SB 104 Frontend Boards...sensitivity

[talen]

For all you folks out there with (or working on) SB-104(A)s and
HW-104s, this is to provide some quantitative data on the frontend
boards (board "G") vs "sounds more/less sensitive" or "it's greatly
improved". While the sample size is small, I finally came across
3 frontend "G" boards to experiment with and thought you might find
the results interesting. I'm just sharing data and am open to further
suggestions and info on other aspects of the 104s....selectivity,
strong signal capabilities, etc.

Guess my net is:
  -- The HP quad mixer diodes work and are cheap ($2-$3 a quad set
     from Brad.Thompson at valley.net ) replacements for the FM-1100s
  -- The SBLs don't buy anything relative to sensitivity from my
     observations (maybe because the Heathkit toroid transformers
     are really pretty efficient and low loss)
  -- The 2N5109 can be "souped up" a little with an RF choke and
     resistor change
  -- The SB-104A board design is substantially better than the SB-104
     board design
  -- Don't use silicon signal diodes in the low level frontend mixers.

73s  Kees K5BCQ


*******************************************************************************
*******************************************************************************
RF gain fully advanced, CW mode (expected to be more sensitive
than SSB), "Measurements 65" signal generator on lowest setting
without external attenuators (approx 0.2uV output), attach a DVM,
measuring AC, across the speaker terminals, advance volume
control to get 30mV Noise level, measure Signal+Noise level, record
20log(S+N)/(N). All testing in a HW-104. Noise level of all cards
started out +/- 10mV of 30mV (except the one with 1N914s) and
were adjusted to 30mV since some cards obviously have more
overall gain than others.

Comparison to a Heath SB-301 is also given (only other Heath HF
receiver/transceiver available).

*****************************************************************************
*****************************************************************************
Results on 14.250Mhz (all trimmers peaked for 14.250Mhz):


HW-104 frontend card #1                                                       6db
-------------------------------------------------------------------------------------------------
   (older SB-104 design using FET Mixers....unmodified)


SB-104A frontend card #3                                                  14.8db
-------------------------------------------------------------------------------------------------
   (uses double balanced diode mixers.....unmodified)


SB-104A frontend card #2                                                  14.5db
-------------------------------------------------------------------------------------------------
   (original except: modified with 2 Minicircuits SBL-1 or SBL-3
    sealed mixers, replace silicon band select diodes with PIN
    diodes, replace 2N5109 collector 1K with 1mH RF choke,
    replace emitter 560 ohm with 100 ohm.....all per N2EO article)


SB-104A frontend card #3                                                  14.6db
-------------------------------------------------------------------------------------------------
   (original except: modified by replacing FH-1100 mixer diodes
    with 2 sets of HP 5802-2805 matched quad mixer diodes)


SB-104A frontend card #3                                                  16.3db
-------------------------------------------------------------------------------------------------
   (original except: modified by replacing FH-1100 mixer diodes
    with 2 sets of HP 5802-2805 matched quad mixer diodes,
    replace 2N5109 collector 1K with 1mH RF choke, replace
    emitter 560 ohm with 220 ohm)


SB-104A frontend card #3                                                     xxx
   Signal not detectable at 0.2uV, at 2.0uV  S+N/S = 6.7db
-------------------------------------------------------------------------------------------------
   (original except: modified by replacing FH-1100 mixer diodes
    with 1N914 Silicon signal diodes).


SB-301 Receiver (for reference)                                          15.8db
-------------------------------------------------------------------------------------------------
   (unmodified)

Listserver Subscription:listserv at listserv.tempe.gov - "subscribe heath 'name' 'call'"
Listserver Submissions: heath at listserv.tempe.gov
Listserver Unsubscribe: listserv at listserv.tempe.gov - -"signoff heath"