[MRCA] BC-348 Help

[Ray Fantini]

Thousand years ago when I was still in high school I had an APA-10 panadaptor connected to a BC-348Q
I did a coupling capacitor from the cathode of the first IF amplifier and brought that out via the front panel, think that I may have modified the internal cathode bypass too. Back in the seventies there were no reservations about modifying BC-348 receivers like today. They were both cheap and plentiful.

Ray F/KA3EKH






From: mrca-bounces at mailman.qth.net [mailto:mrca-bounces at mailman.qth.net] On Behalf Of DSP3
Sent: Monday, February 11, 2019 5:33 PM
To: comcast <kg2bz at comcast.net>
Cc: Ray Fantini <RAFANTINI at salisbury.edu>; mrca at mailman.qth.net
Subject: Re: [MRCA] BC-348 Help


Ray,

With appropriate kudos to Joe, WA3EJT et al, one uses 1/2 the BC-348 IF frequency and couple it into the mixer of the Q-5er, either ARC-5 or SCR-274-N.  Physically, I make an insulated loop, about 1 1/2" in diameter and locate it at the base of the 3rd IF in the BC-348.  No soldering.  Using RG-175 coax, I run the coax out the back of the BC-348.  For convenience, I use either a set of RCA phono M/F connectors or a BNC set.  Then, run another length of RG-175 (etc) into the Q-5er and connect it to the grid cap of the mixer tube via about 10pf.  Attaching the signal here effectively bypasses the front end which would otherwise serve to attenuate the desired 915 kHz IF frequency of the BC-348.  Then, tune the Q-5er to +/- 407.5 kHz to pick-up the IF output of the BC-348.  The Q-5er IF tuning rods can be selected for whatever bandwidth you desire.  The math for the above is 407.5 kHz + 50 kHz (Q-5er IF) X 2 = 915.  It works like a charm and the only physical connection is the grid cap.  Some say one can get BC-348 IF signal leakage via the headphone jack, but that has not been my experience.  Finally, and if you want to be a bit more elegant, mount an RCA F on the rear, top cover of the Q-5er and run the coax to the grid cap.  Using a submin clip, attach the center conductor to the grid cap.  That way, service can be done without difficulty.

Jeep K3HVG


On 2/11/2019 1:06 PM, comcast wrote:
Jeep how would you set up the Q5 with the BC 348 without hacking into the receiver? how and where would you physically Connect into the IF circuit and how would you run it into the command set receiver?
thanks Jeff

Sent from my iPhone

On Feb 11, 2019, at 10:08 AM, DSP3 <jeepp at comcast.net<mailto:jeepp at comcast.net>> wrote:
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