[AMPS] Receiver tests in the past........

[Hans Goldschmidt]

1-01-15 16.46, skrev Peter Chadwick på Peter_Chadwick@mitel.com följande:

In the ARRL Extended Reviews they show curves on receiver intermodulation
vs spacing of the two measuring tones. The FT1000MP is very good at close
spacings if I remember right.

Now, when we have more and more of features DSP generated at the end of the
if chain, you notice the lack of selectivity close to front end. I have
noticed in a TS 570 for example pumping of the agc and s-meter readings from
not heard signals close to the cw-signal I want to hear. Inserting a cw
filter and the problem disappeard. I have not the ARRL extended test on the
TS 570 avaiable right now, but I am sure this measurement curve will show
intermods closer the wanted signal than in the FT 1000MP? Will the new TS
2000 perform in the same poor way as the 570?

This leads to what I  question myself right now regarding the new TS 2000
from Kenwood: Do they have a crystal filter at the higher if to keep close-
in signals out of the if chain? I do not know although I have taken the
owners manual from Kenwood on the net and, as it is nowadays, there is no
technical description of this very interesting rig.

Following the tradition of the FT 101, a very bad big signal performer but
that was the most sold rig years ago, the manufacturers know most ham
customers do not care of and understand  big signal performance. So, to
simplify manufacture and put as much selling features as possible in the
rig, they put a dsp at the end of the if that you can program for everything
than making a cup of tea. But, are these modern rigs better than an old
DRAKE R4B or C that have selectivity right after the first mixer?

YAESU has finally recognized the need of front end selectivity (
preselectors) in their new Mark V that was standard in older rigs like the
R4B. Now, Eurpean hams  have much less second order qrm in this rig from
strong broadcast stations located in Europe.

Yes, round filters and not so sharp filter flanks give a much better
sounding audio. I know: I recently purchased ( 75 dollars complete
including original mike and power supply!!) an old love from 1976. An ICOM
IC 701 with two 6-pole ( I guess) filters in cascade. Has a terrific sound
in tx and rx because of less phase distorsion.

If you want to see REAL commercial made performance tests, you have to look
into DL1BUs tests in the 1970 and 80s. The test of the TS 930 was specially
fantastic. All filter curves were plotted at several band pass positions
including the depth of the notch filter. Gunther was the one of the pioneers
whose critics lead to the advanced rigs we have to-day. He had an antenna
measuring site and made a lot of commercial made tests on ham antennas.

Prosit de Hans SM5KI


> 
> Ian says:
> 
>> The difficulty with DDS spurs is that the amplitudes and
>> frequencies change (pseudo) randomly with frequency.
> 
> No they don't. See the paper by Danielli of UCLA in IEEE (I think is it was
> Circuits and Systems) back some ten years or so. They are predictable,
> although
> it's complicated to do it. They tend to be worse where the multiplicand of the
> minimum step size is of a value tending to 2*(n+/-m) where m is a small
> number.
> This is a Diaphantine equation, of course.
> 
> I would have thought that anybody doing a real review these days would be
> using
> IEEE bus controlled generators, not a 608 or an 8640, so a sweep shouldn't be
> that hard to do.
> 
> 73
> 
> Peter G3RZP
>> ----------
>> 
> 
> --
> FAQ on WWW:               http://www.contesting.com/FAQ/amps
> Submissions:              amps@contesting.com
> Administrative requests:  amps-REQUEST@contesting.com
> Problems:                 owner-amps@contesting.com
> 
> 


--
FAQ on WWW:               http://www.contesting.com/FAQ/amps
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com