On 7/29/2014 10:58 PM, Lostgallifreyan wrote:
Lostgallifreyan wrote in
:

A small FM aerial amplifier built around a MAR-6 IC works to boost the
signal for direct connection, but can it also be used to drive a
1/4-wave dipole for the immediate locality?

I found that old amp and a 1mH choke and 12VDC source so I tried it. The
answer is NO. Radiated power is so tiny that I think it would take a 5 grans
bit of test gear to analyse why in meaningful detail. I saw no difference
whether the power was on or off. The quickly-cobbled dipole itself was fine,
even as an indoor aerial wired directly to the input of an AR-3000 it was
excellent, nearly as good as outside, but it's the wires I want to avoid,
eventually.....

If I feel like trying again it will be with one of those legal
microtransmitters sometime, just the RF gain part, and probably with the
indoor radiating dipole horizontal to reduce coupling to the vertical one
outside.


The problem with what you're trying to do is you can easily get RF
feedback between the output antenna and the input antenna, causing
oscillations. And those oscillations may not be in the FM band - they
may be on an adjacent band (like aircraft, which is just above the FM band).

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in
:

The problem with what you're trying to do is you can easily get RF
feedback between the output antenna and the input antenna, causing
oscillations. And those oscillations may not be in the FM band - they
may be on an adjacent band (like aircraft, which is just above the FM
band).


That's my main concern, I want it to be well behaved, or it won't happen. It
has simple 1-pole LC filters to limit it to the FM broadcast band, but I will
leave it intact and not cobble it into another purpose because it's very good
at its original intent.

If I do experiment further, it looks like the best thing to watch out for is
any unexpected oscillation frequencies despite its filters (LPF on input, HPF
on output), and deliberately orienting a radiating dipole to minimise
feedback. Is it easy (or possible) to catch clues of such bad behaviour while
listeing using somethign like a Tecsun PL-390 or other radio using those new
DSP IC's? I ask that because they're cheap, easy to get, and fairly
consistent, and include a usefully specified signal strength meter. If so,
what should I consider to be a warnign sign?

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.


Agreed.
I only tried because the last thing I want to do is pollute the spectrum.
Start small...

On 7/30/2014 1:16 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in
:

The problem with what you're trying to do is you can easily get RF
feedback between the output antenna and the input antenna, causing
oscillations. And those oscillations may not be in the FM band - they
may be on an adjacent band (like aircraft, which is just above the FM
band).


That's my main concern, I want it to be well behaved, or it won't happen. It
has simple 1-pole LC filters to limit it to the FM broadcast band, but I will
leave it intact and not cobble it into another purpose because it's very good
at its original intent.

If I do experiment further, it looks like the best thing to watch out for is
any unexpected oscillation frequencies despite its filters (LPF on input, HPF
on output), and deliberately orienting a radiating dipole to minimise
feedback. Is it easy (or possible) to catch clues of such bad behaviour while
listeing using somethign like a Tecsun PL-390 or other radio using those new
DSP IC's? I ask that because they're cheap, easy to get, and fairly
consistent, and include a usefully specified signal strength meter. If so,
what should I consider to be a warnign sign?

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.


Agreed.
I only tried because the last thing I want to do is pollute the spectrum.
Start small...


1-pole LC filters won't be narrow enough to limit potential oscillations
to the FM band. You'll need much more than that.

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in news:lras98$ebf$1@dont-
email.me:

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.


No clues at all? I remember when I first set up that little MAR-6 based
preamp, it had some nasty side effects on the sound till I added a springy
ciopper alloy strip to each side on the underside of the board so it bit
gently into the aluminium case when I slid it in to it, finally curing the
local RF oscillations it had before I solved this. I was wondering if similar
audible sounds might be heard as a guide to other, larger scales of local
feedback and oscillation.

On 7/30/2014 5:00 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lras98$ebf$1@dont-
email.me:

As for determining whether it is oscillating or not - I wouldn't trust
anything short of a good spectrum analyzer. The signal could be
anywhere (and changing frequency). A spectrum analyzer will still show
it; a receiver won't necessarily.


No clues at all? I remember when I first set up that little MAR-6 based
preamp, it had some nasty side effects on the sound till I added a springy
ciopper alloy strip to each side on the underside of the board so it bit
gently into the aluminium case when I slid it in to it, finally curing the
local RF oscillations it had before I solved this. I was wondering if similar
audible sounds might be heard as a guide to other, larger scales of local
feedback and oscillation.


Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me:

Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.


Well, it was like a flanger having a psychedilc fit. Hard to ignore!
Fortunately easy to cure. I imagine that many other sources of wild RF
oscillation might affect the sound like that.

On 7/30/2014 5:08 PM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lrbmkt$ohq$1@dont-
email.me:

Not necessarily. Even if there were physical vibrations, they may be
out of the audible range. But even vibrations are not common. You were
lucky you could hear it.


Well, it was like a flanger having a psychedilc fit. Hard to ignore!
Fortunately easy to cure. I imagine that many other sources of wild RF
oscillation might affect the sound like that.


Not really. To affect the sound, you need something which will respond
to the RF in a physical vibration manner (i.e. magnetic), and the signal
must be in the audio spectrum.

Neither is very likely.

--
==================
Remove the "x" from my email address
Jerry Stuckle

==================

Jerry Stuckle wrote in news:lr9ohj$33f$1@dont-
email.me:

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.


Small point, but.... Microwatts. Those new legal microstransmitters are said
to be in NANOwatt range output, but allegedly work on the distance scales I'm
interested in. Microwatts should certainly have worked, but despite the crude
test dipole being good (on standard wired reception test anyway), it didn't
work for transmitting even a foot or two with the radio's whip parallel to
the upper part of it. If nanowatts should have, the MAR-6 looks like driving
picowatts, if I'm lucky.

On 7/30/2014 1:22 AM, Lostgallifreyan wrote:
Jerry Stuckle wrote in news:lr9ohj$33f$1@dont-
email.me:

But the amplifier you're trying to use is meant to feed a receiver
directly, not another antenna. So output is going to be very low (on
the order of microwatts) - much lower than any amplifier which feeds an
antenna.


Small point, but.... Microwatts. Those new legal microstransmitters are said
to be in NANOwatt range output, but allegedly work on the distance scales I'm
interested in. Microwatts should certainly have worked, but despite the crude
test dipole being good (on standard wired reception test anyway), it didn't
work for transmitting even a foot or two with the radio's whip parallel to
the upper part of it. If nanowatts should have, the MAR-6 looks like driving
picowatts, if I'm lucky.


I would suggest you check again. Receivers aren't that sensitive. Most
unlicensed transmitters are in the 100-500 mw range, and have a coverage
of maybe 100 feet. And picowatts aren't even worth discussing.

--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

Jerry Stuckle wrote in news:lraskh$gup$1@dont-
email.me:

Most
unlicensed transmitters are in the 100-500 mw range, and have a coverage
of maybe 100 feet.

That sounds right. I thought nanowatts seemed a bit small a claim. I probably
need about 10mW based on what you said there. (I think it was Wikipedia's
article that stated the nanowatts, but as so often happens, there was no
mention of the antenna and actual radiated power, no hint of what efficiency
(or lack of) resulted.

I won't retry for now. Messing around with a direct wired link to the
external aerial is more fun for a while. ETM on a PL-390 is as fun as many
people have said it is...


And picowatts aren't even worth discussing.


I should never have mentioned them.