"gareth" wrote in message
...
"Michael Black" wrote in message
xample.org...
On Sun, 13 Oct 2013, gareth wrote:
Further information most welcome, thank-you
In the 1948 Radio handbook which I mentioned previously,
there are adverts
from a company by the name of Millen, and I assumed it
was the same guy
after he had left National.
Your comment about a phenolic intersperser is no doubt
some means of
isolating an
earthy contact?
It would be interesting to know from the Lamb patent
whether he proposed
therein the
technique of Single Signal Reception by the use of the
phasing control to
null
out the audio image, or whether this was something that
came about through
experience?
ONce again, "single signal selectivity" is credited to
the Lamb filter, everyone referencs that famous QST
article of his. You don't need the phasing control to
get the single signal selectivity.

Incorrect.

If the Xtal alone gave you single signal reception, then
there'd be no advantage
whatsoever in having the phasing control.

That the phasing control can be used to null out other
signals is the strong indication
that more than the one signal is getting through the Xtal.

Single Signal reception is the reference to the audio
image being phased out.


I have an RCA AR-88 receiver, this has a crystal filter
but does not make the phasing adjustment available although
there is one internally. The filter works quite well but the
lack of the phasing adjustment to null out heterodynes is a
distinct lack. In later versions of the receiver RCA did
bring the control out the front panel but, because its not a
balanced control, as is the Hammarlund and later Lamb
filter, it doesn't work nearly as well. I suspect RCA was
trying to avoid infringing the Lamb patent.
The original Lamb filter when set for high selectivity,
could cut out the audio image of a CW signal pretty well
but, of course, the phasing control could be set
specifically to null it out. Lamb wrote two or three
articles in QST in the early thirties about improving the
receivers available at the time and about single signal
reception.
You are right about the HRO not being the first receiver
with a crystal filter. I am not sure which was but an
earlier National receiver definitely had it as you point
out.
BTW, in searching for Lamb's patents earlier today I
came across one I didn't know about: its essentially a
mechanical filter using a rod with piezo electric drivers
and pickups. Lamb describes a variable bandwidth IF using
this filter for the medium wide band, a normal single
crystal filter for the narrow band and a conventional IF
transformer for the widest band. Curiously this patent is
assigned to RCA. I didn't note the patent number but all of
these can be found by searching Google Patents for James J.
Lamb.


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Richard Knoppow
Los Angeles
WB6KBL