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:
I've actually done something like that for a customer, but first, I'll
take apart you two possible ideas;
1. Take a feed from my existing outdoor antenna and make a dipole indoors,
for passive re-radiation of whatever the outdoor one picks up.
Passive repeaters do not work well. I can go through the calculations
for you but basically, you get approximately twice the path loss with
a passive repeater, as you would with a direct path. I can grind the
numbers for you if you want later (I'm giving a talk tomorrow and need
to get some sleep).
2. Same thing, but using a small preamp I built once (uses a MAR6 I think,
about 22dB gain), but instead of feeding the RF input on a tuner as usual,
drive a small dipole to allow any small receiver with a whip or a wire to get
enough of the externally derived signal to beat the indoor mush.
What is there to keep the amplifier from amplifying the "mush"? If
you point your directional antenna in the wrong direction, you just as
easily be pointing it at the source of the noise. However, that's a
minor problem compared to multipath. You will still have some signal
arriving directly from the FM station, which will combine in some
random fashion with the amplified signal. If the phase difference
between the incident and amplified paths is 180 degrees, you'll have a
null and no signal. At 100 Mhz, 1/2 wave is about 1.5 meters, so
you'll have nulls every 1.5 meters inside your house.
(I think that feedback would be a problem, with any serious power, but
perhaps something as small as the MAR6-based booster I mentioned might work
ok, given that the outdoor antenna is several tens of feet distant.
Yes, it will be a problem. If you want to do that, read about how the
various cell phone bi-directional amplifiers prevent feedback.
(warning: It's messy).
Anyway,
that's the idea, and if it, or something I haven't thought of or mentioned at
all will solve this for me, please tell me. Alternatively, please tell me
what is the impossible obstacle to this notion...)
David Platt had the right idea. Build a repeater. You start with a
quality FM receiver that has a coax connector for the antenna.
Hopefully, it would get good reception and not pickup as much noise.
The audio output of the FM receiver would drive a Bluetooth wireless
speaker arrangement. Trade your portable receiver for a pair of BT
earphones or maybe a smartphone with BT. I suggest you go with the
newer BT 4.0 (BT Low Energy) instead of the older BT 3.0 (BT
standard). Range is about 10-30 meters, which should be adequate.
Something like this:
http://www.ebay.com/itm/311024899511
Search for: Bluetooth audio transmitter.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558