[AReU] Converter News

[w4tas]

I have been very busy tonight testing all of the converters that 
we have obtained from various sources. I have also ordered 
some parts to finish the modification on some of these converters. 
The new signal generator I obtained at Orlando is just the ticket 
to check sensitivity and I can use the spectrum analyzer on the 
output and check the response curves of the input filters. 

Individual converter news is as follows:

California Amplifier 130001:

This converter has come up in sensitivity nicely. It is very 
close to the Transsystem units. I don't think you could tell 
the difference when listening on the satellite although I 
could detect a small difference in noise figure. 

This is the type I loaned to Mike that didn't seem to 
have much sensitivity in the tests last Saturday. With the 
signal generator and spectrum analyzer I tuned the 
interdigital filter between the last RF amplifier stage and 
the mixer for maximum response at 2400 MHz. This is what 
is causing the insensitivity on the unit that Mike has. The filter 
also has a relatively fast drop off below 2400 MHz which pretty 
much completely eliminates the image at 2112 MHz. With the 
filter modification and the IF amplifier modification to increase 
the gain below 200 MHz it is HOT. I ordered crystals today 
to move the IF to 144 MHz. 

California Amplifier 31732: 

This one was no surprise. With the Teflon tape modification 
on the filter it was as good as the first one I modified. I have 
the crystal ordered for this one also. This crystal and the 
crystal for the California Amplifier 130001 are identical. 
International Crystals tells me they will be shipped in about 
two weeks. 
This is the converter that Al is using at present and should be 
a really good one. 

Transsystem 3731: 

I thought this one was a looser but I talked to the Transsystem 
specialist today in Texas and he gave me the low down. It turns 
out that the input filter and the pre-mixer filter are pretty good 
attenuators at 2400 MHz. The good news is that they can be 
re-tuned by adjusting a set screw on each filter. You have to 
be careful not to go too low in frequency and start picking up 
the image but the signal generator coupled with the spectrum 
analyzer did a fine job of setting them up. 
I will order the crystals for the 3731 converters tomorrow. I 
think they will be here in about a week. 

Ed and I purchased one of these converters as well as Fred. 
Don't worry guys. These units are top notch and are easy to 
get to work. Fred, you will have to get your converter to me 
for a make over. 


Radar-Imm: 

This was mounted on a BBQ grill antenna owned by Al and I 
had never seen one like it. It uses a different crystal frequency 
in that the multiplier figure is 64 instead of 256. Fortunately all 
of the other frequencies are the same as the other converters 
I have tested and the general design is similar. I had to bypass 
the filters in the IF amplifier like the California Amplifier 130001 
to get the gain up below 200 MHz. I couldn't check the sensitivity 
because it has no coaxial cable input. It only has the dipole 
antenna and the reflector. The only way to test it would be 
on an antenna range or put it on the dish and listen to the 
satellite. The IF output is 122 MHz for 2400 Mhz input. An 
ICOM 706, Yaesu FT 847 or other general coverage 
receivers could be used to see if it was worth buying the 
crystal to convert it to a 144 MHz IF output. I tried to look at 
the frequency response with the generator and spectrum 
analyzer but I couldn't get a stable signal in the work shop. 
That is a task better suited to the "wide open spaces" to 
eliminate reflections. The only problem with this unit would 
be the response of the filters. I will continue to ponder this 
problem and try to get a good filter response check. 

Looks like just about everyone is just about ready for the 
downlink!!!

73

Tony