[Amps] Pre-Distortion Linearizer

Roger (K8RI) k8ri at rogerhalstead.com
Sun May 5 23:53:06 EDT 2013


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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