[Milsurplus] BC-9 Loop Test: Scratching My Head.

[Kenneth G. Gordon]

On 10 Feb 2017 at 4:13, Hubert Miller wrote:

> The Q whether high or low isn't a dynamic figure while the tube characteristics are.

True.
 	
> Q is just not responsible for what you are seeing. 

Well, I disagree, at least in part. It most certainly could cause at least SOME of what he is 
seeing since the "Q" directly effects the impedance, which is reflected into the tube's plate 
circuit. Differeing "Q"s will cause differing offsets.

> We assume that all radios had to have netting ability.

Now THAT is a question I had thought about too. In most military comms with which I am 
familiar, the receive frequency is very often NOT the same as the transmit frequency. In 
fact, sometimes it is far off. I am thinking of the common way the AN/GRC-109 was used for 
instance. In fact, I vaguely remember something suggesting this in that original document 
that Dave shared with us on how to use the BC-9 in service.

Is it possible that this +/- 12 kc difference between the TX and RX frequencies was well 
known at the time, and was used effectively for their comms? "I'll transmit on such and such 
a frequency, and will listen on such and such a frequency". ?

> Maybe that was not the case with this radio. 

Yes.

> You could still use it to communicate. Like the example of the early Forest Service 33 MHz radios
> that transmitted and received on differing frequency. 

And the common use of the AN/GRC-109, and many others too.

> Miller effect appears at the grid. Don't ignore the larger change in capacitance and impedance
> at the plate of the tube. 

See above.

> As i suggested, you may want to try increasing the plate feedback ratio capacitor, C1-lower.
> That will be a palliative, not a cure, though.

On the other hand, I also suspect that there MAY be something we have missed in either 
the circuit itself or in the operation of the equipment. Perhaps there was a "field change" or 
modification which we don't know about.
 
> Or, assuming you really want on-frequency operation, you could operate the set with the same
> B+ on transmit and receive, say something like 90 volts max, maybe. Yes, your power out will
> go down to 1/3 or 1/4, but you'll still be able to make demonstration QSOs.

Yes. That is another good idea.

But, folks like Dave and I believe the equipment should be operable in its original condition 
and shouldn't need any mods to make it work for amateur uses.

Ken W7EKB

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