[time-nuts] Modern signal generators

[Bob kb8tq]

Hi

I assume 8751 = 7851 (says Bob who makes typo’s in about every second sentence :) ).

I’m not at all surprised it’s doing better than the radios with SiLabs parts. They dominate 
the market once you get to the “rest of the pack”. Of course those radios are half the price 
(or less) than the 7851.

Bob

> On Dec 12, 2018, at 1:46 PM, Dr. Ulrich L. Rohde via time-nuts <time-nuts at lists.febo.com> 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 <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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