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Re: Transverters with *70cm* IF's



 > From:          tlang@freeway.apana.org.au (Tony Langdon)
 > Date:          02 Feb 00 20:44:01 +1000
 > Subject:       Re: [amsat-bb] Transverters with *70cm* IF's
 > Organization:  Fidonet: Freeway Usenet <=> FTN gateway 
 > To:            amsat-bb@AMSAT.Org

 > 
 > Hello Dave.
 > 

 > 
 >  DM> Now comes the tricky part, how to get on 1.2Ghz for the uplink.
 >  DM> I could use a converter to mix my 70cm signal up to 1.2Ghz.  However,
 >  DM> I am told that there will be "problems with the third harmonic of
 >  DM> 70cm." That is, the possible third harmonic of my 70cm radio will mix
 >  DM> with the output of the upconverter mixer producing spurs.  How serious
 >  DM> this potential problem would be I do not know.  It would take some
 >  DM> experimenting to find out.
 > 
 > I think it's worth attempting though.  I have a 2m to 70cm transverter, which
 > should have the same potential problem.  This is a 20 year old commercial
 > model, which performs quite well.  However, it is worth noting that the Tx side
 > of the unit uses double conversion (2m -> 28 MHz -> 70cm).  Perhaps this is to
 > minimise the possibility of harmonic bleedthrough.

I think you are correct.  Otherwise why do the extra conversion stage?
Maybe someone else reading this message can shead some light on the
problem.  Anyone out there???
 > 
 >  DM> Another consideration is the problem of generating a useful amount of
 >  DM> power on 1.2Ghz.   The only route I have found is to use ERA MMIC amps
 >  DM> to produce 7mw of drive.  Then use M57787 hybrid amp (7mw in gives
 >  DM> 1.5W out) to drive a M57763 (1W in gives 18 watts out).  Cost for the
 > 
 > We have a locally available set of kits which will provide a total of 10W SSB
 > on 1.2 GHz.  Just a matter of when to purchase the kit and start building.

Is there more information available on this kit?  
 > 
 >  DM> two amp is $170!   The current plan is too have the converters LO and
 >  DM> mixer in the shack.  Pipe the RF up to the antenna at low level and
 >  DM> have a ERA-x buffer stage overcome the loss of the feedline.  The PA
 >  DM> stage would be at the antenna to reduce loss of the those expensive
 >  DM> watts at 1.2Ghz.
 > 
 > My converters will be at the antennas too.  The antennas themselves will be
 > portable affairs.  I hope to procure a tripod or similar to stand them on.
 > 
If you do, consider the stability of the tripod carefully.  A conventional
camera tripod is not designed for holding a large load like a radio and
an antenna array.  They blow over in the wind!   You might want to consider
something like the portable telescope mounts that I have seen.
They are a 4" OD post about 4-5' high.  At the base are four legs that 
extend about 2' each.   The legs can be folded up against the post by
loosening a bolt.  At the end of each leg is a foot on a leveling screw for
fine adjustment of the leveling.  They are not all that large to carry,
and are very robust.  No reason that any decent metal worker could
not build one in short order.
 > 
 > I'm following the thread with interest... for obvious reasons. :-)
 > 
 >  DM> I suspect that it will take me a good two years to build all of the
 >  DM> stuff I need.  Till then, see you on mode U/V!
 > 
 > I'm hoping to be operational within 18 months.  As for Mode U/V, it'll depend
 > on if I can get enough antenna gain out of a portable station for these bands.
 > :-)  Also need another transverter (10-2m or 10m-70cm) so I can tune the two
 > bands independently.

 > 
 > Tony
 > 
 > .. otted lab rat!
 > --
 > |Fidonet:  Tony Langdon 3:633/284.18
 > |Internet: tlang@freeway.apana.org.au

--73-- David WA0AUQ

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