On Tue, 27 Aug 2013, gareth wrote:

"Percy Picacity" wrote in message
...
In article ,
"gareth" wrote:
"Percy Picacity" wrote in message
...
In article ,
"gareth" wrote:
But the fact remains that for those who understand the use of a
crystal
phasing control in pre-1950
receivers that the questions as posed above are as completely
informative
as
is necessary.
And you have had your answer - the tuning of the BFO has no effect on
the phasing control and vice versa. Do you not believe the answer?
Stating the bleeding obvious which we all knew any way is about as useful
and as relevant as quoting Newton's laws of motion; for neither are an
appropriate
response to the query as originally put.
I refer you page 79 of the previously mentioned book.

Sorry, perhaps you could tell us what the question was again. I thought
you were asking if there was an advantage to tuning the BFO half way
between the wanted and unwanted signals. There isn't.


There is. You get single signal reception for CW despite the wide bandwidth
of
a trnasformer-only IF strip.

No. single signal reception comes when you actually have decent bandwidth.
You can get that from IF transformers, if the IF frequency is low enough,
all those receivers that had a final IF at 50 or 85KHz.

As I said, you don't even need to have the notch, if you adjust the filter
"right" the notch is never there. You still get single signal
selectivity, because the other image is knocked out by being out of the
passband of the filter. The notch feature just adds to the thing.

You could just string a bunch of RC amplifiers together, be they triodes
or bipolar transistors or FETs, and then put matched crystals from the
"cathode" or whatever to ground. The crystal acts as a very selective
bypass capacitor, very low impedance at the signal frequency, so gain
happens then, and high impedance elsewhere, so gain tapers off. It's not
perfect and the selectivity requires a lower IF, but it's a simple scheme.
I've thought of making a WWV receiver that way, just some stages of
amplification with 10MHz crystals, and a diode detector.

Or pick some crystals all on the same frequency, and make a ladder filter.
Some have even worked on those so you can actually use the same crystals
for narrow (CW) and wide (SSB) reception, though sometimes it seems easier
to just use parallel filters, pick a frequency where the crystals are
cheap.

Michael VE2BVW