On 7/26/2014 12:32 AM, Jeff Liebermann wrote:
On Fri, 25 Jul 2014 14:21:07 -0500, Lostgallifreyan
wrote:

I hope to boost the incoming signal to override the ocal RF mush from nearby
flats, and to do this for a portable receiver so I want no cables attached to
it at all. I have considered two possible ideas:

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



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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.

http://www.m0ukd.com/wordpress/homebrew/magnetic-loop-antennas/
He forgot to insert a series tuning cap in the gamma match, but
otherwise, it should give you an idea of what's involved.

http://www.iw5edi.com/technical-articles/144-mhz-magnetic-loop-antenna
Much better.

Anyway, recalculate for 100 MHz and it should work.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

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


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amdx wrote in :

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.


Slightly cubersome for my situaion but technically true, so a nice idea.
Thanks.

On 7/26/2014 1:19 PM, Lostgallifreyan wrote:
amdx wrote in :

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.


Slightly cumbersome for my situation but technically true, so a nice idea.
Thanks.

Ya, I'm thinking a 3 or 4 turn loop to fit the back of the radio.
I had to work all day, earlier I had thoughts about putting one my GE
Suoerradio III just to see if it works. A spiral form may be less
cumbersome. I have a bunch of ten pf caps, but I haven't calculated
anything yet so don't know if 2pf to 10pf would resonate with a
reasonable size coil.
Mikek

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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