[hpsdr] Possible 5 band VHF transverter?

[Helmut, DC6NY]

Hi Conrad,

whatever you plan, keep  phase noise below -120 dBc/Hz at 10kHz offset. Assume
that level, SSB bandwidth of 2,7 KHz and a strong S9+40 dB (-53 dBm, VHF
definition) carrier in 10 kHz distance: your RX channel will be influenced
by -53 + (-120 + 34) dBm = -139 dBm noise. That is absolutely tolerable. But
things become critical already at -110dBc/Hz for weak signal detection. The
MAX2870 can be used up to 70cm Band without restrictions.

73, Helmut

-----Ursprüngliche Nachricht-----
Von: hpsdr-bounces at lists.openhpsdr.org
[mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Conrad Farlow
Gesendet: Samstag, 16. März 2013 00:15
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] Possible 5 band VHF transverter?

***** High Performance Software Defined Radio Discussion List *****

Andrew I rejected the SI570 because I couldn't lock it but I must admit 
the idea of using a broadband uwave VCO/Synth and dividing to get better 
phase noise may not be a bad idea at all.

Actually measuring phase noise is a problem for me, all the modern 
spectrum analysers that I have at work use similarly poor LO sources. 
I'm glad that people are talking about this stuff. As I explained it is 
early days for me and I am more than capable of doing a U-turn! 
Sometimes several times a day.

73

Conrad

On 15/03/2013 22:32, Andrew wrote:
> Hi Conrad,
> Whilst it's a shame to throw away the fantastic phase noise 
> performance of Hermes by using a PLL with internal VCO as they are so 
> poor, its a good call for you as they are quite easy to work with and 
> as you say, you don't actually need the performance of a crystal and 
> the frequency agility is a bonus for a multi-band design.
> As a matter of interest, the SI-570 is somewhat superior and would 
> give you phase noise performance at 10kHz offset of about -132dBc/Hz 
> on 144MHz but you can't phase lock it to an external reference so 
> probably a bit limited.
> I too am looking at designing a transverter for Hermes as my main 
> interest is VHF/UHF, I say main interest but actually Hermes has got 
> me quite a bit interested in HF also these days!
> I need it for more demanding applications like contests so will be 
> going for a more traditional but up to date design using a crystal 
> based oscillator and diode ring mixers.
> I had an idea to combine the outputs of two transverters say for 144 
> and 70MHz with different IFs so that with the two or more receivers in 
> Hermes I could monitor two bands at once!
> Hope you project goes well.
> 73's,
> Andrew
> G4XZL
>

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