[ARC5] OT? bc-348 bfo question

[Meir WF2U]

Fer,

First of all the BC-348 was not designed to receive SSB. Receiving SSB is a
bonus owing to the fact that there is a BFO in the receiver :-) ...
The manuals don't define the amount of BFO injection. However, according to
the manuals and by correct operating procedure of any receiver without a
product detector but simple carrier insertion to the detector, CW is
supposed to be received with manual gain control and not with AGC. The
reason is that the BFO signal will reduce the gain if it's stronger than the
signal coming into the detector as the AGC detector can't differentiate
between the received signal and the BFO signal.
The way to go around this in receivers with separate RF and AF gain control
is to use manual gain control - no AGC, audio gain maximum and gain
controlled with the RF gain. In case of the BC-348 the RF and AF gain
controls are on the same shaft, therefore, as you discovered, the best
reception is with MGC and the gain control is at the minimum position which
gives the clearest audio.

Nothing is wrong with your receiver; it's simply the way it was designed to
be used on CW.

73, Meir WF2U
Landrum, SC


-----Original Message-----
From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On
Behalf Of Fernando - LU2DFM
Sent: Friday, September 13, 2013 11:29 AM
To: arc5 at mailman.qth.net
Subject: [ARC5] OT? bc-348 bfo question


Sorry if this is OT here.

I'm repairing and aligning a BC-348 (E, M or P variant, don't know
exactly which).

The set is going on very well on AM so far, however the BFO injection
level seems to be too low for SSB on strong signals. It's possible to
get SSB on the headphones with MVC and _very_ low RF gain.

All voltages and resistors values are ok around that stage with and
without BFO on. The xtal filter is ok too (bandwith with xtal on is about
1-2 kc).

The 2nd IF/CW osc. is the 6B8/VT93.

Anyone knows what the level of the BFO is supposed to be? 

Thanks.

-- 
73 de Fer, LU2DFM
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