[NLRS] What's the problem with UHF (& microwave) contesting?

[Dr. Gerald N. Johnson]

On 3/11/2016 9:14 PM, Glen Overby wrote:
>
>
> On Fri, Mar 11, 2016 at 6:06 PM, Mary Brown<maryalanab at gmail.com>  wrote:
>
>>
>> Cheap way to get on 144, 222, 432 for those who only have an HF rig
>> http://transverters-store.com/ 144&  222 are $75 432 is $95, sure you need
>> an amplifier stage after these if you want more than qrp but it will get
>> you
>> on the higher bands... they are around 3 watts out. They sell an attenuator
>> board also. Add some switching from attenuator to the transverters and you
>> have 3 bands in a box. If enough people ask they may add 902 and 1296!
>>
>
> I have two of these transverters: 50mhz and 144mhz.  I put the 2m
> transverter on my spectrum analyzer and looked at the output; at full
> power, it is HORRIBLE!  Spurs were close in enough that there was no way I
> was going to filter them.  They were better at low power levels, but I
> don't know how much of that would return if it was run into an amplifier.
> I didn't try it.  They now sit in a junk pile.

That can be the transverter or the spectrum analyzer or both. Mixers and 
amplifiers do have limits on signal level where they begin to clip and 
to make spurs near the main frequency. Third order intermod shows up 
first. With two tones their third harmonics generated in the mixer or 
amplifier clipping show up at the fundamental spaced their frequency 
spacing from the original inputs. The next step should be running the 
same test with at least 10 dB more attenuation between the transverter 
and the specturm analyzer. If that cleans it up, the SA was being 
overdriven. If that doesn't clean up the signal then the IF drive needs 
to be reduced, or the idling bias of the output stage be increased.

MMIC chips like the MGA-1105 or ERA-5 put out more power and the more 
modern ones like the PGA-103+ do more power and have a great NF for 
receive at the same time. WA3IAC is selling out his line of PGA-103+ 
amplifier kits and parts. WA5VHF and G4DDK are selling similar kits, and 
there are low noise broad band amps from China on epay every day at 
reasonable prices compared the WA3IAC's prices that have been.

73, Jerry, K0CQ
>
> Glen, kc0iyt
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