Hej Verner:
Some days ago I raised the same questions on the amps: what happens with the
relation peak SSB pep level to phase noise and spuriouses when you lower the
power output in a modern transceiver to suit the drive power needed for a
linear on VHF/UHF? Where you have high gain beams and more sensitive
receivers than on short wave. As you know, you can in an IC706 or IC 746 do
this in the menu. The 746 has a good relative quite synthesizer and few
spurioses ( not better than the very old ICOM IC 202 that used a vxo, I
guess).
A warning: the IC 706 has a relative noisy synthesizer and garbage and noise
is heard on both sides of a signal when using the PS35 switched power
supply. In a OH0 contest station they run their IC 746 on batteries in two
meter contests to avoid garbage and noise from their power supply.
I often asked myself how much noise sidebands are generated in the output
transistors of a rig? Looking through test reports, I have a feeling that
figures of synthesizer noise are better in the receiver than transmitter.
Using VMOS fets should then give less noise, no?
What about high frequency getting into the diodes of an amp power supply? I
remember seeing reports of noise coming from hf modulating linears. Maybe it
is therefore caps are still used across the high voltage diodes in high
voltage supplies to shorten out hf? For the same raeson the HEATH SB 1000
maybe used a rfc choke in series with the diodes?
I am a buyer of these ancient IC 202 or 402 from around 1973??
Paa gensyn de Hans SM5KI
----------
>Från: "oz5tg" <oz5tg@post2.tele.dk>
>Till: <amps@contesting.com>
>Ämne: Re: [AMPS] RE: ALC
>Datum: tor 17 feb 2000 08.21
>
>
>>Message text written by "Steve Thompson"
>>
>> Mine certainly offends with a nasty little overshoot of a few 100 us on
>> rising edges whenever there is any ALC action. It depends on the excess
>gain
>> in the transmit chain and varies with power and frequency. When wound down
>> to drive a transverter, it makes the rig too dirty to use in our contest
>> station with spitching covering about 30kHz. Over 24 hours, the gain
>varies
>> somewhat and it's asking for trouble to have all the ops keep tweaking the
>> mic gain.
>>
>> The problem is that the ALC loop response is crudely slowed with a
>> capacitor, presumeably to keep it stable. One day I'll find some spare
>time
>> to try and improve it.
>
>Hi Steve et.al
>
>I find it very interresting that You report problems with the FT990.
>Recently
>we had a serious problem here with an amateur that started using his FT990
>as a backend for a 144MHz transverter.
>
>When the power was turned dovn to 2W for the tranceiver the phasenoise from
>the 990 was big enough to put out a -60dBc. With a 1000W PA that resulted
>in S9 broadband noisefloor covering several MHz!
>
>With 100W/2W in/out from an attenuator/dummyload the noisefloor was lowerd
>the equivalent 14dB which made it possible to tolerate with good antennas
>pointing away from him.
>
>Tests with a spectrunanalyzer pointed out the FT990 as the offender. During
>keydown-
>no modulation the 28MHz signal had a 60db S/SN relation and with modulation
>the ratio
>improved with the rising signal. The problem may be related to the internal
>AGC/ALC.
>He sold the FT990 immediately.
>
>Now, a -60dBc noisefloor may be a very small problem on HF, but on VHF and
>up
>I believe that -90 dBc for an avarage station is OK, and -100 to -110dBc for
>a "contest-
>grade" station will do.
>
>Any comments?
>
>73 de OZ5TG, Verner
>
>
>
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