Question for the moto gurus or anyone else. Have an application with a UHF 460mhz repeater getting hammered / desensed by 700-750mhz cell tower that is 50'-75' ft away at the same elevation. Current duplexer isn't cutting the mustard apparently and I'm curious if a moto or similar UHF preselector would help or need look into a 700-750 band reject filter on the rx side? Have not looked at the extended band reject portion of the curve on a preselector for some time and what its like up that far. Thanks in advance!
-
To anyone looking to acquire commercial radio programming software:
Please do not make requests for copies of radio programming software which is sold (or was sold) by the manufacturer for any monetary value. All requests will be deleted and a forum infraction issued. Making a request such as this is attempting to engage in software piracy and this forum cannot be involved or associated with this activity. The same goes for any private transaction via Private Message. Even if you attempt to engage in this activity in PM's we will still enforce the forum rules. Your PM's are not private and the administration has the right to read them if there's a hint to criminal activity.
If you are having trouble legally obtaining software please state so. We do not want any hurt feelings when your vague post is mistaken for a free request. It is YOUR responsibility to properly word your request.
To obtain Motorola software see the Sticky in the Motorola forum.
The various other vendors often permit their dealers to sell the software online (i.e., Kenwood). Please use Google or some other search engine to find a dealer that sells the software. Typically each series or individual radio requires its own software package. Often the Kenwood software is less than $100 so don't be a cheapskate; just purchase it.
For M/A Com/Harris/GE, etc: there are two software packages that program all current and past radios. One package is for conventional programming and the other for trunked programming. The trunked package is in upwards of $2,500. The conventional package is more reasonable though is still several hundred dollars. The benefit is you do not need multiple versions for each radio (unlike Motorola).
This is a large and very visible forum. We cannot jeopardize the ability to provide the RadioReference services by allowing this activity to occur. Please respect this.
Motorola UHF Preselector out of band rejection question
- Thread starter brushfire21
- Start date
What model repeater? What make/model duplexer?
rescuecomm
Member
The old Micor front ends were pretty tight, but it sounds like you need a large pass-band cavity tuned for your receive frequency. A reject cavity would help if you can identify a spur.
RFI-EMI-GUY
Member
- Joined
- Dec 22, 2013
- Messages
- 7,264
To answer your question it would really help to know what kind of repeater this is, details about the receiver and existing filters.
freddaniel
Member
You are correct, a three to six series resonator pre-selector would resolve your problem, between the duplexer and the receiver. Something like a transmitter or receiver filter from an old Motorola radio. Even an old GE Mastr II front end would likely work. Far cheaper than a new Sinclair.
Fred
Fred
In my experience these window filter resonators have high insertion loss on the order of 1.5 to 4dB. I think a better approach is a full size 1/4 wave cavity which has more like .5dB insertion loss and very narrow band width. These show up used in the $75 range all the time.
RFI-EMI-GUY
Member
- Joined
- Dec 22, 2013
- Messages
- 7,264
Filters and cavities can have spurious responses where higher frequencies can leak through, albeit with high insertion loss. The OP has not given enough specifics. Also OP has apparently left the building.
My apologies, for some reason I wasn't getting updates via email to know I got responses. I just snagged off fleabay a quantar UHF preselector that has 1.55db insertion loss and about 90db of rejection between 469 MHz and 750mhz from the ATT tower next door.
Not enthused with the 1.55 loss but in the big picture it's better then a deaf/over loaded front end and takes care of anything in the nearby vicinity.
This is an Icom FR4000 repeater and sadly only has a simple band reject flat pack and the owner/friend is lacking funds. Though I'm not sure how much a BpBr would help but it would be better then what's there.
As there was no other UHF equipment at this site until a few years ago, the flat pak was fine. Verizon and ATT both upgraded and added additional bands to the towers in the 700-850mhz and appears that's causing issues.
the freq pass is about 1-1.5mhz at 469 MHz and then from 30mhz to 2.1ghz is 80-90db rejection and fairly flat. Will know next week how well it does but suspect it will go along way in restoring some recieve sensitivity.
Not enthused with the 1.55 loss but in the big picture it's better then a deaf/over loaded front end and takes care of anything in the nearby vicinity.
This is an Icom FR4000 repeater and sadly only has a simple band reject flat pack and the owner/friend is lacking funds. Though I'm not sure how much a BpBr would help but it would be better then what's there.
As there was no other UHF equipment at this site until a few years ago, the flat pak was fine. Verizon and ATT both upgraded and added additional bands to the towers in the 700-850mhz and appears that's causing issues.
the freq pass is about 1-1.5mhz at 469 MHz and then from 30mhz to 2.1ghz is 80-90db rejection and fairly flat. Will know next week how well it does but suspect it will go along way in restoring some recieve sensitivity.
lenk911
Member
Let me share with you the old radio engineer's rule of thumb: Generally 2/3 rds (of the db's) of the filtering to solve interference issues usually will reside in the offending transmitter, 1/3 in the offended receiver.
You need to FIRST determine whether your interference is transmitter sideband noise, receiver desense, a spur, intermodulation or an image. Just stacking filtering in your receiver circuit is not a solution. All it does it make you feel like you have accomplished something but you may have just further numbed your receiver.
Because of the frequency separation (460 verses 750 MHZ) I would first look to another transmitter 50% between the two frequencies (~605 MHZ) for potential intermod. Then look to the 25 and 75% points (i.e. 532.5 677.5) for a transmitter.
The intermod may be mixing in your radio system. Check for non-linear connections, oxidation, bi-metallic connectors, poor installation practices etc. Is your transmitter a player in the problem?
An old engineer once taught me that 80% of a radio system problem solving is done with your mind, 20% with your hands. Good luck!
You need to FIRST determine whether your interference is transmitter sideband noise, receiver desense, a spur, intermodulation or an image. Just stacking filtering in your receiver circuit is not a solution. All it does it make you feel like you have accomplished something but you may have just further numbed your receiver.
Because of the frequency separation (460 verses 750 MHZ) I would first look to another transmitter 50% between the two frequencies (~605 MHZ) for potential intermod. Then look to the 25 and 75% points (i.e. 532.5 677.5) for a transmitter.
The intermod may be mixing in your radio system. Check for non-linear connections, oxidation, bi-metallic connectors, poor installation practices etc. Is your transmitter a player in the problem?
An old engineer once taught me that 80% of a radio system problem solving is done with your mind, 20% with your hands. Good luck!
freddaniel
Member
Well, did your Quantar pre-selector fix your problem, or is the interference broadband noise [on channel] or intermod?