FWIW, the HMC832 has FOM of -226. The best synth on a chip
now available AFAIK has FOM of -236. That's 10 dB better.
Rick N6RK
On 12/12/2018 10:46 AM, Dr. Ulrich L. Rohde via time-nuts wrote:
I did some phase noise measurement and the 8751 is much better then the rest on
the market
Sent from my iPhone
On Dec 12, 2018, at 1:20 PM, Bob kb8tq <[email protected]> wrote:
Hi
Just to save others the time digging, the 7851 uses a HMC832 VCO + fractional N
PLL on a chip as
the heart of its synthesizer. Yet another “way to go” if building a quick and
simple signal source.
===
No argument at all about other parts of the radio having their limits. PA
performance certainly is one
of those areas.
Bob
On Dec 12, 2018, at 12:42 PM, Dr. Ulrich L. Rohde via time-nuts
<[email protected]> wrote:
My feeling is
A Because of the low sunspot cycle the large signal performance of the RX is
less a topic, the ICOM 7851 dynamic range, synthesizer and frequency concept is
winning but expensive
B The power amplifier from 100 W to 1500 Watt need to be catching up to the old
Collins tube Amps with negative feedback, producing - 45 dB or better IMD
products.
The military amplifier are fast on , reliable , durable and expensive...
initially.
The noisy blower may be a bad thing.
I “only “ run 1 KW, and I am happy with it
73 de N1UL
Sent from my iPhone
On Dec 12, 2018, at 10:47 AM, Bob kb8tq <[email protected]> wrote:
Hi
Usually on HF, the issue is large signal rejection. Phase noise very definitely
gets into that part of things. Other components in the signal chain do as well.
Once the synthesizer is no longer the weak link in the chain, spending more
to improve it (vs spending on the other components) probably does not make
a lot of sense. Since the synthesizer is *far* from ideal, that sort of begs the
question of just how troublesome the other parts are and how much better a
device *could* be built.
This does seem to be wandering a bit from a Time related topic …..
It does illustrate the point that “good enough” may be way far away from
“pretty good” and yet even more distant from “as good as it gets”. The
question on any system is always “how good do you need / what are you
doing?” ….
Bob
On Dec 12, 2018, at 8:49 AM, jimlux <[email protected]> wrote:
On 12/11/18 3:26 PM, Bob kb8tq wrote:
Hi
As I said, just how rational using these parts in a radio …. not at all clear
to me.
Back when I went to school, stuff that was this noisy was not in the “greatest”
category.
That was a *very* long time ago.
Oddly enough best performance synthesizers have gotten better. (as the posted
presentations very clearly show). Just why a “high end” radio uses a less than
ideal synthesizer likely relates more to cost (even at a price of thousands of
dollars)
than to anything else.
Or "good enough" performance - driving to a 3 dB NF for a HF receiver while
maintaining good strong signal performance is probably not worth it
Indeed cost also drives things like GPSDO’s and GPS modules. We often are not
very eager to acknowledge that fact.
Bob
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