[Lowfer] DBM choice

Mon, 8 Dec 2003 20:17:45 -0500

Stewart

I have a modified Kenwood TS 850 that shows no drift at 60 Khz as well as
10 Mhz
so the only drift problem would be at the LO. My converter uses a 4 Mhz
clock Osc
that is solid at 60 second dots,, not sure if I can get that lucky again 
 HAR
the 850 is set up to provide 70 Mw for VHF transverter so is ready to go
as well

In order to raise the LO level will probably include a MIMIC in the LO
line providing
it is stable,, not sure right now what is in the junque box. 

On the rcv mixer I termed the input, LO and IF out  with a 3 Db 50 ohm
attenuator 
in order to keep every thing happy and it apparently did the job. I
switched to an R 75 
because the IF rcv a ICOM 756 has a couple of cycle drift at 4 Mhz. Have
to see how far 
along I get on this project this winter right now the 144 beam is missing
half a 
reflector and the 160 meter L is wrapped around the Hazer and it is cold
or snowing. 
I think the Watkins Johnson mixer is a goodin and the price was right 

Bob  K3DJC

> The mixer should work fine.  Transmit mixers are usually not
> critical, especially when both inputs are clean signals.
> The sum term and any IM products will be at HF and easy to
> filter out.  There may be a little output at harmonics of the
> desired Tx frequency, but lowfer finals typically generate
> lots of those, anyhow.  They don't normally cause any trouble,
> because the resonant antenna attenuates them greatly, and
> power is very low.
> 
> However, stability is important at LF, and 1 ppm of drift at
> 3.6 MHz would become 20 ppm at 180 kHz.  Ideally, your 80 meter
> rig has a single reference oscillator, and you can use that same
> source (via divider, DDS, PLL, etc.) to generate the LO for your
> mixer.  That would prevent any drift from being multiplied.
> 
> If you plan to transmit using modes that demand really high
> stability, you may want to check your transceiver before building
> the downconverter.
> 
> 73,
> 
> Stewart KK7KA
> 
> 
> > Hi Gang
> > 
> > Picked up another DBM mixer which has a range from
> > 2Khz to 12 Mhz. This is the one I used for the rcv mixer
> > 
> > it is a WJ-M6H and has a noise figure of 5 Db, a SSB conversion 
> loss of 6
> > Db
> > the LO drive max is a +7 and the peak input power is a +17. I was 
> able to
> > get these
> > free so I dont know if they are still made or price but I hope to 
> use it
> > in a Tx mixer
> > to down convert 80 meter to LF. 
> > 
> > The rcv mixer works well so I hope it will work OK on Transmit
> > 
> > any opinions
> > 
> > Bob  K3DJC
> 
> 
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