[time-nuts] cheap frequency extension for timepod

[Bob kb8tq]

Hi

I would *think* that the phase noise out of the down converter channel would be the DUT + LO. If indeed you
have DUT A + LO B and DUT C + LO D, you then have a lot of A + B vs C + D stuff to sort out ….

Bob

> On Oct 17, 2020, at 2:48 PM, John Ackermann N8UR <jra at febo.com> wrote:
> 
> FWIW, I have done PN measurements at 144 MHz with the TimePod and a Frankenstein's laboratory lashup of 80 MHz ULN, HP doubler to 160 MHz, HP mixer, and several amp and filter blocks.  As far as I can tell, it worked pretty well; at least, I could discern the PN difference among several sources, some of them quite good.
> 
> Not sure why you are doing two oscillators/mixers, though.  I used a 5 or 10 MHz reference directly into the TimePod, and the DUT fed through the mixer.  No need to increase the frequency of the reference to match the DUT.  But if you do want to mix both the REF and DUT channels, wouldn't it be better to use a single source to drive both mixers?
> 
> John
> ----
> 
> On 10/17/20 8:59 AM, Gerhard Hoffmann wrote:
>> I'm trying to make a quick frequency extender for a timepod.
>> MCL PSC2-1 power divider, 2* SRA-1  7 dBm ring mixer, 2 DIL 80 MHz-oscillators
>> The oscillators can drive the ring mixers with just a coupling capacitor and 50 Ohm
>> load limiting resistor. It is still a square wave at the LO port, but the diodes in the mixer
>> would square it up on their own.
>> When there is no 5V-power, the oscillators are off and the LO inputs are connected
>> to SMA connectors via the normally closed contacts of two reed relays.
>> Then the whole thing is passive and needs two external synthesizers.
>> Before I continue with the material I had in the junkbox, a quick question to those
>> of you who have done that already:
>> Are 7 dBm mixers like SRA-1 good enough or is 17 dBm an advantage worth the
>> driver amplifiers? The usual signal generators max out at 13 dBm.
>> I have 2 17 dBm SRA1-WH, but it would require slaughtering something unimportant.
>> How close must the oscillators be in frequency?
>> Have a nice weekend,
>> Gerhard, DK4XP
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