I have 2 antennas for my repeater operation. 1 Tx and the other 1 Rx. Both frequencies are split 600KHz. My Question is if I have 1 cavity filter at the Rx section, will the performance of the Rx improve? I ask this Question because my repeater is getting some desense and got some problems on it.
My Tx antenna is 60 feet below my Rx antenna and the Tx performance is getting poor in some area. If there is 1 bandpass fillter at the Rx section, can I re-locate my Tx antenna 50 or 40 feet away from the Rx antenna and without any desense problem?
Thanks.
9W6AH
Repeater's Antennas with 1 cavity filter
Moderator: Queue Moderator
Repeater's Antennas with 1 cavity filter
I'm newbie and want to learn from the experties.
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raymond345
- Posts: 268
- Joined: Sat Sep 22, 2001 4:00 pm
60 feet Vertical/horizontal?
How much power on the tx unit?
What radios models?
What model of antenna/what gain?
What co-ax?
What radios models?
What model of antenna/what gain?
What co-ax?
If you are trying to do this as cheap as possible you need to put a
notch filter at the tx side set to the recieve freq. The reason for this
instead of a bandpass at the rx freq in the rx side is as follows.
The bandpass has to pass the rec freq to work at all. Therefore
ANY signal on the rec freq will get through. INCLUDING that part
of the broadband transmitter noise you dont want. If you put a
notch in the transmitter line at the freq of the receiver, then that
freq will be supressed or "sucked out" of the wideband noise
component of the transmitter and wont be present to get through
the front end of the rec including any pass filter cans you might
have there. So, for most "bang for buck" you need the notch.
If you go to a good book on antennas (ARRL has them) you can
find how to make trap or notch filters using stub pieces of old
hardline and a few connectors and capacitors.
Hope this may help. Phrawg
notch filter at the tx side set to the recieve freq. The reason for this
instead of a bandpass at the rx freq in the rx side is as follows.
The bandpass has to pass the rec freq to work at all. Therefore
ANY signal on the rec freq will get through. INCLUDING that part
of the broadband transmitter noise you dont want. If you put a
notch in the transmitter line at the freq of the receiver, then that
freq will be supressed or "sucked out" of the wideband noise
component of the transmitter and wont be present to get through
the front end of the rec including any pass filter cans you might
have there. So, for most "bang for buck" you need the notch.
If you go to a good book on antennas (ARRL has them) you can
find how to make trap or notch filters using stub pieces of old
hardline and a few connectors and capacitors.
Hope this may help. Phrawg
BBbzzzzz... ZAP.. GULP !!! ahhhh GOOD fly !
My two bits worth:
600Khz spacing requires about 100db isolation between the receiver and transmitter antenna ports.
This is accomplished with physical spacing of the antennas,
Duplexers, or a combination of the two.
In full duplex operation the quality of the antennas and cables become very important to the performance, and reliability of your system
I have used 50 foot co-linear vertical spacing on a tower.
The cables should be run on opposite tower legs.
Your cheap coax leaks, must be physically seperated.
Or 1/4 mile horizontal.
A cavity is always a good idea in both your transmitter and receiver.
Un fortunately at 600 kc spacing a pass cavity will have very little attenuation of the other frequency as you are within the band pass of the cavity.
That is why close spaced duplexers have some sort of reject design, with band pass filters. (Pass-Reject)
A 600 kc duplexer is rather large.
Notch filters can have very narrow reject band width.
Perhaps you could come up with some sort of reject filter to add to the physical isolation of the antennas.
The important measurement is receiver desense.
You will find that you have much desense.
Notice you can hear a radio in the field with out the transmitter on, gets noisy, or cuts out , or "water pumps" on weak signals.
(The receiver picks up a signal, keys the transmitter and defens its self., thus un keying, this repeats over and over.)
You should have NO degradiation when your transmitter is keyed.
I have a paper in word format on desense, yours for the asking
600Khz spacing requires about 100db isolation between the receiver and transmitter antenna ports.
This is accomplished with physical spacing of the antennas,
Duplexers, or a combination of the two.
In full duplex operation the quality of the antennas and cables become very important to the performance, and reliability of your system
I have used 50 foot co-linear vertical spacing on a tower.
The cables should be run on opposite tower legs.
Your cheap coax leaks, must be physically seperated.
Or 1/4 mile horizontal.
A cavity is always a good idea in both your transmitter and receiver.
Un fortunately at 600 kc spacing a pass cavity will have very little attenuation of the other frequency as you are within the band pass of the cavity.
That is why close spaced duplexers have some sort of reject design, with band pass filters. (Pass-Reject)
A 600 kc duplexer is rather large.
Notch filters can have very narrow reject band width.
Perhaps you could come up with some sort of reject filter to add to the physical isolation of the antennas.
The important measurement is receiver desense.
You will find that you have much desense.
Notice you can hear a radio in the field with out the transmitter on, gets noisy, or cuts out , or "water pumps" on weak signals.
(The receiver picks up a signal, keys the transmitter and defens its self., thus un keying, this repeats over and over.)
You should have NO degradiation when your transmitter is keyed.
I have a paper in word format on desense, yours for the asking
Aloha, Bernie
Add this to the other postings.
Here is a rule of thumb about repeater antenna spacing:
TABLE 1. MINIMUM ANTENNA SEPARATION.
Band 50MHz 144MHz 220MHz 440MHz
Vertical Separation 200' 50' 30' 20'
Horizontal Separation 2500' 800' 500' 250'
(sorry the chart didn't cut/n/paste very good)
Add the School of Hard Knox fudge factors, double the the values of the vertical separation. Most times it works. Like the others said, it depends on the antenna's, power, coax, how much out of band noise your xmtr makes, how good is the receiver, etc.
Unless you are on something like a TV station tower with lots of vertical to play with, a good duplexer can make it a lot easier.
..... the bat man
Here is a rule of thumb about repeater antenna spacing:
TABLE 1. MINIMUM ANTENNA SEPARATION.
Band 50MHz 144MHz 220MHz 440MHz
Vertical Separation 200' 50' 30' 20'
Horizontal Separation 2500' 800' 500' 250'
(sorry the chart didn't cut/n/paste very good)
Add the School of Hard Knox fudge factors, double the the values of the vertical separation. Most times it works. Like the others said, it depends on the antenna's, power, coax, how much out of band noise your xmtr makes, how good is the receiver, etc.
Unless you are on something like a TV station tower with lots of vertical to play with, a good duplexer can make it a lot easier.
..... the bat man
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psapengineer
- Posts: 175
- Joined: Thu Oct 07, 2004 10:00 am
Answer
The short answer is no. At 0.6 MHz you will need more than just a pass cavity in addition to the isolation you've gotten by vertical separation. You will likely need a pass/reject (pass/notch) on each leg. Good luck.
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raymond345
- Posts: 268
- Joined: Sat Sep 22, 2001 4:00 pm
Reject All the TIME
When we are not on RADIO HILL
we have used Reject only duplexers
on HAM 0.6mhz for 25 years.
They worked GREAT.
Remember it is not set-up on RF HILL.
we have used Reject only duplexers
on HAM 0.6mhz for 25 years.
They worked GREAT.
Remember it is not set-up on RF HILL.
My two bits worth:
In the early days, 30 years ago or so there were two duplexers with 600KC spacing that I was aware of:
The Sinclair F201G (I think) which was pass/reject, very expensive
with 4 large cavities.
DB had a notch duplexer with long skinny cans, 4,6,or more.
The ham repeater, a 50 Watt GE Prog line on the 8,000 ft level of Mauna Loa, on the big Island used 50' vertical spacing with no desense.
This was linked to Mt Halaakala, on Maui with a UHF Prog line.
Diamond Head on Oahu used 1/4 mile horizontal seperation.
We used a TV camera cable donated by a TV station.
A gun pill box on the crater rim to Hewling tunnel, a big gun placement in the side of the crater.
We use close spaced duplexers today.
In the early days, 30 years ago or so there were two duplexers with 600KC spacing that I was aware of:
The Sinclair F201G (I think) which was pass/reject, very expensive
with 4 large cavities.
DB had a notch duplexer with long skinny cans, 4,6,or more.
The ham repeater, a 50 Watt GE Prog line on the 8,000 ft level of Mauna Loa, on the big Island used 50' vertical spacing with no desense.
This was linked to Mt Halaakala, on Maui with a UHF Prog line.
Diamond Head on Oahu used 1/4 mile horizontal seperation.
We used a TV camera cable donated by a TV station.
A gun pill box on the crater rim to Hewling tunnel, a big gun placement in the side of the crater.
We use close spaced duplexers today.
Aloha, Bernie