Hi Helmut
I think you are incorrect. an old analog radio is usually miles ahead of
the little chip radios >= 1MHz phase noise...
and fractional spurs. Happy to bet my house on it. Are you ???
The IC9700 is not very good at 1 MHz offset. Sur eit is good on RX but
not good on TX wideband.
It is because the microwave VCO in the chip has insufficient Q, and is
contaminated by the other currents on the die and chip, that you cant
do much about unless you move it off chip ! spurs and noise leak in.
For an integer setup, the loop bandwidth doesnt go much beyond 400kHz,
and so it relies on the VCO performance at 1MHz-10 MHz which isusually
poor.
For a fractional setup, the very idea of a SDM is that noise is moved
from the low freq to the high freq, so you cannot run high loop
bandwidths anyway . You are limited to < 60 to 80kHz in most cases, and
so this does nothing for the 500kHz to 5 Mhz ish phase noise .
and as all the chips are designed for DC to daylight, there is NO
bandpass of anything, meaning wideband noise is radiated over a whole
band or octave of spectrum.
On 8/04/2020 10:00 pm, Helmut Oeller wrote:
Hi Glen
Sorry for disagreeing!
You probably refer to ready assembled boards. The bottleneck are NOT the chips
or their design. The problem are the cheap VTCXOs on PLUTO or LIMESDR. When
applying an external low phase noise reference at 40 MHz the concept hits e.g.
the praised IC9700. On 1.Ghz the RX and TX phase noise of the a/m Lime was
measured far better (offsets at 100Hz up to 200 kHz).
With these advanced chips from Analog Devices or Lime microsystems cleaner
microwave radios can be designed than any of these old analoge radios + noisy
transverters.
Take care.
73, Helmut, DC6NY
-----Ursprüngliche Nachricht-----
Von: glen english [mailto:[email protected]]
Gesendet: Mittwoch, 8. April 2020 12:48
An: [email protected]
Betreff: [Freetel-codec2] A warning on using single chip transceiver chipsets.
While on this discussion, I think a caution neds to be applied here to the
single chip radios about, IE transcievers used for DV hot spots, and SDRs like
Lime SDR.
Their wideband phase noise is TERRIBLE. They polute the band . And many do not
understand the implications and effects. As well as wideband noise, they use
fractional synthesisers and their spurs are many and broad over a wide spectrum
These type of single chip transceivers are not designed for operating in a
space where there are sensitive radio service in the same 20 MHz....
Well they are but the limit is an ERP of about 100mW before harmful
interference is caused to, for example the local repeater.
Happy to discuss/ advise, suggest / comment.
So, from this POV, its pretty hard to do a low cost simple chipset that can be
connected to a 25Watt amplifer and any sort of decent antenna. There are
options, but they're not necessarily expensive and they need to be carefully
implemented.
cheers
glen VK1XX
On 4/2/2020 7:07 AM, David Rowe wrote:
Hi Mooneer,
As for the SM2000, it might be useful to resurrect at some point. Or
perhaps include the lessons learned in a future project. :)
There is a lot of scope for open source DV and VHF/UHF
experimentation, as Jeroen and several others are showing us.
The idea of a low MDS VHF/UHF stand alone radio embodying some of the
concepts of the SM2000 is still intriguing to me:
+ efficient modems and low noise figure, so it runs DV in the <
+ -130dBm
range (20dB better than FM and 1st gen DV)
+ LPCNet style wideband codec
+ something stand alone/portable/HT form factor minimal hardware
+ lockdown/high performance modem (avoid chipsets with
the modem inside)
+ a few watts power output, proper PA filtering that meets commercial
+ specs
But not sure what hardware I'd use these days.
Cheers,
David
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au mobile : +61 (0)418 975077
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