Before I did a lot of trouble shooting on that Century 21, I'd make sure it
was connected to a proper aerial and see if the birdies are still audible.
Testing for birdies with no antenna connected gives no meaningful results
because usually they will be weaker than ambient band noise.
Don't borrow trouble!
73, Mike N4NT
----- Original Message -----
Sent: Tuesday, August 19, 2003 1:38 PM
Subject: [TenTec] Century/21 Model 574 receiving what's not there?
> WARNING!! I'm prolix when I use a keyboard!
> I'm a pretty new ham who started as a General because I primarily
> want to work QRP CW on HF. I was looking for an old rig that I could
> pretty much plug 'n play on HF with a key, an antenna, an antenna
> tuner and an SWR meter.
> I picked up a Century/21 Model 574, serial number 574-0253, at a swap
> meet yesterday in the hope of acquiring a rig that I could use for CW
> QRP by just keeping the Drive control turned way down. The seller
> (who wasn't the previous owner; a silent key was) said it powered up
> and the digital readout presented sensible numbers, but he hadn't
> checked it out further.
> I opened the top and bottom covers and it looked really good inside--
> no mods or repairs that I could see. The aux XTAL for 28.5 to 29.0
> MHz was in the socket, and the seller had the owner's manual.
> When I got it home, I turned the Drive control all the way down and
> kludged an excuse for an antenna connection into the SO-259. (As a
> newbie, I don't yet own a decent antenna or a single 50 ohm coax
> cable with PL-259 connectors.)
> When I turned it on and started listening, my first thought was that
> someone had put an internal crystal calibrator into the receiver
> circuit. I could hear what sounded like unmodulated carriers on all
> 5 bands at various points throughout the dial and could also hear a
> (perhaps) 5 Hz beep at some points on the dial. I can zero-beat all
> these things, but sometimes there were 2 "signals" pretty close to
> each other, separated by not a lot of Hz (I don't exactly have
> perfect pitch).
> The idea of a crystal calibrator soon fell by the wayside because
> the "signals" weren't zero-beating on multiples of 25 KHz or 100
> KHz. Likewise the 5 Hz pulses weren't on any frequency that made
> sense to me--for example, one place I could hear the 5 Hz was 14242
> KHz or so.
> I can hear real CW signals and listen to SSB QSO's, but the zero-
> beatable 5 Hz beeps and things that sound like unmodulated carriers
> are quite audible with no antenna connected, the antenna connector
> shorted or unconnected, and the RF "Gain" control set all the way
> down (CCW).
> I wonder if the 5 Hz stuff is coming from the Digital Readout board.
> If so, how does it show up as 5.0 - 5.5 MHz IF?
> The "signals" I'm describing are not making their way from some
> transmitter on the ham bands. I have 2 general coverage shorwave
> portables with BFO's and don't hear these "signals" on either of my
> portables; just on the Century/21. (Only 1 receiver is turned on at
> a time just to make sure that one receiver isn't picking up signals
> from another of my radios.)
> Any ideas on how to get rid of these pseudo-signals? My first
> thought, since I don't have a bench full of test equipment, is to
> start replacing electrolytic capacitors all over the place since the
> unit is around 25 years old. Other suggestions would be most welcome.
> Tnx & 73,
> Irving M. Prais