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Is a Diplexer a Filter?

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richardc63

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Messages
222
Location
Sydney Australia
Hi all,

This is an ACMA type question...

I had an odd call from a radio inspector today arguing that the diplexer on our base did not constitute a filter, and therefore we were operating outside our licence conditions.

Has anyone received this sort of advice before?

I'm baffled as to how a diplexer works if it isn't a filter...

Cheers,


Richard
 
N

N_Jay

Guest
richardc63 said:
Hi all,

This is an ACMA type question...

I had an odd call from a radio inspector today arguing that the diplexer on our base did not constitute a filter, and therefore we were operating outside our licence conditions.

Has anyone received this sort of advice before?

I'm baffled as to how a diplexer works if it isn't a filter...

Cheers,


Richard
What type of filter are you supposed to have?

What type of "Diplexer"?

What type of station?
 

n8chb

Member
Joined
Nov 14, 2004
Messages
145
richardc63 said:
Hi all,

This is an ACMA type question...

I had an odd call from a radio inspector today arguing that the diplexer on our base did not constitute a filter, and therefore we were operating outside our licence conditions.

Has anyone received this sort of advice before?

I'm baffled as to how a diplexer works if it isn't a filter...

Cheers,


Richard

hi Richard,

I think you might have heard (the radio police) say duplexer and not diplexer because they are two differant things.

A duplexer is a cavity filter. It is tuned to isolate the transmitter from the reciever on a station using two differant frequencys on the same antenna. In your case the station would likely be a repeator recieving and transmitting simaltainusly on the same antenna and feed line.

A diplexer is often used to connect dual band mobile radios two antenna connections to a common feed line and antenna.

Anywho if you suspect your system is causing interferance or not working correctly it's important to have it checked as soon as possible by a qualifyed person.

A duplexer not tuned properly can cause damage to both a transmitter and reciever and also interference to other communication stations recievers. It's a commen complaint of a dirty signal getting into an other repeater systems input frequency.

You might want to have it checked before the fcc has to hire a field rep to come out and put you in radio jail.

73,

Roger - n8chb
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
Hi Roger,

I'm in Australia & we commonly call duplexers diplexers... I was referring to a repeater.

No, I don't think he is coming to lock me up... if he is the gaols will be full of radio techs.

My question was to fellow Aussies who have dealt with ACMA inspectors (I've been dealing with them for more than 20 years) and been told that a DUPLEXER is NOT a filter.

Thanks for the reply.

Regards,


Richard




n8chb said:
hi Richard,

I think you might have heard (the radio police) say duplexer and not diplexer because they are two differant things.

A duplexer is a cavity filter. It is tuned to isolate the transmitter from the reciever on a station using two differant frequencys on the same antenna. In your case the station would likely be a repeator recieving and transmitting simaltainusly on the same antenna and feed line.

A diplexer is often used to connect dual band mobile radios two antenna connections to a common feed line and antenna.

Anywho if you suspect your system is causing interferance or not working correctly it's important to have it checked as soon as possible by a qualifyed person.

A duplexer not tuned properly can cause damage to both a transmitter and reciever and also interference to other communication stations recievers. It's a commen complaint of a dirty signal getting into an other repeater systems input frequency.

You might want to have it checked before the fcc has to hire a field rep to come out and put you in radio jail.

73,

Roger - n8chb
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
Roger,

Just a little ps...

I am qualified.

The reason he rang me was to tell me that my repeater was interfering with a CDMA phone base (yes TELSTRA!) co-sited with my repeater and, wait for it, assigned the 2nd Harmonic of mine!

We've been there for 7 years, Telstra about 4... so I told him to get their frequency assignment changed.

Regards,


Richard
n8chb said:
hi Richard,

I think you might have heard (the radio police) say duplexer and not diplexer because they are two differant things.

A duplexer is a cavity filter. It is tuned to isolate the transmitter from the reciever on a station using two differant frequencys on the same antenna. In your case the station would likely be a repeator recieving and transmitting simaltainusly on the same antenna and feed line.

A diplexer is often used to connect dual band mobile radios two antenna connections to a common feed line and antenna.

Anywho if you suspect your system is causing interferance or not working correctly it's important to have it checked as soon as possible by a qualifyed person.

A duplexer not tuned properly can cause damage to both a transmitter and reciever and also interference to other communication stations recievers. It's a commen complaint of a dirty signal getting into an other repeater systems input frequency.

You might want to have it checked before the fcc has to hire a field rep to come out and put you in radio jail.

73,

Roger - n8chb
 

Al42

Member
Joined
Apr 29, 2005
Messages
3,485
Location
Long Island, NY, USA
I'd look for something non-linear that recently developed, if the problem is recent. Like a poor connection between two pieces of metal or some rust on a joint. Anything that can rectify that's near the transmitting antenna (or even near the transmitter itself) could shoot a little second harmonic into the ether (or is that aether down there?)

But two systems colocated and harmonically related? Sounds like good planning to me - for a government.
 
N

N_Jay

Guest
Duplexers may or maynot provide the neccessary filtering.

Have them tell you what specs you must meet. then look at the duplexer specs and see what you ahve to add.
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
Hi N Jay,

His opening comment was "Your equipment has gone spurious".

My next question was "Is my equipment operating outside of Specification?"

After an embarassed silence... "Probably not."

I say "Then it isn't spurious."

He says "It is spurious- they can hear your 2nd Harmonic!"

My response was "Do you know an FM transmitter that doesn't have one!"

Loud grumbling from down the line...

"So you aren't going to do anything about it?"

"I will if it isn't in Spec."

That is when he spang back "But you are in breach of your licence conditions because you don't have a filter...."

Unfortunately I pointed out to him that at most of our 140 base sites we have a duplexer (Tx-Rx or similiar and of various types, usually Pseudo Bandpass) ... with no additional cavity unless a problem justifies one... I told him he is going to get writers cramp from writing out the Infringement Notices!

He isn't the brightest light bulb in the universe...

Now on the filter specs... at the 2nd harmonic a 1/4 wave would be a 1/2 wave... so wouldn't the filter have little impact if placed on our transmitter? Isn't it really a simple frequency assignment stuff up? They shouldn't be co-sited.

Regards,


Richard

N_Jay said:
Duplexers may or maynot provide the neccessary filtering.

Have them tell you what specs you must meet. then look at the duplexer specs and see what you ahve to add.
 
N

N_Jay

Guest
I would ask EXACTLY how many db you need to surpress by.

Make it sound like you are trying to be helpfull.
"I would hate to keep having this problem, so I need to know what the specs need to be"
Then ask the cellular company to pay! ;)
 

n8chb

Member
Joined
Nov 14, 2004
Messages
145
richardc63 said:
Hi Roger,

I'm in Australia & we commonly call duplexers diplexers... I was referring to a repeater.

No, I don't think he is coming to lock me up... if he is the gaols will be full of radio techs.

My question was to fellow Aussies who have dealt with ACMA inspectors (I've been dealing with them for more than 20 years) and been told that a DUPLEXER is NOT a filter.

Thanks for the reply.

Regards,


Richard
Hello agn,

Didn't realize U were in ZL/VK land

Thanks fer the correction and now I know that a duplexer is not allways a duplexer
it could be a diplexer depending on what part of the globe one is standing. hi

Nice to meet you Richard,

Roger the dodger
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
Hi N Jay,

I told him that if we were in Spec they could provide the filtering to be fitted to our equipment... we would never refuse to co-operate. However there is an important principle to defend that just because the complainant happens to be the largest carrier in the country, they shouldn't expect others to fix up THEIR mistake.

But you have to wonder about the competence of the radio inspector!

Cheers,


Richard
N_Jay said:
I would ask EXACTLY how many db you need to surpress by.

Make it sound like you are trying to be helpfull.
"I would hate to keep having this problem, so I need to know what the specs need to be"
Then ask the cellular company to pay! ;)
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
Thanks for your advice anyway Roger- and I'll remember to call them duplexers on US lists!

Cheers,


Richard
n8chb said:
Hello agn,

Didn't realize U were in ZL/VK land

Thanks fer the correction and now I know that a duplexer is not allways a duplexer
it could be a diplexer depending on what part of the globe one is standing. hi

Nice to meet you Richard,

Roger the dodger
 

richardc63

Member
Joined
Aug 1, 2005
Messages
222
Location
Sydney Australia
richardc63 said:
Hi N Jay,

I told him that if we were in Spec they could provide the filtering to be fitted to our equipment... we would never refuse to co-operate. However there is an important principle to defend that just because the complainant happens to be the largest carrier in the country, they shouldn't expect others to fix up THEIR mistake.

But you have to wonder about the competence of the radio inspector!

Cheers,


Richard
Hi all,

Just a little follow up to let people know how this matter is being pursued...

It turns out the the specified performance of transmitters in Australia are defined in Australian Standard AS4295.

For a base station transmitter AS4295 specifies the maximum total harmonic radiation as -30dBm measured at the transmitter output.

The equipment manufacturer assures me that the equipment spec is -33dBm.

We did some quick calculations and, allowing for the existing duplexer and free space loss (about 30ft horizontal) at the receiver the second harmonic should be about -100dBm.

So the problem is one of a very poor frequency assignment of the CDMA base.

Still, we are making the fix by installing a single 4 inch cavity on our transmitter that should give us 50dB attenuation at the 2nd harmonic. This should fix it. At the end of the day it is cheaper to spend abou $300 on the cavity (plus 1000km of travel) than to argue about who should pay for the fix...

Thought some of you might be interested...

Cheers,


Richard
 
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