[ARC5] BC-459A Status

[Kenneth G. Gordon]

On 5 Oct 2013 at 13:29, Mark K3MSB wrote:

>     Well, no real progress as to why my 40M BC-459-A has such a horrid on the air tone.

>From what I have read so far, it sounds to me as though you have RF from the output of the 
transmitter getting back into the power supply, then effecting the oscillator. What you have is 
unwanted feedback from the output of the transmitter inputting to the VFO from some 
source.

I would make absolutely certain everything is securely bonded to some ground-plane, as 
Dave Stinson mentioned he does in his case.

What makes me think of this is that in my own case, I have a DX-35 and I use a VF-1 with it. 
The tone and keying on 80 meters is perfect. Output from the VFO for using the DX-35 on 80 
meters is on 160 meters.

Tone and everything else on 40 WAS just terrible, yet the VFO alone sounded perfect, and 
yet I use the exact same VFO with my HW-16. With the HW-16, tone, drift, etc, are perfect 
on 40, and even perfectly acceptable on 15 meters.

I fixed the problem with the DX-35 by doing the following: 1) carefully bypassed every lead 
which connects from the DX-35 and its power supply which feeds the VF-1 at the entrance to 
the VF-1. 2) used shielded cabling from the DX-35 to the VF-1, grounded carefully at both 
ends. 3) made certain that the VF-1s cabinet and front panel were securely bonded, 4) used 
double-shielded cable to connect the VF-1s output to the DX-35.

This cured the problem and the DX-35/VF-1 now sounds as good on 40 as it did on 80.

>From your scope photos, the VFO output looks about as perfect as it could be, and with the 
finals in place and no antenna, it still looks very good. 

The fact that you are using an absolutely minimal antenna on your monitor receiver would 
show you what the signal actually sounds like. Adding a "better" antenna to it would simply 
cause overload and you would not be actually hearing what the signal from the TX sounds 
like, since sometimes that kind of overloading can cause the RECEIVER to exhibit chirps and 
clicks on the TX signal when, in fact, they are not there.

As I said, from what I can see and from what I have read about this problem, I am just about 
convinced that you are experiencing un-wanted feedback from the TX output getting back 
into the VFO some how.

The source MAY be very difficult to actually track down.

Since the 80 meter TX sounds so good, while the 40 meter one sounds bad, you might wish 
to VERY CAREFULLY examine and compare both transmitters to see if there is something 
different about their shielding or internal connections or wiring or the number of screws, etc.. 
It might be something very easily overlooked. As I remember it, one of your TXs is the Navy 
type with shunt feed in the final, and the other is an Army series-fed model. Even so, they 
should sound equally good on the air.

Ken W7EKB