[ARC5] ARC-5s at 10 meters (was 400784741321)

[Kenneth G. Gordon]

On 16 Oct 2014 at 7:27, Ian Wilson wrote:

> I would be surprised if the Q of a solenoid in the HF region increases
> with frequency - for Cu, the skin depth between 1MHz and 10MHz
> decreases by a factor of more than 3; so, as a first-order approximation,
> the Q at 28MHz would be close to the Q at 8MHz (the increase in wL
> is more or less cancelled by the increase in r).

Thanks, Ian. However, I suspect that Neil didn't mean that the "Q" increased 
with frequency, but simply that the increase in frequency didn't affect the 
circuit "Q". Your and his explanation coincide.

> 
> In practice I suspect that the Q drops off faster than this because of
> the effects of distributed capacitance (which in effect requires more
> turns to achieve the desired inductance at higher frequencies, hence
> yet more loss).

Yes. I had thought of that too, and had wondered about it.

> The combination of tube gain falling off above about 10MHz together
> with losses in coil switching is presumably responsible for the "deaf
> as a post" performance for some classic boatanchor receivers above
> 20m....

Which brings up an interesting point: after I had finally gotten my hacked 
BC-454 to work properly at 10 meters, I was very surprised to find that the 
sensitivity at 10 meters was quite adequate. Although I will have to go back 
to review my notes, I recall that around a 1 microvolt signal was being easily 
copied there.

There was, of course, considerable noise, most probably from that horrid 
12K8 mixer, but the signal was easily discernible, and this was with the 
original 12SK7s in it.

Ken W7EKB