HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Take a look in the latest issue of the ARRL Antenna Book. Chapter 5 is
devoted entirely to loop antennas, and the chapter includes information
about small loops. At the end of the chapter is a nice sized bibliography.

TRABEM wrote in message ...
[stuff]

Getting back to last nights study session. Spent a couple of hours in
my 1987 ARRL Handbook and the remainder on the web looking at real
life loops published there. The web aspect was really disappointingly
devoid of technical jargon, it seems like most of the loop authors
just threw something up and it seemed to work-the end:: Do people
just throw stuff up without understanding what they're doing, or do
they understand and just fail to document the theory??

The Handbook tour was almost as bad. Very little was said about loops
except that which applied to the full wave resonant loop and how it
can serve as a driven element in a 1 lambda 'guad' type radiator.
Other than the theoretical wavelength, the correction factor for wire
diameter, there was not more than 2 paragraphs written with useful
information on short loops such as I am trying to put up.

[stuff]

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

TRABEM wrote:
"I didn`t price it yet, but I need more technical information!"

There`s a better approach than high "Q" capacitors for a VLF loop. It`s
been available since the year 1912 and much used soon after its
invention.

Edwin H. Armstrong, 1890 - 1964 was radio`s most productive inventor. He
invented regenerative control in 1912. I think he awakened his sister in
the middle of the middle of the night screaming : "Eureka, I`ve found
it!" or something to that effect. It wasn`t ubique for Howard Armstrong
to discover things. Following controlled regeneration, he discovered the
principle of the superhet in 1918, superregeneration in 1922, and the
complete system of frequency modulation in 1933. He would battle RCA and
Sarnoff for his entire life over control of his discoveries. I recall
seeing a photo of the battery portable radio Howard built and gave his
bride as a wedding present on an IEEE magazine cover.

Ever since 1912 there have been regenerative circuits introducing a
fraction of a receiver`s output back into its input to enhance its
amplification and sharpen its selectivity. Some of these are called "Q"
multipliers.

A "Q" multiplier is an oscillator circuit which has its regenerative
feedback adjusted just below the point of oscillation. It amplifies the
signal many times and shrinks the apparent bandwidth the tuned circuit
accepts. I`ve seen them used for reception of WWV at Boulder on 60 kHz
and for other low frequencies. This seems easier than using super parts.
Use some positive controlled feedback in the loop circuit. Adjust it for
convenience.

Best regards, Richard Harrison, KB5WZI

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Interesting Richard, thanks.

I read about these early pioneers years ago when I first became
interested in ham radio and was fascinated by the history of early
radio. There was a recent PBS program on the topic too, which I very
much enjoyed.

Regenerative receivers are all that you say they are, and more. If it
wasn't for the blasted gain control which has to be constantly
twiddled, they would be more popular today I'm sure. Don't they have
limited ability to separate the individual sidebands though, so they
are more suited for AM and very narrow bandwidth CW?

I'm intrigued however.....

Lately I've been working with a QSD based receiver and am very
impressed with it's simplicity and degree of performance. There are no
non linear mixers, IF's, detectors or IF transformers, so high
performance receivers are quite simple to build using this technique.
In general, no rf stage is needed (or desired). All of the 'gain'
comes after the detector, which is actually a high speed analog
switch. But, recovering the audio without DSP based software (usually
a sound card) is very difficult, needing large amounts of selective
audio filters slowly tailor the audio response to an appropriate
selectivity. Maybe some regeneration could be used to simplify this
fairly complex analog filtering.

N7VE's high performance direct conversion receiver (the NC2030) has a
highly detailed explanation of the post QSD audio using a hardware
approach rather than the more typical computer/sound card approach.

It's good reading if you're interested in clean sounding cw without
ringing and without over processed audio filtering crud mixed in..

While the job is simplified by modern op amps, it still takes a lot of
stages of low Q filters to make the audio sound clean and crisp. A
single high Q audio stage doesn't work well at all.

I wonder if regeneration could be implemented to simplify the
complicated filtering needed to produce clean output from QSD based
receiver?

I'm also wondering whether newer technology can automatically control
the regeneration as needed, which might give a technological boost to
an old concept and revive it in the process??!! It's happened before
(example is newer high performance phasing type receivers are much
easier to build with op amps and offer much higher performance in an
easier to build package).

I might try some regenerative feedback in some of the post detector
audio stages next time i have the radio on the bench.

Thanks,

Tra







On Sun, 30 Oct 2005 16:37:57 -0600, (Richard
Harrison) wrote:

TRABEM wrote:
"I didn`t price it yet, but I need more technical information!"

There`s a better approach than high "Q" capacitors for a VLF loop. It`s
been available since the year 1912 and much used soon after its
invention.

Edwin H. Armstrong, 1890 - 1964 was radio`s most productive inventor. He
invented regenerative control in 1912. I think he awakened his sister in
the middle of the middle of the night screaming : "Eureka, I`ve found
it!" or something to that effect. It wasn`t ubique for Howard Armstrong
to discover things. Following controlled regeneration, he discovered the
principle of the superhet in 1918, superregeneration in 1922, and the
complete system of frequency modulation in 1933. He would battle RCA and
Sarnoff for his entire life over control of his discoveries. I recall
seeing a photo of the battery portable radio Howard built and gave his
bride as a wedding present on an IEEE magazine cover.

Ever since 1912 there have been regenerative circuits introducing a
fraction of a receiver`s output back into its input to enhance its
amplification and sharpen its selectivity. Some of these are called "Q"
multipliers.

A "Q" multiplier is an oscillator circuit which has its regenerative
feedback adjusted just below the point of oscillation. It amplifies the
signal many times and shrinks the apparent bandwidth the tuned circuit
accepts. I`ve seen them used for reception of WWV at Boulder on 60 kHz
and for other low frequencies. This seems easier than using super parts.
Use some positive controlled feedback in the loop circuit. Adjust it for
convenience.

Best regards, Richard Harrison, KB5WZI

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Thanks John,

I'll have a look. The newest Antenna Handbook I have is a 1950
version::

I've never been terribly impressed with the Leagues Antenna Handbook.
If the antenna section in the newer Radio Amateurs Handbook is any
indication, I probably won't buy one either. But, I'll have a look
see. The Reference section at the college library has a copy, so I'll
swing by and have a look to see if it's worth buying.

Ain't technology wonderful??? It took me less than 60 seconds to
search all the college libraries in New England because all the
offerings are online now! And, as luck would have it, I found one
right down the street (figuratively speaking).

Thanks for the suggestion, I'll check it out.

Regards,

T



On Sun, 30 Oct 2005 09:41:17 -0500, "John N9JG"
wrote:

Take a look in the latest issue of the ARRL Antenna Book. Chapter 5 is
devoted entirely to loop antennas, and the chapter includes information
about small loops. At the end of the chapter is a nice sized bibliography.

TRABEM wrote in message ...
[stuff]

Getting back to last nights study session. Spent a couple of hours in
my 1987 ARRL Handbook and the remainder on the web looking at real
life loops published there. The web aspect was really disappointingly
devoid of technical jargon, it seems like most of the loop authors
just threw something up and it seemed to work-the end:: Do people
just throw stuff up without understanding what they're doing, or do
they understand and just fail to document the theory??

The Handbook tour was almost as bad. Very little was said about loops
except that which applied to the full wave resonant loop and how it
can serve as a driven element in a 1 lambda 'guad' type radiator.
Other than the theoretical wavelength, the correction factor for wire
diameter, there was not more than 2 paragraphs written with useful
information on short loops such as I am trying to put up.

[stuff]

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Sun, 30 Oct 2005 23:41:29 -0500, TRABEM wrote:
In general, no rf stage is needed (or desired).

In general, no rf stage has been designed into a receiver for a
quarter century. Hence touting it as a hallmark is rather pedestrian.

But, recovering the audio without DSP based software (usually
a sound card) is very difficult, needing large amounts of selective
audio filters slowly tailor the audio response to an appropriate
selectivity.

Even there, bi-quad active filters have been doing this for those same
25 - 30 years, and quite smartly too.

You need to return to basics a la Robert Pease who does a lot of
informational multimedia for National Semi these days. He properly
offers that so much that has been handed over to binary twiddling is
such a step backwards to accomplishing a job better handled in the
linear domain.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Sun, 30 Oct 2005 21:49:08 -0800, Richard Clark
Hi Richard,

In general, no rf stage is needed (or desired).

In general, no rf stage has been designed into a receiver for a
quarter century. Hence touting it as a hallmark is rather pedestrian.


True, but few of the inexpensive receivers that operate without rf
stages perform very well. And I don't know any commercial application
that uses regenerative feedback to gain selectivity in a real world
receiver application. Typically, receivers that perform well have many
(post detector) poles of modest Q filter stages to prevent undesirable
features such as ringing. This uses alot of hardware, especially
precision resistors and capacitors.

Yes, scaf filters are relatively clean, but it's still a multichip
solution needing quite a few R's and C's.

But, recovering the audio without DSP based software (usually
a sound card) is very difficult, needing large amounts of selective
audio filters slowly tailor the audio response to an appropriate
selectivity.

Even there, bi-quad active filters have been doing this for those same
25 - 30 years, and quite smartly too.

You need to return to basics a la Robert Pease who does a lot of
informational multimedia for National Semi these days. He properly
offers that so much that has been handed over to binary twiddling is
such a step backwards to accomplishing a job better handled in the
linear domain.


There's room for both. KK7P's single chip digital solution to
processing the I and Q from the detector to the speaker is quite
attractive. It offers the potential of high performance while freeing
us from the sound card/computer leash (and the big three Japanese
corportions that dominate the ham radio transceiver industry) that
currently restrains us. It's the missing link that makes high
performance digital solutions into a 'free standing' piece of
hardware.

It appears to me that DSP uses a great deal of power to do the job
though. In practical terms, what we save in portability and bulk with
a single chip digital solution might be minimal because we have to
carry bigger batteries to make it happen in a portable environment.

Like I said, there's room for both...and small changes in hardware
availability constantly move the equation regarding 'what's best for
me' in varying directions.

I prefer to know both digital and analog worlds though instead of
limiting myself by only knowing 1 possible option.

Since the original responder wrote about regenerative methods however,
I will keep my eye peeled for a practical means to implement it with
modern technology components. If it was implemented in the post
detector audio processing, it might minimize hardware needed to
achieve high selectivity with clean sounding audio. I thank him for
the reality check regarding this possibly useful method.

Regards,

T