One antenna, multiple receivers?
 

Okay, this may be a newbie-type question - or even an exercise in
academics - but since I'm about to find myself with more than one receiver
for the first time in a long time, I'd like to ask the group the following:

Assume I am limited to a single simple antenna (for the sake of this initial
discussion, let's not assume that I can have a particular type of antenna;
just that I can have only one) and have more than one receiver.

Questions arising:

1) Is it *possible* to connect multiple receivers to a single antenna?

2) Does is require the use of some sort of isolation circuitry for each
receiver's feed? If so, what kind?

3) Can I then attach multiple antenna tuners to that single antenna and
optimize each receiver's feed?

4) Would I be better off to try to disguise several seperate antennas as
a single antenna - e.g. several long wires bundled together as one - or
would that cause other problems on the receivers' front ends?

Thanks!

"digitania" wrote

1) Is it *possible* to connect multiple receivers to a single antenna?

2) Does is require the use of some sort of isolation circuitry for
each
receiver's feed? If so, what kind?

3) Can I then attach multiple antenna tuners to that single antenna
and
optimize each receiver's feed?

4) Would I be better off to try to disguise several seperate antennas
as
a single antenna - e.g. several long wires bundled together as one - or
would that cause other problems on the receivers' front ends?

A passive or active multicoupler is just what you want. These devices
electrically isolate each output (typically either 2 or 4 ouputs provided).
The passive versions have between 2-4 db insertion loss. The active versions
boost the signal so the loss is overcome (and then some). Active
multicouplers require a 12vdc power supply to them, usually about 200-300
milliamps.

Each output of a multicoupler could have an antenna tuner attached to it.
However, it is likely that trying to tune an antenna out of it's bandwidth
could result in unacceptable draw-down of available signal strength for
other receivers. This is even with an active multicoupler, which are the
only kind acceptable for any kind of DX-type work. Multicouplers are great
tools, but they have their limits! They are also prone to amplifying local
intermod (pager towers etc) when used in UHF bands. You have to choose the
bandwidth-type you require, and two major manufacturers below are well
known:

Stridsberg (very expensive) ~ $150, and
Industrial Communication Engineers (ICE), ~ $50.

Receivers don't care what form of input you give them, but by receivers we
do not mean portables. Most portable radios are miserable performers when a
high gain signal from an external antenna is connected to them. They are
made to do their best job with the provided whip or 12' or so of
inside-the-home external wire only. If you want to add several receive
antennas in parallel to each other that's not a bad idea either. But
bundling them together would be counterproductive, and a detriment to each
of their capabilities.

If you wanted to receive HF/SSB, SW, AM broadcast, VHF and UHF in one
antenna, I would suggest a discone, scantenna-type antenna. Even though
these usually advertise 25-1300 mhz reception, most of us have tried them
even on low-band SSB with pretty surprising results. Otherwise the wire
antenna will be the best bet for HF/SSB, shortwave and AM broadcast only.
Even your rain gutters can funtion in this capacity. Some enterprising hams
have even transmited through rain gutters, lol.

Hope this helps,

Jack
Virginia Beach

"Telamon" wrote
"digitania" wrote:

3) Can I then attach multiple antenna tuners to that single antenna
and
optimize each receiver's feed?

No. Most receivers have the same input impedance - about 50 ohms so you
would only need one tuner. The tuner resonates the antenna at some
frequency of interest.
--
Telamon
Ventura, California

Sorry there buddy, you are mistaken in that comment about resonating an
antenna. Tuners don't "resonate" anything, they simply fool a transmitter
into thinking it has a good impedance match. This is done between the tuner
and the transmitter only, even if ridiculous impedance and reactance
actually exists on several parts of the feedline and/or antenna. In that
case, the tuner will have to dissipate a lot of heat that the antenna system
throws back at it. When a receiver is connected to a tuner, the tuner
likewise simply balances the piece of line between itself and the receiver
and nothing else. This often improves reception, but it has no affect on the
antenna whatsoever.

Jack
Virginia Beach VA

patgkz wrote:

I used a simple "power devider" made of resistors. I just attached several
100 ohm resistors to the center conductor of my antenna lead-in, then ran
separate coax's, fanned out from the resistors, to the other receivers. You
lose about 6dB of signal to each radio....a small price to pay for the
convenience of hooking half a dozen radio's to one antenna. Cheap to do,
too.

I suppose it all depends upon what one is intent upon hearing. 6 dB is pretty
much equivalent to 1 S unit.

Personally, if I can avoid it, I'd rather not give up the 1 S unit.

dxAce
Michigan
USA

"Jack Painter" wrote in message
news:N6Urd.1972$Ro.742@lakeread02...

"Telamon" wrote
"digitania" wrote:

3) Can I then attach multiple antenna tuners to that single
antenna
and
optimize each receiver's feed?

No. Most receivers have the same input impedance - about 50 ohms so you
would only need one tuner. The tuner resonates the antenna at some
frequency of interest.
--
Telamon
Ventura, California

Sorry there buddy, you are mistaken in that comment about resonating an
antenna. Tuners don't "resonate" anything, they simply fool a transmitter
into thinking it has a good impedance match. This is done between the
tuner
and the transmitter only, even if ridiculous impedance and reactance
actually exists on several parts of the feedline and/or antenna. In that
case, the tuner will have to dissipate a lot of heat that the antenna
system
throws back at it. When a receiver is connected to a tuner, the tuner
likewise simply balances the piece of line between itself and the receiver
and nothing else. This often improves reception, but it has no affect on
the
antenna whatsoever.

Jack
Virginia Beach VA


Durn it, you mean that remote tuner out in my backyard at the antenna is
just fooling my transmitter/receiver?

I think you are talking about a transmatch, commonly and mistakenly called
an antenna tuner - which has nothing to do with an antenna and, as you say,
tunes nothing.

Dave

In article N6Urd.1972$Ro.742@lakeread02,
"Jack Painter" wrote:

"Telamon" wrote
"digitania" wrote:

3) Can I then attach multiple antenna tuners to that single
antenna and optimize each receiver's feed?

No. Most receivers have the same input impedance - about 50 ohms so you
would only need one tuner. The tuner resonates the antenna at some
frequency of interest.
--
Telamon
Ventura, California

Sorry there buddy, you are mistaken in that comment about resonating an
antenna. Tuners don't "resonate" anything, they simply fool a transmitter
into thinking it has a good impedance match. This is done between the tuner
and the transmitter only, even if ridiculous impedance and reactance
actually exists on several parts of the feedline and/or antenna. In that
case, the tuner will have to dissipate a lot of heat that the antenna system
throws back at it. When a receiver is connected to a tuner, the tuner
likewise simply balances the piece of line between itself and the receiver
and nothing else. This often improves reception, but it has no affect on the
antenna whatsoever.

Sorry to give you and maybe other people the wrong impression but that
is the problem with definitions. A tuner resides between the antenna and
the transmission line to the radio. The tuner has reactive components
that together with the antenna element form a resonate circuit which
will resonate at some frequency. The tuner design will depend on the
antenna type and could be as simple as a capacitor reacting with the
antenna element inductance.

If you are a ham you might have thought I was referring to an impedance
matching unit which prevents a transmitter from seeing an unmatched load
with the resultant SWR.

Or you might have thought I was referring to a high-pass, low-pass or
bandpass filter some people use for SWL'ing but no, I was referring to
a unit that actually resonates the antenna which was an answer to one of
the original posters questions if I understood him correctly.

--
Telamon
Ventura, California

Telamon schrieb:


If you are a ham you might have thought I was referring to an impedance
matching unit which prevents a transmitter from seeing an unmatched load
with the resultant SWR.

Or you might have thought I was referring to a high-pass, low-pass or
bandpass filter some people use for SWL'ing but no, I was referring to
a unit that actually resonates the antenna which was an answer to one of
the original posters questions if I understood him correctly.


It's prety much the same. It only depends of the length aka the loss of
the cable between the "matching unit" and the antenna.
It doesn't make much difference on relatively low freqs (HF) using a low
loss cable and using the "matching unit" in the shack or outside on the
feeding point.