On Mar 21, 10:02 am, Artem wrote:
On Mar 21, 6:26 pm, K7ITM wrote:

On Mar 21, 3:08 am, Artem wrote:

Sources is not grounded.

Yes, unfortunately noise that is generated more than one or two
wavelengths away from your antenna will be almost entirely
electromagnetic by the time it reaches your antenna. Antennas do not
differentiate between "electrically generated" and "magnetically
generated" noise, when you are far enough that the electromagnetic

I did not hear nothing about electrically or magnetically photons.
It's just photons.

:-) Oh, no, not photons again! When you are near to a source -- to a
transmitting antenna or to a computer radiating noise -- the fields in
general have not developed fully into electromagnetic waves -- photons
if you wish. It is quite usual that, close to the source, either the
electric or the magnetic field will dominate. Often from noise
sources, the near field is predominantly electric, and a properly done
loop antenna will reject that, responding only to the, um, photons.

field dominates over any near-field electric or magnetic field. The
balanced small loop is good for rejecting electric-field noise only if
(1) the noise is generated close to the antenna and

Yes. Computer, lamps etc close to antenna.

(2) the antenna is
close to the ground (so the electric field is guaranteed to be nearly

15 floor of 16-floor building. But I think that in this case "ground"
are building walls.

There is a hint he it is common that tall buildings incorporate a
lot of steel, and that will likely act as a shield. I hope this
antenna is not mounted inside!

vertical) -- -- where "close" means relative to a wavelength. So the
small balanced loop is especially good for LF and VLF work.

my reason was make narrow-band antenna. For reject all out of band
noise.

A reasonable thing to do, though a good receiver with a low-distortion
and fairly narrow-band front end should not have trouble with out-of-
band signals (noise). Do you have a quantitative measure of just how
strong this out of band noise is? I'd personally much rather use a
preselection filter separate from the antenna, and close to my
operating position, to reject out-of-band signals. Even though the
antenna you have described has very high Q, I believe I could do
better with a two or three resonator filter running at lower Q, since
the slope of the attenuation versus frequency is much greater. Unless
there was some especially strong signal in the band, I would at least
consider a fixed-tuned bandpass filter that covered my band of
interest, assuming that band is fairly narrow such as 7.0-7.1MHz.

Can you tell that you are getting the expected antenna bandwidth,
about 3kHz at the 3dB points at 7MHz?

If the amplifier at the antenna has a tendency to oscillate, it very
likely also has poor intermodulation performance. Be careful that it
doesn't destroy the benefits you are trying to obtain.

Cheers,
Tom

On Mar 22, 8:48 pm, K7ITM wrote:


15 floor of 16-floor building. But I think that in this case "ground"
are building walls.

There is a hint he it is common that tall buildings incorporate a
lot of steel, and that will likely act as a shield. I hope this
antenna is not mounted inside!

It's not mounted at all. But for tests I'm put this antenna outside.




vertical) -- -- where "close" means relative to a wavelength. So the
small balanced loop is especially good for LF and VLF work.

my reason was make narrow-band antenna. For reject all out of band
noise.

A reasonable thing to do, though a good receiver with a low-distortion
and fairly narrow-band front end should not have trouble with out-of-
band signals (noise). Do you have a quantitative measure of just how
strong this out of band noise is?
Not. Just not received.

I'd personally much rather use a
preselection filter separate from the antenna, and close to my
operating position, to reject out-of-band signals. Even though the
antenna you have described has very high Q, I believe I could do
better with a two or three resonator filter running at lower Q, since
the slope of the attenuation versus frequency is much greater.

I will receive QRSS at all. And I think that it would be best way is
using
narrow-band antenna - filter - synchronous detector.

there was some especially strong signal in the band, I would at least
consider a fixed-tuned bandpass filter that covered my band of
interest, assuming that band is fairly narrow such as 7.0-7.1MHz.

Can you tell that you are getting the expected antenna bandwidth,
about 3kHz at the 3dB points at 7MHz?

I'm just testing. I will purchase RF generator in next week and test.
Now I have only self-oscillation frequency.

Antenna looks like working. I'm receiving a lots of Morse signals at
7.000 - 7050 Mhz. But I cant recognize any voice signal.

This is receiving signal. Looks like narrow-band enough. This is not
self oscillation. In self oscillation voltage a few volts.
http://img148.imageshack.us/my.php?image=ds0000bu6.png

This is schematics. I'm not sure that I'm correct use gual gate
transistors.
http://img210.imageshack.us/my.php?image=schbr1.jpg

I'm not sure that using shielded cable and ferrite chocks is good
idea.
http://img171.imageshack.us/my.php?image=hwak2.jpg

np0 caps.
http://img370.imageshack.us/my.php?image=capsnf8.jpg

COOL! All worked!

On Mar 23, 11:48 pm, Richard Clark wrote:
On Sun, 23 Mar 2008 12:39:35 -0700 (PDT), Artem
wrote:

Antenna looks like working. I'm receiving a lots of Morse signals at
7.000 - 7050 Mhz. But I cant recognize any voice signal.

Side Band?

No. Out of band. I'm now add varicaps and all working! Antenna really
very narrow.


I'm not sure that using shielded cable and ferrite chocks is good
idea.

Not enough choking and needs to be repeated a quarter wave down the
choked wire(s).

It's 7Mhz. quarter wave is 10 miters.

I'm use choking:
between amplifier and antenna
between transformer and coax cable.
For amplifier power wires and gain control.

On Sun, 23 Mar 2008 12:39:35 -0700 (PDT), Artem
wrote:

Antenna looks like working. I'm receiving a lots of Morse signals at
7.000 - 7050 Mhz. But I cant recognize any voice signal.

Side Band?

I'm not sure that using shielded cable and ferrite chocks is good
idea.

Not enough choking and needs to be repeated a quarter wave down the
choked wire(s).

73's
Richard Clark, KB7QHC

On Sun, 23 Mar 2008 14:42:22 -0700 (PDT), Artem
wrote:

I'm not sure that using shielded cable and ferrite chocks is good
idea.

Not enough choking and needs to be repeated a quarter wave down the
choked wire(s).

It's 7Mhz. quarter wave is 10 miters.

Then again at the far end of the wire(s).

I'm use choking:
between amplifier and antenna
between transformer and coax cable.
For amplifier power wires and gain control.

I've observed that, and I have observed it is not enough from your
photo - if you still have self-oscillation. Your pictures do not
reveal any choking of the RF Out cable.

As for the diagonal arm for "ground." This is fine insofar as it
being placed in the electrical middle of the antenna loop (a ground),
but all this rat's nest of wiring throws the concept of balance out
the window. I see in earlier pictures where you clean that up with
careful routing, but it seems much too busy. This leads me into the
comments following:

On another note, the AGC seems overly elaborate, especially when all
that wire could be introducing the self-oscillation. Further, wiring
in power seems another invitation to problems when a 9V battery would
solve that too. Local power would discard the need for the ground
coming from the loop's perimeter, eliminate unnecessary AGC, reduce
the complexity of choking, lower gain (it obviously has too much), and
give you only one coax coming from the antenna.

You need to solve the self-oscillation through removing complexity.
When you accomplish that, THEN that is the time to add it back in, one
thing at a time. You will probably discover all those features and
design gimmicks are not worth it.

73's
Richard Clark, KB7QHC

On Sun, 23 Mar 2008 14:27:49 -0700 (PDT), Artem
wrote:

COOL! All worked!

It would seem no further advice is necessary, much less my last bit of
wisdom on the topic.

It would help if you were to elaborate as to what actually killed the
oscillation.

73's
Richard Clark, KB7QHC

On Mar 24, 3:24 am, Richard Clark wrote:
On Sun, 23 Mar 2008 14:42:22 -0700 (PDT), Artem
wrote:

I'm not sure that using shielded cable and ferrite chocks is good
idea.

Not enough choking and needs to be repeated a quarter wave down the
choked wire(s).

It's 7Mhz. quarter wave is 10 miters.

Then again at the far end of the wire(s).

I'm use choking:
between amplifier and antenna
between transformer and coax cable.
For amplifier power wires and gain control.

I've observed that, and I have observed it is not enough from your
photo - if you still have self-oscillation. Your pictures do not
reveal any choking of the RF Out cable.

It's inside. Nearby BNC socket.


As for the diagonal arm for "ground." This is fine insofar as it
being placed in the electrical middle of the antenna loop (a ground),
but all this rat's nest of wiring throws the concept of balance out
the window.

I think that some disbalance should compensate differencial amplifier
on transistors.

I see in earlier pictures where you clean that up with
careful routing, but it seems much too busy. This leads me into the
comments following:

On another note, the AGC seems overly elaborate, especially when all
that wire could be introducing the self-oscillation. Further, wiring
in power seems another invitation to problems when a 9V battery would
solve that too. Local power would discard the need for the ground

Yes. But FETs draw more that 10ma each.

coming from the loop's perimeter, eliminate unnecessary AGC, reduce
the complexity of choking, lower gain (it obviously has too much), and
give you only one coax coming from the antenna.

Cable length is not problem. I'm living in apartment. I can put
antenna outside the window. But not on the roof.

I can make power supply over coax cable. I can put Atmega8 (en
example) to amplifier and add DACs for operate varicaps, AGC. I can
add rectifier and filter for detect self-oscillation and automatics
reduce AGC. But it's not necessary.

On Mar 24, 5:45 pm, Richard Clark wrote:
As for the diagonal arm for "ground." This is fine insofar as it
being placed in the electrical middle of the antenna loop (a ground),
but all this rat's nest of wiring throws the concept of balance out
the window.

I think that some disbalance should compensate differencial amplifier
on transistors.

That makes no sense whatever.

Disbalance mean in-phase signal on gate 1 FETs. differencial will not
amplify this signal.

Sounds like a lot of unnecessary complexity. The one thing you repeat
is varicaps, but I don't see them.

I have. I just did now how them because this is trivial.

On Mar 24, 5:45 pm, Richard Clark wrote:
As for the diagonal arm for "ground." This is fine insofar as it
being placed in the electrical middle of the antenna loop (a ground),
but all this rat's nest of wiring throws the concept of balance out
the window.

I think that some disbalance should compensate differencial amplifier
on transistors.

That makes no sense whatever.

Disbalance mean in-phase signal on gate 1 FETs. differencial will not
amplify this signal.

Sounds like a lot of unnecessary complexity. The one thing you repeat
is varicaps, but I don't see them.

I have. I just did now how them because this is trivial.