[ARC5] CW/MCW

[Fuqua, Bill L]

  It really had not occurred to me before but one possible reason is that since radios of the day did not have product detectors.
Receiving CW required turning off the AVC, turning up the volume control and constantly changing the RF/IF gain for a suitable 
audio level. With out AVC you could not just leave the radio unattended monitoring for a CW signal, especially for a beacon.
  I just don't understand why they did not begin using a product detector earlier except that possibly they were concerned that
the BFO would leak into the earlier stages of IF and desense the receiver. 
  I have a HQ129X that I got years ago. I have several. Actually my first Novice station had one. Anyway this one had an additional 
switch added to it for a solid state (dual gate mosfet) product detector. It was tied to the original BFO and works great as does
the AGC. No leakage problems at all. 

73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of Roy Morgan [k1lky68 at gmail.com]
Sent: Monday, November 11, 2013 12:56 PM
To: tom at telmore.com; ARC-5 List
Subject: Re: [ARC5] CW/MCW

On Nov 11, 2013, at 12:39 PM, tom at telmore.com wrote:

>
> Seeing this talk off BFO's and CW/MCW I have often wondered what is the real advantage of using MCW other than if your receiver lacks a BFO control?

Tom,

One reason is that WW-II radios often had modest tuning capability, no CW-useful crystal filters, moderate bandwidth, and not so good stability.  So with all those factors, the MCW signal was easier to tune in and copy, and if any drift happened in either the transmitter or receiver, the signal would not be lost so easily,

In the case of radio navigation beacons, the receivers were homing on the signal with a loop and sense antenna using the steady carrier. The ID signals were AM modulated on the carrier and could be copied while the radio was in its normal mode.  A lot of trouble for the pilot can be avoided if you can both get the bearing and confirm you are tuned to the right beacon.

Roy

Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958

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