Sharing one antenna among two transceivers?
 

I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

What would be great is if there was a switch that would share the line
between the 2 transceivers when no outgoing RF is present, and switch
everything to one rig when RF is sensed. However, I haven't seen a
product that does this!

thanks for any thoughts,

73,

Chuck
KB5GC

Hi Chuck

In the commercial world usually a circulator is used. It is in fact
quite common as the cost of setting up another tower sited antenna is
very high.

The big problem with sensing RF is that you are reacting to its
presence. Be better to run it from the PTT cct of the TX. I have seen
some build it yourself articles for high power PIN diode switches out
there. I dont have any URLs but the one I remember was on the LINRAD
site - or just do a google on "high power PIN".

Cheers Bob VK2YQA

Chuck W. wrote:
I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

On Fri, 01 Apr 2005 05:59:57 +1000, Bob Bob
wrote:

In the commercial world usually a circulator is used.

Hi Bob,

This would separate the two Transceivers, but they would both be deaf.

Circulators are used in frequency split repeaters where the transmit
path and receive path and frequency are different (and further loaded
with cavity filters).

73's
Richard Clark, KB7QHC

That is what DUPLEXERS are for! Tho, not to radios, on the same band.
they will allow one antenna (multiband) to be used by 2 , or 3 separate
radios at the same time! Comet, and couple other outfits make them.
(for vhf /uhf radios, some with an AM radio port for car radio).



Chuck W. wrote:
I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

What would be great is if there was a switch that would share the line
between the 2 transceivers when no outgoing RF is present, and switch
everything to one rig when RF is sensed. However, I haven't seen a
product that does this!

thanks for any thoughts,

73,

Chuck
KB5GC

"Chuck W." wrote in message
oups.com...
I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

What would be great is if there was a switch that would share the line
between the 2 transceivers when no outgoing RF is present, and switch
everything to one rig when RF is sensed. However, I haven't seen a
product that does this!



Is this for two transceivers on the same band or are they on differant bands
?

Ralph Mowery wrote:
Is this for two transceivers on the same band or are they on
differant bands
?

Might be the same, might be different. I was thinking about two HF
transceivers rather than VHF/UHF.

-Chuck

there is this thing called a "switch box"
two in one out
or one in two out

here is a pic of a three in/out
http://cgi.ebay.com/ws/eBayISAPI.dll...m=5762545 271
&tc=photo

I am not advertising, just a link to see one

Chuck W. wrote:
"I`m wondering what is the best practice for connecting two tranceivers
to a single transmission line / antenna,----?"

A "circulator" is the device to route the right energy to the right
destination among multiple input/output devices. It is composed of line
segments in multiples of 1/4-wavelength of transmission line or
waveguide. I made one of 600-ohm open-wire line to parallel two 50-KW
shortwave broadcast transmitters to one antenna and a dummy load in case
of upset. Both transmitters were excited from the same oscillator. It
worked well and there was no upset. I didn`t need the dummy load. The
circulator is sometimes called a "rat-race". In any case, I swear that
they work.

Microwave repeaters are often equipped with waveguide ferrite isolators
which allow energy to pass through in one direction with almost no loss
but which absorb rf power in the opposite direction. These make clever
use of "Faraday" rotation of the plane of polarization as the microwaves
travel through a ferrite slab lying in a magnetic field. These ferrite
sections allow the transmitter energy to reach the antenna but not reach
the associated receiver input of the repeater, so it won`t be
overloaded, desensesitized, or accept power which would be better spent
in reaching the next repeater.

With ferrite isolators, energy can be routed almost at will. I am still
embarrased when I recall dropping an isolator in Motorola`s Chicago
plant 45 years ago. The ferrite shattered like glass. They cost several
hundred dollars each at the time. The Motorolans graciously said to
think nothing of it, it happens all the time. Well I don`t drop valuable
stuf every day. If I did , no one would let me in! , unless I was going
to spend a few millions, which we did.

I think you can probably use a "rat-race".

Best regards, Richard Harrison, KB5WZI

On 31 Mar 2005 10:44:17 -0800, "Chuck W." wrote:

I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

What would be great is if there was a switch that would share the line
between the 2 transceivers when no outgoing RF is present, and switch
everything to one rig when RF is sensed. However, I haven't seen a
product that does this!

thanks for any thoughts,

73,

Chuck
KB5GC

MFJ used to make the 1700B -- it's been discontinued, but maybe you
can find one in remaining stock somewhere -- it handles up to 6
transceivers and 6 antennas, you can mix or match in any manner. It's
a manual switcher, tho', not automatic.

bob
k5qwg

I wouldn't trust an RF-sensed switch to do the job (have never seen one
anyway). The antenna jack on the rig that is NOT to be used would have to be
grounded first before allowing the primary rig to transmit. A bit of a
dilemma. You can use a manual coax switch (which grounds the unselected
outputs), but even then quite a bit of signal is coupled to the transceiver
who's connection is grounded. I tested this setup on HF, bringing the power
up slowly on the selected rig and tuning the unselected rig to the same
frequency. On 10 meters, the signal present on the unselected rig's input
was enough to cause a 45 dB over S9 signal. Not enough to damage the
frontend in this case, but you'd need to test the switch you're planning to
use to see what results you get.

K8AC


"Chuck W." wrote in message
oups.com...
I'm wondering what is the best practice for connecting two transceivers
to a single transmission line/antenna, or even if it is advisable to
do?

What would be great is if there was a switch that would share the line
between the 2 transceivers when no outgoing RF is present, and switch
everything to one rig when RF is sensed. However, I haven't seen a
product that does this!

thanks for any thoughts,

73,

Chuck
KB5GC

Floyd Sense wrote:
"I wouldn`t trust an RF-sensed switch to do the job (have never seen one
anyway)."

They abound. Plenty of devices are keyed when RF is sensed. Catastrophic
failure can be avoided by secondary protection for more security.

If simultaneous operation of two or more devices with one antenna is
required, switching between them wont work anyway. Some form of combiner
is needed.

A device for automatic switching is the duplexer used with RADAR which
automatically switches the antenna from receive to transmit at the
proper times.

A diplexer, on the other hand, is used to combine the picture and sound
transmitters to the same TV station antenna. This may be a bridge
circuit or something similar. Its purpose is to isolate the transmitters
from each other while feeding the same antenna.

That was also my goal in combining the outputs of two shortwave
broadcast transmitters to the same antenna but they were of the same
frequency and phase.

The circulator I suggested in an earlier posting is a variation on a
device described in a couple of books I used to have on amateur radio
repeaters. In my case I wanted to make a 100-KW transmitter from two
50-KW reansmitters. It worked well.

The medium-wave broadcast plant I worked in, with 950 KHz and 1320 KHz
transmitters, accessed the same tower through frequency pass / reject
filters in the coax lines to each transmitter from the same antenna. It
was no problem, given the frequency separation between the transmitters.
An amateur VHF repeater has a much more serious problem given a much
smaller percentage frequency separation between its receive and transmit
frequencies. The amateur repeater nust often use cavitiesto separate the
frequencies enough..

Best regards, Richard Harrison, KB5WZI

I wrote in a prior posting:
"The circulator I suggested in an earlier posting is a variation on a
device described in a couple of books I used to have on amateur radio
repeaters."

I still have not come across the repeater books but my 1987 ARRLHandbook
has such a circulator (called a hybrid ring) in Fig. 15 on page14-6, A
short escription is on the previous page. How it works is more
completely described in the repeater books.

Best regards, Richard Harrison, KB5WZI

Chuck W. wrote:

Ralph Mowery wrote:


Is this for two transceivers on the same band or are they on


differant bands


?



Might be the same, might be different. I was thinking about two HF
transceivers rather than VHF/UHF.

-Chuck



My rig, a Kenwood TS2000 has separate connections for the 2M and 70 cm
antennas, I use a duplexor to feed a dual band antenna., works great and
the duplexor was about $85 Cdn including shipping.

Paul