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RE: MicroWave: 1296 Transverter design advice

> From:          "David Robinson" <robinda@nortelnetworks.com>
> To:            "'davemetz@muscanet.com'" <davemetz@muscanet.com>
> Subject:       RE: MicroWave: 1296 Transverter design advice
> Date:          Sat, 27 Feb 1999 22:55:09 -0500

> > Dear Dave,
> > 
> > Your right.  I guess the question is "how good is the third harmonic
> > suppression"   of the transmitter? So far I've been able to build filters 
>>with 60-70db of  suppression of the second harmonic on 222Mhz. 
>> I should be able to obtain as much or  better of the third (unless 
>>something is going on that I don't understand, that's sure possible :-)).
> > 
> > My plan is to use a three or four pole helical resonator to clean up the
> > 432 signal.   What do you think?

[Robinson, David [RICH5:7466:EXCH]]  

> 	it not the cleanliness of the 432 source to worry about. A mixer is
> a non linear device and multiplies as well as it mixes. therefore even if
> you feed a 432.1 signal into it with all other signals 100db down

> 	[Robinson, David [RICH5:7466:EXCH]]  the mixer will generate 1296.1
> and 1296.3. you may have to grossly under run the mixer to minimise the
> effect but it needs considering
> 	a similar problem exists with a 144 to 432mhz transverter, one
> company did for a short time produce a transverter by just mixing with
> 288MHz, but had to withdraw it from the market for the above reason and
> launch a different design that went via 28MHz
> 	dave 
> > I don't want to use two meters as the I.F. since that's my receiving I.F.
> > for the 2.4Ghz  converter.  So, I don't want to be transmitting in the 
same IF band that  I'm receiving in.  Any ideas?
> > 
> > --73-- David WA0AUQ

Dear Dave,

Good point on the mixer.  I wonder how many db down the multiplication spur would
be from the desired output?  Lets say I'm using a +7dbm mixer with +7 going into both
the L.O. and RF ports.   Any ideas?

I had not considered using a 28 Mhz IF due to the tougher filtering problems.  Although
this was the popular IF in the past.  I could start out by building prototype filters and 
testing them to see what kind of image suppression I got.

Another possible route would be to convert my 2.4Ghz receive converter (a DEM) to
a 432Mhz IF and use the two meter rig as the 1296 IF.  I was planning to rebuild the
2.4Ghz converters L.O. anyway.  Any problems with that arrangement?

--73-- David WA0AUQ


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