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trans systems 3733 filter mods....



I finally was able to make the mods to the 3733 in order to add
a 2450 +/- 50Mhz to it.

I have little or no test equipment, so my tests before and after
are probably a little gross for most of the folks on the list.

Photos of the completed mods are as follows:
Filter after the LNA: http://www.flochart.com/tsmod1.jpg
Input strip line before the LNA: http://www.flochart.com/tsmod2.jpg

Observations BEFORE the mod (only mod was the stub removed)

Generate a low level signal on 2401 (50.020 x 48).
Received signal S7 with converter dipole 3 feet from generator.

Generate a low level signal on 2155 (50.116 x 43).
Received signal S7 with converter dipole 3 feet from generator.

Generator off.
Received buzz and hum modulated signals between S7 and S9+20
every 30 to 100Khz from 2400 to 2402Mhz.
Noise floor is at S3.

The modification was very similar to the mod made by N4IP 
where he removed the first input filter, and replaced the
second filter with a Murata 2450 +/- 50Mhz filter.  I used
the same pc board material he used (part # MMICTEF from DEMI).
It was cut to fit, and copper foil was used to fill in
parts of the DEMI board, as well as provide for good mounting
and grounding.  I found the copper foil at a local arts and
crafts store. Michaels was the name of the store.  A little
thought was required to allow the board to fit nicely, since
the machining in the 3733 has uneven mounting areas.
Specifically, the top mounting holes are higher than the bottom
mounting holes.  Its a bit difficult to describe, but a
quick examination with the filters removed will prove
enlightening.  Using the copper foil along the top edge of
the boards worked well.  The filter that I found (that I could
actually obtain), was the TOKO 4DFA-2450T-10.  Digikey part #
TKS2610CT-ND.  

As you can see, my techniques are not as clean as Pieter's, 
as I don't have the appropriate tools.  I also had to find
replacement screws that were shorter than the original ones.
The bottom edge screws are 2.5mm standard pitch, about 5mm long.
The top edge screws are #2-56 about 1/4" long.

Surprisingly, after I was done, the converter still worked!

Observations AFTER the mod:

Generate a low level signal on 2401 (50.020 x 48).
Received signal S7 with converter dipole 3 feet from
generator.

Generate a low level signal on 2155 (50.116 x 43).
Not able to detect any signal with converter dipole 3 feet
from generator.
Not able to detect any signal with converter 1 inch from
generator.

Generator off.
Received steady carrier at 2401.247Mhz at S5, 2401.136 at S3,
2400.040 at S9.
No other signals heard from 2400 to 2402Mhz.  Noise floor is
between S1 and S2.

I did attempt to peak the gain by slightly moving the inductor
loop at the input of the LNA.  It didn't appear to make any
difference, so I bent it back to its original position.

These observations seem to show that the modification
worked without any ill effects.  I have nothing to measure
the gain nor the noise figure.  All I can tell is that
it still appears to work.

Tomorrow morning I'll put the converter back on the bbq dish
and see what happens.  I'll post my results.  It appears I'll
have a pass tomorrow with a relatively good squint angle.  If
I can get outa bed in about 6 hours things should be about
as good as they'll get for my squint.  Hope to hear you guys
on the bird.

Kevin
N0BEL
kevinu@flochart.com

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