[time-nuts] Modern signal generators

[Bob kb8tq]

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 <time-nuts at lists.febo.com> 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 <kb8tq at n1k.org> 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 <jimlux at earthlink.net> 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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>> 
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> 
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