On Mar 20, 12:58 pm, Artem wrote:
On Mar 15, 12:28 am, K7ITM wrote: On Mar 14, 2:15 pm, Artem wrote:

Yes...very good. That should help keep the loop nicely balanced,

especially if you build it all very symmetrical. That one more tube

Hi. I have some problem. I can't receive nothing except noise And self
oscillation frequency.
I have some photos. Could any give me some suggestions?
Antenna:http://artembond.no-ip.info/apache2-...t/DSC_9427.JPG

Chematics:http://artembond.no-ip.info/apache2-...t/DSC_9431.JPG

Amplifier:http://artembond.no-ip.info/apache2-...t/DSC_9426.JPG

:-) I saw the comment about "narrow-banding" the images. They were
perhaps a little more than we needed, but it was nice to have
something we could actually see. They did not take very long to
download here, but someone with a slow connection may have troubles.

One comment: usually you do not need much voltage gain. It is enough
to get power gain with the FETs. That is, the received signal voltage
across the gap of the loop, as resonated by the capacitors, should be
high enough to be used with a good receiver. The problem is that the
impedance is very high there. But that same high impedance makes for
easy oscillation. From what you posted, it sounds like maybe you have
identified an oscillation. If the AGC voltage is low enough, does the
oscillation stop? The amplifier I built used two stages, an FET input
stage and a buffer stage, and it had very low voltage gain--I am
remembering about 3:1 or only 10dB, and maybe only 1:1 or 0dB
including the output transformer, but quite a bit of power gain since
it transformed the high loop impedance down to 50 ohms for the
feedline.

Also, there should be no need for the RF chokes from the gate-1 to
source, if the loop is grounded at the bottom. If the loop is
grounded at the bottom, the loop plus the RF chokes will short out the
source-to-ground resistor. Maybe there is not a need to raise the
source voltage above DC ground potential anyway. Also, it may help to
NOT bypass the sources to ground, to allow some negative feedback.
That may help stabilize the amplifier.

If other things occur to me, I will post them...

Cheers,
Tom