[Lowfer] Mid day EAR capture with push-pull J310 preamp

[wa3tts at verizon.net]

J.B. & All:  I picked up a couple of the SV1AFN push-pull MMBFJ310 preamp boards and got one working over the weekend.  These J310s are the surface mount
version with maximum dissipation of 350mw according to the data sheet.  SV1AFN web info says it should run 20ma per transistor maximum at 12V, but I was seeing
around 42 to 44 ma. The surface mount transistors also ran hotter to the touch than I was comfortable with, so I ended up with a 56 ohm resistor in the B+ line, which
dropped my battery voltage on the preamp board to 10.7V from 13.0 volt range. Total current was then around 41ma.  Here is the modular LF converter setup...

https://www.dropbox.com/s/44y2fmgeyc9jkph/LFCNV918.jpg?dl=0

 The transistors are warm to the touch but not at the pain threshold for me at a B+ of 10.7 volts. I would guessmate
120F or so for the transistor case temperatures with my finger thermomenter.

Anyway, here is the first EAR rx test with the push-pull J310 preamp with peak background noise at -81.8 from my NW EWE antenna...

https://www.dropbox.com/s/3dvpcolb98yezn7/EARM81R8.JPG?dl=0


Here is best rx capture level at -61.3 SNR

https://www.dropbox.com/s/berrpijp6597wkg/EAR61R3.JPG?dl=0


Here is EAR from a few days ago on my 2N3904 preamp. At the time, best background noise was around -71 peak in ARGO with EAR best at -54.1

https://www.dropbox.com/s/o7kv64mvqrrd2ap/capt00020.jpg?dl=0

So with the push-pull J310, EAR is  81.8-61.3 = 20.5 dB out of the noise, whereas on the 2N3904 preamp EAR was 71-54 = 17 dB out of the noise.

Given a typical NF for a 2N3904 is 5dB, the push-pull J310 looks to be 3~3.5 dB better in this initial test, or in the 2 dB range, which seems reasonable.

No OIP3 data was provided on the SV1AFN preamp. I did an initial 1dB compression point test at around 12 volts B+ the other day and it was around +18 dBm, but I want to test
the preamp again with a different attenuators on the signal generator and RF power meter.   Since the MMBFJ310s are not easily replacable like TO-92 package transistors, I do not
want to push the performance envelope too much.

The preamp board came with all the surface mount components installed. I had to wind and install the RF  transformers, install the RF connectors,  package it in my last Bud Box.  The 12mH choke in the converter setup pix  is a noise management precaution....I added a .001 feed through and 4.7uf NP cap to the B+ input before the 56 ohm dropping resistor to the preamp board...

SV1AFN preamp link info ...  https://www.sv1afn.com/j310preamp.html

Also note the plated through-holes for the mounting screw positions were not grounded. So I grounded them to the SMA connector pins with solder lugs that were cut to fit.
After a few soldering iterations on the +12V board connection, the copper pad lifted from the bottom side of the board.  So solder once and do it right the first time....

For $30 and change on eBay, it was a worthwhile improvement for my LF/2200m converter


73 Mike wa3tts