On 7/26/2014 10:57 AM, amdx wrote:
On 7/26/2014 10:15 AM, Jeff Liebermann wrote:
On Sat, 26 Jul 2014 09:22:08 -0500, amdx wrote:
Hey Jeff,
Is it possible to build a tuned loop connected to the backside of the
radio, to cover the FM band. I never tried a loop at 100Mhz.
Mikek

Sure. Google for VHF magnetic loop antenna.
https://www.google.com/search?q=vhf+magnetic+loop+antenna&tbm=isch
They work so-so, but have the same problem as the HF version. The Q
is very high resulting in extremely narrow usable bandwidth. In order
to make it work, there would need to be some way of tuning the loop to
frequency. Making it track the receiver frequency would be a big
plus.

I expected to have a tuning cap on the loop to tune to his frequency
of interest. I don't know about polarization, but he may be able to
rotate out some interference with a loop.


Mikek


I've* calculated a 6 inch loop made with a #12 or #14 wire will
resonate the FM band with a cap between 6.5pf and 10pf. Roughly!
Now, I'll see if I can generate the gumption in the next couple
of days to build it to see if it has any positive effect.
I hope someone beats me to it.
With an AM loop and radio the signal couples to the internal loop very
well, I don't know how well you can couple a signal into an FM radio.
Mikek

* actually I used a couple of online calculators.

http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml

amdx wrote in :

I've* calculated a 6 inch loop made with a #12 or #14 wire will
resonate the FM band with a cap between 6.5pf and 10pf. Roughly!
Now, I'll see if I can generate the gumption in the next couple
of days to build it to see if it has any positive effect.
I hope someone beats me to it.
With an AM loop and radio the signal couples to the internal loop very
well, I don't know how well you can couple a signal into an FM radio.
Mikek

* actually I used a couple of online calculators.

http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml


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.

On 7/26/2014 10:51 PM, Lostgallifreyan wrote:
amdx wrote in :

I've* calculated a 6 inch loop made with a #12 or #14 wire will
resonate the FM band with a cap between 6.5pf and 10pf. Roughly!
Now, I'll see if I can generate the gumption in the next couple
of days to build it to see if it has any positive effect.
I hope someone beats me to it.
With an AM loop and radio the signal couples to the internal loop very
well, I don't know how well you can couple a signal into an FM radio.
Mikek

* actually I used a couple of online calculators.

http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml


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.

I made a 6 inch loop with a 2pf to 10pf cap, I could see a peak in
the loop where I adjusted it to, but it was very low Q and when I
started dangling it around my radio I couldn't hear any change.
It may take a slightly smaller loop, I had my cap set at minimum
to get it to tune the low end of the band.
In my mind the experiment failed.
I have had loads of fun with AM band loops with high Q and obvious
effect on reception.
Mikek

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amdx wrote in :

I made a 6 inch loop with a 2pf to 10pf cap, I could see a peak in
the loop where I adjusted it to, but it was very low Q and when I
started dangling it around my radio I couldn't hear any change.
It may take a slightly smaller loop, I had my cap set at minimum
to get it to tune the low end of the band.
In my mind the experiment failed.
I have had loads of fun with AM band loops with high Q and obvious
effect on reception.


Thanks for trying though, it's good info. One reason I imagined staying with
a dipole is it's close to what already works as standard. A loop for VHF is a
niuce idea for the selectivity of tuning and of orientation, but most radios
couple VHF to what amounts to a wire, not a magnetic coupling, so my
suspicion is that aiming for magnetic coupling won't work so well as a
dipole.

On 7/27/2014 3:16 PM, amdx wrote:
On 7/26/2014 10:51 PM, Lostgallifreyan wrote:
amdx wrote in :

I've* calculated a 6 inch loop made with a #12 or #14 wire will
resonate the FM band with a cap between 6.5pf and 10pf. Roughly!
Now, I'll see if I can generate the gumption in the next couple
of days to build it to see if it has any positive effect.
I hope someone beats me to it.
With an AM loop and radio the signal couples to the internal loop
very
well, I don't know how well you can couple a signal into an FM radio.
Mikek

* actually I used a couple of online calculators.

http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml


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.

I made a 6 inch loop with a 2pf to 10pf cap, I could see a peak in
the loop where I adjusted it to, but it was very low Q and when I
started dangling it around my radio I couldn't hear any change.
It may take a slightly smaller loop, I had my cap set at minimum
to get it to tune the low end of the band.
In my mind the experiment failed.
I have had loads of fun with AM band loops with high Q and obvious
effect on reception.
Mikek

Hi, Mike - 6 inch circumference, 6 inch diameter, or 6 inch radius. Just
clarifying...

John

On 7/27/2014 4:35 PM, John S wrote:
On 7/27/2014 3:16 PM, amdx wrote:
On 7/26/2014 10:51 PM, Lostgallifreyan wrote:
amdx wrote in :

I've* calculated a 6 inch loop made with a #12 or #14 wire will
resonate the FM band with a cap between 6.5pf and 10pf. Roughly!
Now, I'll see if I can generate the gumption in the next couple
of days to build it to see if it has any positive effect.
I hope someone beats me to it.
With an AM loop and radio the signal couples to the internal loop
very
well, I don't know how well you can couple a signal into an FM radio.
Mikek

* actually I used a couple of online calculators.

http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml



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.

I made a 6 inch loop with a 2pf to 10pf cap, I could see a peak in
the loop where I adjusted it to, but it was very low Q and when I
started dangling it around my radio I couldn't hear any change.
It may take a slightly smaller loop, I had my cap set at minimum
to get it to tune the low end of the band.
In my mind the experiment failed.
I have had loads of fun with AM band loops with high Q and obvious
effect on reception.
Mikek

Hi, Mike - 6 inch circumference, 6 inch diameter, or 6 inch radius. Just
clarifying...

John

Diameter.

Five minutes with these calculators and you can pick your own dimensions.


http://www.deephaven.co.uk/lc.html

http://www.daycounter.com/Calculator...lculator.phtml

Mikek

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This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

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.

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.