Lostgallifreyan wrote in
:

This is nice because it beats the issue with two ways to be selective.
Even so, I have to have one last shot at the broadband notion: could a
6dB boost with one of those MAR6-based antenna amps be worth a shot?
Driving a local diple, taped to a doorframe perhaps, in the centre of
the flat? Given the tiny size of those IC's I doubt the amount of power
getting out of the flat will be a nuisance, especially given its
reluctance to allow RF in (except through the celing, and a dipole taped
vertically to a doorframe isn't going to send a lot upwards either.. To
some extent the business may be eased by the fact that the two
frequencies I'm most keen to get, 91.5MHz and 93.7MHz, aren't far apart.
If there is ANY chance this can be solved with no modification or
encumbrance to the tiny radio I intend to carry from room to room,
that's the way I want to do it.


As a possible answer to my own question I can add this:

After looking on eBay to see if cheap widgets might be found and suitably
coerced, I learned that there are lots of cheal FM transmitters for immediate
local use, in nanowatt range for power. Following that up, I discover that in
the UK it is legal, as of around 2007, to set up such transmissions for car
and home use, and this is a starting point.

I know that if a dipole is cut from thicker stock, it is more broadband, has
less Q (and must be cut a tad shorter than theory states for an ideal wire).
I don't know a lot more than that, especially what results if two frequecies
fairly close to each other like 91.5MHz and 93.7MHz are.

Apart from objecting to UK govt policy on priciple (no bad thing right now,
as it happens..), is there any objection, thought, or advice anyone wants to
add to this? If it is an objection, I want a clear reasoning of why.

As far as I can tell so far, my original notion looks viable still, so long
as I can limit feedback and any emissions not directly matching signals
picked up in the first place, and so long as the total power is well within
the new legal requirements, which it will be, I want to use as little as
possible on the basis of feedback avoidance.

(In other news: that specific source of pulsed noise vanished, someone turned
it off nearly 48 hours ago, and it has not returned yet. The current problem
is purely one of attenuation, too little internal signal to allow clean
stereo sound on FM, and it looks like as little as 12dB would easily fix this
with no change to the way I use a portable radio.)

On 7/29/2014 2:23 PM, Lostgallifreyan wrote:
Lostgallifreyan wrote in
:

This is nice because it beats the issue with two ways to be selective.
Even so, I have to have one last shot at the broadband notion: could a
6dB boost with one of those MAR6-based antenna amps be worth a shot?
Driving a local diple, taped to a doorframe perhaps, in the centre of
the flat? Given the tiny size of those IC's I doubt the amount of power
getting out of the flat will be a nuisance, especially given its
reluctance to allow RF in (except through the celing, and a dipole taped
vertically to a doorframe isn't going to send a lot upwards either.. To
some extent the business may be eased by the fact that the two
frequencies I'm most keen to get, 91.5MHz and 93.7MHz, aren't far apart.
If there is ANY chance this can be solved with no modification or
encumbrance to the tiny radio I intend to carry from room to room,
that's the way I want to do it.


As a possible answer to my own question I can add this:

After looking on eBay to see if cheap widgets might be found and suitably
coerced, I learned that there are lots of cheal FM transmitters for immediate
local use, in nanowatt range for power. Following that up, I discover that in
the UK it is legal, as of around 2007, to set up such transmissions for car
and home use, and this is a starting point.



One of us is confused.
Do you want a FM transmitter or an amplifier.
The FM transmitter will transmit a frequency that your FM receiver will
receive, but you need to feed in a source of audio.


I know that if a dipole is cut from thicker stock, it is more broadband, has
less Q (and must be cut a tad shorter than theory states for an ideal wire).
I don't know a lot more than that, especially what results if two frequecies
fairly close to each other like 91.5MHz and 93.7MHz are.

You won't be able to notice any difference with any antenna you make
between 91.5 and 93.7 MHz. Just try to design it for the middle, you
probably won't hit it, but it will probably be close enough.


Apart from objecting to UK govt policy on priciple (no bad thing right now,
as it happens..), is there any objection, thought, or advice anyone wants to
add to this? If it is an objection, I want a clear reasoning of why.

As far as I can tell so far, my original notion looks viable still, so long
as I can limit feedback and any emissions not directly matching signals
picked up in the first place, and so long as the total power is well within
the new legal requirements, which it will be, I want to use as little as
possible on the basis of feedback avoidance.

(In other news: that specific source of pulsed noise vanished, someone turned
it off nearly 48 hours ago, and it has not returned yet. The current problem
is purely one of attenuation, too little internal signal to allow clean
stereo sound on FM, and it looks like as little as 12dB would easily fix this
with no change to the way I use a portable radio.)

amdx wrote in :

One of us is confused.
Do you want a FM transmitter or an amplifier.
The FM transmitter will transmit a frequency that your FM receiver will
receive, but you need to feed in a source of audio.


That could be you. Through several posts I mentioned enough detail to
cover all bases, but to summarise:

An antenna several tens of feet away is picking up good signals, but wired
connections to small portable radios often moved between rooms are
inconvenient (even dangerous obstacles if lying around in hallways, over
furniture, etc).

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? There's little doubt that it is very low power,
likely not able to send enough RF out to justifiably annoy anyone (especially
given the UK legal allowance of it now), and almost certainly not enough to
feed back to the external aerial given how much RF attenuation exists between
inside and outside as it is. Anyb excess can be reduced, this is not the
problem, the problem is getting enough in the first place.

So the question is: can the MAR-6 based aerial amp drive a dipole with a
similar power to that had from these new microtransmitters? It's going to see
a similar impedance for that intended, so whatever impediment there may be,
impedance doesn't seem likely to be a problem.

amdx wrote in :

You won't be able to notice any difference with any antenna you make
between 91.5 and 93.7 MHz. Just try to design it for the middle, you
probably won't hit it, but it will probably be close enough.


Ok. That's how I usually decide a dipole length anyway. (For receiving). What
I was unsure of is whether a tiny RF boost that was NOT a tuned circuit might
make the distiction important or useful in any way. (As it is, that amp I
once built has filters to limit it to UK FM broadcast band anyway).

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.

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...

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 7/29/2014 8:31 PM, Lostgallifreyan wrote:
amdx wrote in :

One of us is confused.
Do you want a FM transmitter or an amplifier.
The FM transmitter will transmit a frequency that your FM receiver will
receive, but you need to feed in a source of audio.


That could be you. Through several posts I mentioned enough detail to
cover all bases, but to summarize:


I understood what you are trying to do, but then you through in the FM
transmitter and I don't how that will help, unless you use it as
designed, but then to change channels you'll need to go to your audio
source and change the station.

Anyway, keep plugging away, as I listen to WABC in New York on my
internet radio, driving my FM transmitter that I receive on a portable
radio I carry around while doing my morning routine, part of which
is writing a compound sentence while in Florida. :-)
Mikek

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

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