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another antenna question


Mark Lewin
 

I have a question like Randy's but just the opposite situation.
I have one scanner but two antennas (both indoor).

I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high bands.  I have one antenna that is especially good at the 800 band and another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.  I use a BNC T-connector to mount both antennas at the same time. I get significant loss on the 800 MHz band when I do this.  I might get loss on the other bands from the other antenna also, but have not tested that scenario yet.

My question is where does this loss come from?  Is it the proximity of the two antennas from one another (they are right next to each other only a few inches apart). Or is it from the T connector itself?   Asked in a different way, if I used a jumper cable off the T so the two antennas were separated by 6 feet of more, would I see a benefit or (if the T connector is the problem) would there be no difference?




Joe M.
 

You want to use a device called a Diplexer to connect multiple antennas.
(that would be the 'best' equivalent of the previous case)

Your second antenna may be providing a 'short' of the 800 MHz signals.

I'm trying to think of a good analogy. Let's say you have a garden hose with a splitter. Ideally, that would provide equal splitting to the two hoses, but when one hose is larger it will such the water and leave the smaller hose with little. Not the greatest example, but...

Google "RF shorting stub" and you will see. Your second antenna may effectively be a shorted stub for 800 MHz signals and is nulling them.

Joe M.

On 1/12/2021 3:19 PM, Mark Lewin wrote:
I have a question like Randy's but just the opposite situation.
I have one scanner but two antennas (both indoor).

I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high
bands. I have one antenna that is especially good at the 800 band and
another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.
I use a BNC T-connector to mount both antennas at the same time. I get
significant loss on the 800 MHz band when I do this. I might get loss
on the other bands from the other antenna also, but have not tested that
scenario yet.

My question is where does this loss come from? Is it the proximity of
the two antennas from one another (they are right next to each other
only a few inches apart). Or is it from the T connector itself? Asked
in a different way, if I used a jumper cable off the T so the two
antennas were separated by 6 feet of more, would I see a benefit or (if
the T connector is the problem) would there be no difference?




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S1mpleton
 

Watching


On Tue, Jan 12, 2021, 15:31 Mark Lewin <lewinm@...> wrote:
I have a question like Randy's but just the opposite situation.
I have one scanner but two antennas (both indoor).

I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high bands.  I have one antenna that is especially good at the 800 band and another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.  I use a BNC T-connector to mount both antennas at the same time. I get significant loss on the 800 MHz band when I do this.  I might get loss on the other bands from the other antenna also, but have not tested that scenario yet.

My question is where does this loss come from?  Is it the proximity of the two antennas from one another (they are right next to each other only a few inches apart). Or is it from the T connector itself?   Asked in a different way, if I used a jumper cable off the T so the two antennas were separated by 6 feet of more, would I see a benefit or (if the T connector is the problem) would there be no difference?




Scott, KB3JQQ
 

Most likely, it's leaking out the coax from the VHF antenna and the antenna.
Does the 800 come up if you disconnect the VHF antenna?

On 2021-01-12 15:19, Mark Lewin wrote:
I have a question like Randy's but just the opposite situation.
I have one scanner but two antennas (both indoor).

I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high bands.  I have one antenna that is especially good at the 800 band and another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.  I use a BNC T-connector to mount both antennas at the same time. I get significant loss on the 800 MHz band when I do this.  I might get loss on the other bands from the other antenna also, but have not tested that scenario yet.

My question is where does this loss come from?  Is it the proximity of the two antennas from one another (they are right next to each other only a few inches apart). Or is it from the T connector itself?   Asked in a different way, if I used a jumper cable off the T so the two antennas were separated by 6 feet of more, would I see a benefit or (if the T connector is the problem) would there be no difference?





S1mpleton
 

Thank you Joe. 
That kicked my brain and I now understand.
I am working on setting up a couple antennas and now know what to look for.

On Tue, Jan 12, 2021, 15:37 Joe M. <mch@...> wrote:
You want to use a device called a Diplexer to connect multiple antennas.
(that would be the 'best' equivalent of the previous case)

Your second antenna may be providing a 'short' of the 800 MHz signals.

I'm trying to think of a good analogy. Let's say you have a garden hose
with a splitter. Ideally, that would provide equal splitting to the two
hoses, but when one hose is larger it will such the water and leave the
smaller hose with little. Not the greatest example, but...

Google "RF shorting stub" and you will see. Your second antenna may
effectively be a shorted stub for 800 MHz signals and is nulling them.

Joe M.

On 1/12/2021 3:19 PM, Mark Lewin wrote:
> I have a question like Randy's but just the opposite situation.
> I have one scanner but two antennas (both indoor).
>
> I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high
> bands.  I have one antenna that is especially good at the 800 band and
> another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.
> I use a BNC T-connector to mount both antennas at the same time. I get
> significant loss on the 800 MHz band when I do this.  I might get loss
> on the other bands from the other antenna also, but have not tested that
> scenario yet.
>
> My question is where does this loss come from?  Is it the proximity of
> the two antennas from one another (they are right next to each other
> only a few inches apart). Or is it from the T connector itself?   Asked
> in a different way, if I used a jumper cable off the T so the two
> antennas were separated by 6 feet of more, would I see a benefit or (if
> the T connector is the problem) would there be no difference?
>
>
>
>
>
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>       Virus-free. www.avg.com
> <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient>
>
>
> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>






David Pilon
 

Mark,

If you have access to a low-pass filter tuned to around 500 MHz and a high-pass filter tuned to around 700 MHz, you might get this setup to work. Maybe take apart some UHF and 800 MHz flatpack duplexers?

You have constructive interference going on here due to the signals from each antenna arriving out-of-phase at the receiver.

Separating the antennas won’t help and will probably make the problem worse as the signals will be even farther out-of-phase.

Dave K8DTP 

Clear eyes, full hearts, can't lose.

On Jan 12, 2021, at 3:31 PM, Mark Lewin <lewinm@...> wrote:


I have a question like Randy's but just the opposite situation.
I have one scanner but two antennas (both indoor).

I have a Home Patrol 2 and I monitor VHF high, UHF low and UHF high bands.  I have one antenna that is especially good at the 800 band and another that is good in the 450MHz uhf low and 150-155 MHz VHF hi band.  I use a BNC T-connector to mount both antennas at the same time. I get significant loss on the 800 MHz band when I do this.  I might get loss on the other bands from the other antenna also, but have not tested that scenario yet.

My question is where does this loss come from?  Is it the proximity of the two antennas from one another (they are right next to each other only a few inches apart). Or is it from the T connector itself?   Asked in a different way, if I used a jumper cable off the T so the two antennas were separated by 6 feet of more, would I see a benefit or (if the T connector is the problem) would there be no difference?