizers,
cpus, and fancy displays, transceivers have grown compared to say a KWM-2 or SB-100. 
  As I said, just an observation. 

   73
Bill wa4lav

________________________________________
From: Amps [amps-bounces at contesting.com] on behalf of Roger (K8RI) [k8ri at rogerhalstead.com]
Sent: Sunday, May 05, 2013 11:53 PM
To: amps at contesting.com
Subject: Re: [Amps] Pre-Distortion Linearizer

On 5/5/2013 3:47 AM, Ian White wrote:
>
> You have a point, Joe; both transmitters and receivers fall into
> different classes of performance depending on the price range. But there
> is still no valid reason for any transceiver to perform significantly
> worse than the comparable "best in class".
>
> Stepping up to a completely different performance class does indeed cost
> money; but improving performance to equal the "best in class" is much
> more often about attention to detail.
>
> Because there has been such a market-driven obsession with "receiver
> numbers" like IP3, the best designers in the development team are
> working on the receivers, while the design of the transmitter is
> apparently being left to the tea boy. There is a real lack of managerial
> - and indeed, moral - imperative to design the best possible transmitter
> that can be produced within the given budget.
>
> Another aspect of the "$900 rig problem" is that most of these
> transceivers were originally designed for the domestic market in Japan,
> which is much more heavily biased towards mobile operation due to the
> population density. Many aspects of performance are sacrificed for the
> sake of compactness as well as low cost; but in addition to that, they
> are specifically designed for operation with relatively inefficient
> mobile antennas. That means the receiver needs to be quite sensitive and
> the transmitted IMD will be 6-10dB further into the noise. But when the
> same radio is used at a fixed station with even a simple wire antenna,
> the receiver becomes overly sensitive and has poor strong-signal
> handling, while the transmitted IMD looks very poor indeed.
>
> Some years ago, the Japanese manufacturers were quite surprised that
> what they thought of as "mobile" transceivers were being marketed in the
> West for fixed-station use; but now these $900 rigs have become a major
> part of the Western market. Beginners reasonably ask why they should pay
> more... and I don't think that anyone is telling them.

And I don't think it would make much of a difference if someone did.
It's not just beginners who use these little rigs in base stations.

Our local group is heavily involved with the NWS and the local EOC from
more than just a weather approach as are two adjoining counties and
their hams.  All three have informally standardized on one of those
small rigs for mobile use.  Probably between a third and a half also use
those rigs from home.  Only a few of us are DX chasers running QRO and I
dont think any of us are using the small rigs from home, but I do know
one who is a serious traffic handler and working regularly on 5B-WAS
with one.  I think a number of the traffic handlers are using the small
rigs.

So between the 3 counties, as an educated or SWAG I'd say we probably
have 30 to 50 of those small rigs operating from home stations.  Several
are pushing notoriously over rated amps on the bands that are noted for
short tube life.  So you start out with a 897D or IC7000 pushing 4 811As
for more than they are worth you do not end up with ideal band
conditions.  A number of these stations are pushing their budgets to get
a use 897D let alone a used set of 4 811As.

It's  not just that many can't afford more than the $900 dollar rig,
there are a lot more who can't justify one in the car and a better rig
in the house

It's all they can afford so I can't fault them for the rigs they are
using but I can for the way they use them. However many of the
experienced try to "shoe them the way" and why to follow it.

IM figures are difficult to find but I found a QST review of the IC7000
listing 3rd order IM at -33db, but they are regarded as being overly
optimistic.

I haven't been able to find even a QST review on the 897D.  The E-Ham
reviews were ... well... shall we say written by those who called it
well constructed and said some were giving it a bum wrap, but I do not
call a rig where the jacks are held only by the solder joints to the PC
board as well constructed.

IOW I did not find the E-Ham reviews to offer any real substance.

I'll leave the realistic IM figures for both rigs to someone who has
done a realistic measurement.

73

Roger (K8RI)


>
>
> 73 from Ian GM3SEK
>

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