[Premium-Rx] Clean LOs

[Brian D. Comer]

Francis
 
I think that the best synthesizers today use both DDS and PLL. I am
currently working on a synthesizer for 2.4 GHz for military use using
the AD9956. This could turn out to be a very good device. This device
has all the circuitry required for a clean synthesizer, with the
exception of the VCO. In the project that I am doing with AD9956 I have
yet to get the device programmed completely so have not done any tests
on spectral purity. The device is probably too small for most amateur
work and I cannot assemble it or remove it from a board even though I
have a fairly good set up and can handle 0402 parts with little
difficulty. Analog devices have a demo board for this part that could be
very interesting but I do not have one.
 
 I believe that the main problem with the RA6830 synthesizer is that it
does not use enough bits for the D to A in the fractional N loop coupled
with very poor ground loops in the 60 Hz supply. 
 
 73 Brian
 
KF6C
 
-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Carcia, Francis
A HS
Sent: Monday, February 14, 2005 5:26 AM
To: premium-rx at ml.skirrow.org
Subject: RE: [Premium-Rx] Clean LOs
 
    Brian,
What would you consider a good synthesizer? I agree the layout of the
6830 synthesizer needs some help. I have not found the correct setting
of the analog compensation. Also The phase noise gets worse when the AUX
output is connected. I suspect the grounding of the VCO connectors and
cables need termination to the case. I plan to build my own VCO. I have
a mini circuits VCO running
4X that I might try. I would use local voltage regulation. I have
checked a number of receivers and yet to find one better. The closest
was the old WJ 8718.   fc 
-----Original Message-----
From: Brian D. Comer [mailto:bcomer at cox.net]
Sent: Friday, February 11, 2005 10:26 PM
To: premium-rx at ml.skirrow.org
Subject: FW: [Premium-Rx] Clean LOs
 
 
-----Original Message-----
From: Brian D. Comer [mailto:bcomer at cox.net] 
Sent: Friday, February 11, 2005 4:00 PM
To: 'Michael O'Beirne'
Subject: RE: [Premium-Rx] Clean LOs
 
I do not support the idea that frequency synthesizers are necessarily a
problem and would not consider the using of anything else for a high
performance receiver today. That is not to say that they are necessarily
good and I find the ones in the RA 6830 an example of a bad design or at
least bad implementation. There are of course may other very poor
synthesizers out there.
 
On the great HP 8640, many years ago I had access to one when it had
only just been released to the market. I took it home and used it as an
LO for a home brew 2 meter transceiver. The reports that I received were
that I had very bad FM on the my signal. The HP 8640 uses a frequency
locked loop which can very easily be frequency modulated by strong
signals, so take care when use it as an LO.
 
73 Brian
 
KF6C/G3ZVC
 
-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org
[mailto:premium-rx-bounces at ml.skirrow.org] On Behalf Of Michael O'Beirne
Sent: Friday, February 11, 2005 1:49 PM
To: Premium-Radio
Subject: [Premium-Rx] Clean LOs
 
Dear All,
 
One quick idea to see what a really clean LO can do for a receiver might
be to disable the internal synthesiser and feed in some RF from a good
HP8640B genie or similar from R&S.  G3OSS (Angus McKenzie) did this at
VHF with a professional VHF receiver and was much impressed.
73s
Michael
G8MOB
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