[time-nuts] Modern signal generators

[Dr. Ulrich L. Rohde]

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 <kb8tq at n1k.org> 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 <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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