[Repeater-Builder] Re: Receiver overload
David, I had a similar problem with a 2 meter repeater at a high power FM site. When the FM broadcast transmitter was down the front end overload of my receiver (GE mastrII) went away. In my case it turned out to be RF from the FM transmitter floating on the AC power lines and making its way into my repeaters receiver. I added an AC line filter and a LC filter to the 12VDC line and my problem was cured. Perhaps you could try running your receiver on a battery to isolate it from the AC line. Jim KC3LW --- In Repeater-Builder@yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
RE: [Repeater-Builder] Re: Receiver overload
The instructions for constructing a simple, but very effective, stub filter are found in General Electric Datafile Bulletin 10002-1, available for download here: www.repeater-builder.com/ge/datafile-bulletin/df-10002-01.pdf I used the piston variable capacitor out of a bad channel element for tuning. Worked like a champ! 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike Morris WA6ILQ Sent: Thursday, November 22, 2007 11:58 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Receiver overload At 09:46 PM 11/22/07, you wrote: --- In Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com , David Epley [EMAIL PROTECTED] wrote: What is your opinion on a ¼ wave open stub installed in the receiver side cut for 104.9?
[Repeater-Builder] Re: Receiver overload
What about one of those shorted stub type lightning arresters for 900 mhz on the antenna side, and the stub to notch out the 104 mhz on the receiver side of the duplexer. For the 104 mhz comming in on the outside of the sheild/cable, some good ferrite chokes over the receiver cable.
[Repeater-Builder] Re: Receiver overload
The 900 MHz Maxtrac receiver's IF is 45.1 MHz I believe. Have you looked around there for any possible signals? And are there any studio transmitter links around 947-950 MHz? --- In Repeater-Builder@yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
RE: [Repeater-Builder] Re: Receiver overload
Yes I have looked + and - the IF for a signal _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Steve Sent: Thursday, November 22, 2007 11:10 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload The 900 MHz Maxtrac receiver's IF is 45.1 MHz I believe. Have you looked around there for any possible signals? And are there any studio transmitter links around 947-950 MHz? --- In Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
[Repeater-Builder] Re: Receiver overload
If you're sure the just rf at the front end of receiver is the entire problem..? Install a High-Q Notch cavity (with a probe dc ground return) on the receiver and try a 3dB pad (on the receiver) to start things out. I sourced a similar problem with a Yaesu/Vertex repeater... their receivers like many other brands always seem to be red-hot with front end gain. The problem required a combination of the cavity and the eventual 1dB value attenuator pad remaining in place. cheers, s. David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
[Repeater-Builder] Re: Receiver overload
In this case... I would expect the band-pass cavity option to be a popcorn fart. See my post about the High-Q notch cavity (with the dc return probe) and the attenuator, which should help if the problem is source to the RF coming in the coax port is the sole source. s. David Epley [EMAIL PROTECTED] wrote: I just tried a pair of Celwave 8 inch band pass cavities with no noticeable improvement. David N9CZV _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jim Brown Sent: Thursday, November 22, 2007 6:13 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Receiver overload David, try using one or two band pass only cavaties in the receive side instead of the BpBr type. The BpBr filters often do not discriminate against signals far off the pass frequency, and you may not be getting enough rejection out of your input cavities. 73 - Jim W5ZIT --- David Epley [EMAIL PROTECTED] mailto:depley%40starband.net net wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana __ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview. http://overview.mail.yahoo.com/ mail.yahoo.com/
[Repeater-Builder] Re: Receiver overload
I think your title says it, overload. Parelectronics makes a little 3 pole filter, is that the one you tried? You can tweak all 3 poles to 104.9 for about 50 db attnuation. http://www.parelectronics.com/vhf-fm.htm A shorted stub would be easy to try too, there are several designs. Since the FM freq is so far away, try putting a T in line and a half wave (at 104.9) length of coax (times the velocity factor) on the T. Start long and work your way along the coax from the end with a pin and stick it in and short the coax while watching the FM signal on the spec anyl. Find the best null, then cut and solder and check the insertion loss at your 900 freq. ... Keith WE6R --- In Repeater-Builder@yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
[Repeater-Builder] Re: Receiver overload
The Devil is in the details... I glazed over the original post and just noticed. David Epley [EMAIL PROTECTED] wrote: My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Using the converted Maxtrac Mobile might just be the fly in your soup. It's ability to deal with these type of receiver gremlins in less than ideal RF Locations is not so great. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. The question is... do you know exactly what that degradation is? As an example... is your receiver being blocked? is the problem based directly from the broadcast frequency? Sections of the receiver being overwhelmed by shear RF Levels and/or some specific section/stage within the receiver suffering from another issue? When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers Place a band-pass cavity on the FM-Broadcast frequency (if you have one) or a 10 dB pad if you don't and park your service monitor (or similar animal) on the 900 MHz antenna(s) to measure how much on the broadcast channel RF (only) you have at the front end of your 900 MHz receiver. Since you can see differences in the problem by using different antennas (which have different isolation values from the problem signal), I would probably say there is possible hope you can resolve this problem. added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. I would expect the Bp BpBr cavity options to not bear the desired results... Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. Bingo... well a partial bingo. Terms like receiver overloading and blocking can be throw out/around with really knowing the exact cause/source/problem. So be careful and don't go down a single path, which might be the wrong one. Per my above comment... what would be handy to know is the BC Station level at on all the 900 antennas and correspond those relative values to the degradation you measure from the receiver effective sensitivity (in operation on those antennas). I was wondering if a stub cut for the broadcast frequency would work. Probably not enough... you would normally need at least one (or more) very, very High-Q notch cavity (tuned to the BC channel) in place (on the 900 antenna system). Any thoughts would be greatly appreciated. White wine is overrated... cheers, s.
RE: [Repeater-Builder] Re: Receiver overload
I have a handful of different size attenuators and will try in the morning. _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 2:03 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload If you're sure the just rf at the front end of receiver is the entire problem..? Install a High-Q Notch cavity (with a probe dc ground return) on the receiver and try a 3dB pad (on the receiver) to start things out. I sourced a similar problem with a Yaesu/Vertex repeater... their receivers like many other brands always seem to be red-hot with front end gain. The problem required a combination of the cavity and the eventual 1dB value attenuator pad remaining in place. cheers, s. David Epley [EMAIL PROTECTED] wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
RE: [Repeater-Builder] Re: Receiver overload
I am looking for a cavity now _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 2:07 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload In this case... I would expect the band-pass cavity option to be a popcorn fart. See my post about the High-Q notch cavity (with the dc return probe) and the attenuator, which should help if the problem is source to the RF coming in the coax port is the sole source. s. David Epley [EMAIL PROTECTED] wrote: I just tried a pair of Celwave 8 inch band pass cavities with no noticeable improvement. David N9CZV _ From: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com [mailto:Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com] On Behalf Of Jim Brown Sent: Thursday, November 22, 2007 6:13 AM To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: Re: [Repeater-Builder] Receiver overload David, try using one or two band pass only cavaties in the receive side instead of the BpBr type. The BpBr filters often do not discriminate against signals far off the pass frequency, and you may not be getting enough rejection out of your input cavities. 73 - Jim W5ZIT --- David Epley [EMAIL PROTECTED] mailto:depley%40starband.net net wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana __ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview. http://overview. http://overview.mail.yahoo.com/ mail.yahoo.com/ mail.yahoo.com/
[Repeater-Builder] Re: Receiver overload
As a generic rule of thumb... the larger the cavity diameter the higher the internal Q. If nothing else don't forget you can use low band cavities in the 3/4 wave mode. Trying to find an min 8 to 15 inch diameter notch cavity on 104 MHz might be a bit of fun for the average Joe. As an example... cavities for broadcast work are often the size of the average home shower stall. And they get real warm in operation. Since you're not using it in the BC transmitter pipe (hard-line), you don't need to worry about the unwieldy physical size bottles. But you do need as High-Q cavity as you can find. One other last though... you might be able to make enough of a notch function using sections of 1-5/8 inch hard line as in the same example we see with folks making low-band duplexers. cheers, skipp David Epley [EMAIL PROTECTED] wrote: I am looking for a cavity now _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 2:07 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload In this case... I would expect the band-pass cavity option to be a popcorn fart. See my post about the High-Q notch cavity (with the dc return probe) and the attenuator, which should help if the problem is source to the RF coming in the coax port is the sole source. s. David Epley depley@ wrote: I just tried a pair of Celwave 8 inch band pass cavities with no noticeable improvement. David N9CZV _ From: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com [mailto:Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com] On Behalf Of Jim Brown Sent: Thursday, November 22, 2007 6:13 AM To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: Re: [Repeater-Builder] Receiver overload David, try using one or two band pass only cavaties in the receive side instead of the BpBr type. The BpBr filters often do not discriminate against signals far off the pass frequency, and you may not be getting enough rejection out of your input cavities. 73 - Jim W5ZIT --- David Epley [EMAIL PROTECTED] mailto:depley%40starband.net net wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana __ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview. http://overview. http://overview.mail.yahoo.com/ mail.yahoo.com/ mail.yahoo.com/
Re: [Repeater-Builder] Re: Receiver overload
Trying to get a notch cavity for 104 MHz that will pass 900 MHz might be a problem. Also using coax as a notch one has to make sure it does not do same at 900 MHz. A 1/4 wave at 104 MHz has lots of notches at the high frequencies, but I would give it a try. A bandpass at 900 would probably be an easier choice, but think this has been tried. 73, ron, n9ee/r From: skipp025 [EMAIL PROTECTED] Date: 2007/11/22 Thu PM 01:47:43 CST To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload As a generic rule of thumb... the larger the cavity diameter the higher the internal Q. If nothing else don't forget you can use low band cavities in the 3/4 wave mode. Trying to find an min 8 to 15 inch diameter notch cavity on 104 MHz might be a bit of fun for the average Joe. As an example... cavities for broadcast work are often the size of the average home shower stall. And they get real warm in operation. Since you're not using it in the BC transmitter pipe (hard-line), you don't need to worry about the unwieldy physical size bottles. But you do need as High-Q cavity as you can find. One other last though... you might be able to make enough of a notch function using sections of 1-5/8 inch hard line as in the same example we see with folks making low-band duplexers. cheers, skipp David Epley [EMAIL PROTECTED] wrote: I am looking for a cavity now _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 2:07 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload In this case... I would expect the band-pass cavity option to be a popcorn fart. See my post about the High-Q notch cavity (with the dc return probe) and the attenuator, which should help if the problem is source to the RF coming in the coax port is the sole source. s. David Epley depley@ wrote: I just tried a pair of Celwave 8 inch band pass cavities with no noticeable improvement. David N9CZV _ From: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com [mailto:Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com] On Behalf Of Jim Brown Sent: Thursday, November 22, 2007 6:13 AM To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: Re: [Repeater-Builder] Receiver overload David, try using one or two band pass only cavaties in the receive side instead of the BpBr type. The BpBr filters often do not discriminate against signals far off the pass frequency, and you may not be getting enough rejection out of your input cavities. 73 - Jim W5ZIT --- David Epley [EMAIL PROTECTED] mailto:depley%40starband.net net wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana __ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview. http://overview. http://overview.mail.yahoo.com/ mail.yahoo.com/ mail.yahoo.com/ Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
[Repeater-Builder] Re: Receiver overload
David, I suspect that the issue is 104.9 mhz energy coming down the outside of the feedline and into your receiver. As others have mentioned the maxtrac has a lot of plastic. A shielded box with no unbypassed wires going in and out may help. Ferrites on the feedline or a coil in the feedline may help as well as some more grounds on the feedline. There are also isolation transformers that could be used at 900 mhz. but they are rare. Mini Circuits may have them. I once had to mount a UHF Micor receiver in a shielded box as it picked up cell phones otherwise. I have operated amateur repeaters in broadcast facilities since the 1970's. It's not unusual to measure +30 or even +40 dbm coming down a feedline from an antenna mounted not far from an FM broadcasting antenna. I have been bitten with RF burns from such feedlines more than one. I have enjoyed much success getting rid of these problems with just a 1/4 wave shorted stub at the repeater frequencies. However, this apparently is not your situation. With all the things you've tried to no avail, any 104.9 mhz. energy on the inside of the feedline doesn't sound like the culprit. That's why I think it is RF on the shield. I have been in a great many broadcasting facilities. Many are very well done with much attention to details. You could eat off the floor and feel good about it. But many are a real pit with little attention to detail - just get it on the air. The grounding in these installations is next to non-existant. Having not seen your neigbor's setup on 104.9, I can't evaluate it. I also don't know the amount of grounding and bypassing on your 900 mhz. setup. But, based on my experience, I would suspect a feedline hot with RFon its outside. It might be interesting to visit your neighbor and see how he is receiving his 940 mhz. studio-transmitter link, which is apparently unaffected by his 104.9 mhz. transmitter. Al, K9SI, BC Engineer/consultant, RETIRED! David Epley wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
RE: [Repeater-Builder] Re: Receiver overload
What is your opinion on a ¼ wave open stub installed in the receiver side cut for 104.9? _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Al Wolfe Sent: Thursday, November 22, 2007 5:50 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload David, I suspect that the issue is 104.9 mhz energy coming down the outside of the feedline and into your receiver. As others have mentioned the maxtrac has a lot of plastic. A shielded box with no unbypassed wires going in and out may help. Ferrites on the feedline or a coil in the feedline may help as well as some more grounds on the feedline. There are also isolation transformers that could be used at 900 mhz. but they are rare. Mini Circuits may have them. I once had to mount a UHF Micor receiver in a shielded box as it picked up cell phones otherwise. I have operated amateur repeaters in broadcast facilities since the 1970's. It's not unusual to measure +30 or even +40 dbm coming down a feedline from an antenna mounted not far from an FM broadcasting antenna. I have been bitten with RF burns from such feedlines more than one. I have enjoyed much success getting rid of these problems with just a 1/4 wave shorted stub at the repeater frequencies. However, this apparently is not your situation. With all the things you've tried to no avail, any 104.9 mhz. energy on the inside of the feedline doesn't sound like the culprit. That's why I think it is RF on the shield. I have been in a great many broadcasting facilities. Many are very well done with much attention to details. You could eat off the floor and feel good about it. But many are a real pit with little attention to detail - just get it on the air. The grounding in these installations is next to non-existant. Having not seen your neigbor's setup on 104.9, I can't evaluate it. I also don't know the amount of grounding and bypassing on your 900 mhz. setup. But, based on my experience, I would suspect a feedline hot with RFon its outside. It might be interesting to visit your neighbor and see how he is receiving his 940 mhz. studio-transmitter link, which is apparently unaffected by his 104.9 mhz. transmitter. Al, K9SI, BC Engineer/consultant, RETIRED! David Epley wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
Re: RE: [Repeater-Builder] Re: Receiver overload
An open qtr wave at 104.5 will notch out 104.5, but make sure it is not off muliple qtr wave at your 925/905 freq or it could notch it out also. Just have to do the calculation. Qtr wave with .66 velocity factor cable at 104.5 MHz is about 1.55 ft. I believe this is 9 qtr wavelengths at 940.5 MHz notching it out also. The skirts on this low Q filter might be a factor. 73, ron, n9ee/r From: David Epley [EMAIL PROTECTED] Date: 2007/11/22 Thu PM 05:18:42 CST To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Receiver overload What is your opinion on a ¼ wave open stubinstalled in the receiver side cut for 104.9? From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Al Wolfe Sent: Thursday, November 22, 20075:50 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re:Receiver overload David, I suspect that the issue is 104.9 mhz energy coming down the outside of the feedline and into your receiver. As others have mentioned the maxtrac has a lot of plastic. A shielded box with no unbypassed wires going in and out may help. Ferrites on the feedline or a coil in the feedline may help as well as some more grounds on the feedline. There are also isolation transformers that could be used at 900 mhz. but they are rare. Mini Circuits may have them. I once had to mount a UHF Micor receiver in a shielded box as it picked up cell phones otherwise. I have operated amateur repeaters in broadcast facilities since the 1970's. It's not unusual to measure +30 or even +40 dbm coming down a feedline from an antenna mounted not far from an FM broadcasting antenna. I have been bitten with RF burns from such feedlines more than one. I have enjoyed much success getting rid of these problems with just a 1/4 wave shorted stub at the repeater frequencies. However, this apparently is not your situation. With all the things you've tried to no avail, any 104.9 mhz. energy on the inside of the feedline doesn't sound like the culprit. That's why I think it is RF on the shield. I have been in a great many broadcasting facilities. Many are very well done with much attention to details. You could eat off the floor and feel good about it. But many are a real pit with little attention to detail - just get it on the air. The grounding in these installations is next to non-existant. Having not seen your neigbor's setup on 104.9, I can't evaluate it. I also don't know the amount of grounding and bypassing on your 900 mhz. setup. But, based on my experience, I would suspect a feedline hot with RFon its outside. It might be interesting to visit your neighbor and see how he is receiving his 940 mhz. studio-transmitter link, which is apparently unaffected by his 104.9 mhz. transmitter. Al, K9SI, BC Engineer/consultant, RETIRED! David Epley wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
[Repeater-Builder] Re: Receiver overload
I think you may be on the right track with a ¼ wave open stub between the duplexer and the receiver. try and use a good low loss piece of coax for the stub...like ¼ or half inch superflex the lower loss the higher Q the notch will be. start a bit long and shorten it a bit at a time to tune. The reason that I Know this kind of thing will work for some types of problems is that I had the exact reverse happen to me. I had a 900 Mhz Paging transmitter getting into my 2 meter repeater a few years ago. I cured it with a BNC TEE and a very short piece of RG58 I got close to 27 or so db of notch at the Paging transmitter frequency and it cured the problem...This thing was getting into the front end of a GE MASTRII Receiver...It was one of thoes crappy third party 900 transmitters built FOR MOTOROLA by someone else. This fix is real cheap can't hurt to try. AC0Y --- In Repeater-Builder@yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: What is your opinion on a ¼ wave open stub installed in the receiver side cut for 104.9? _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Al Wolfe Sent: Thursday, November 22, 2007 5:50 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload David, I suspect that the issue is 104.9 mhz energy coming down the outside of the feedline and into your receiver. As others have mentioned the maxtrac has a lot of plastic. A shielded box with no unbypassed wires going in and out may help. Ferrites on the feedline or a coil in the feedline may help as well as some more grounds on the feedline. There are also isolation transformers that could be used at 900 mhz. but they are rare. Mini Circuits may have them. I once had to mount a UHF Micor receiver in a shielded box as it picked up cell phones otherwise. I have operated amateur repeaters in broadcast facilities since the 1970's. It's not unusual to measure +30 or even +40 dbm coming down a feedline from an antenna mounted not far from an FM broadcasting antenna. I have been bitten with RF burns from such feedlines more than one. I have enjoyed much success getting rid of these problems with just a 1/4 wave shorted stub at the repeater frequencies. However, this apparently is not your situation. With all the things you've tried to no avail, any 104.9 mhz. energy on the inside of the feedline doesn't sound like the culprit. That's why I think it is RF on the shield. I have been in a great many broadcasting facilities. Many are very well done with much attention to details. You could eat off the floor and feel good about it. But many are a real pit with little attention to detail - just get it on the air. The grounding in these installations is next to non-existant. Having not seen your neigbor's setup on 104.9, I can't evaluate it. I also don't know the amount of grounding and bypassing on your 900 mhz. setup. But, based on my experience, I would suspect a feedline hot with RFon its outside. It might be interesting to visit your neighbor and see how he is receiving his 940 mhz. studio-transmitter link, which is apparently unaffected by his 104.9 mhz. transmitter. Al, K9SI, BC Engineer/consultant, RETIRED! David Epley wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana
[Repeater-Builder] Re: Receiver overload
--- In Repeater-Builder@yahoogroups.com, David Epley [EMAIL PROTECTED] wrote: What is your opinion on a ¼ wave open stub installed in the receiver side cut for 104.9? David, This is the first thing I'd try. I have much success using stubs to eliminate problems such as yours. However, it won't help much in the case of common mode problems which yours may very well be. Shielding and grounding may be your best solution in that case. I once had a Heathkit freq counter that picked up our FM transmitter when connected to anything. A 1/4 wave open stub and tee at the input cured the problem. I've also used them on FM receivers at the station to knock down our signal enough to listen to other stations. An open stub at the FM station's frequency hooked to your 900 receiver will add some reactance to the line but that should not be too much of a problem unless it comes out as an even multiple of a half wavelength at your 900 freq. Al, K9SI
RE: [Repeater-Builder] Re: Receiver overload
70s Rock _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 10:11 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload Anyone bother to ask what format is playing on the broadcast station? You could have some hip-hop or thug music playing and that could be a potential problem? :-) s. Are you sure that 104.9 (WINN?) is the only FM station near your repeater? Looking at the data, it looks like 100.3 WYGB is possibly on the same tower. This is assuming that your repeater is in Columbus, IN.
[Repeater-Builder] Re: Receiver overload
Anyone bother to ask what format is playing on the broadcast station? You could have some hip-hop or thug music playing and that could be a potential problem? :-) s. Are you sure that 104.9 (WINN?) is the only FM station near your repeater? Looking at the data, it looks like 100.3 WYGB is possibly on the same tower. This is assuming that your repeater is in Columbus, IN.
Re: [Repeater-Builder] Re: Receiver overload
In NZ we used to have VHF repeater services on 101-108 MHz (AM) and there were quite a number of surplus cavity filters floating around from the old TX combiners and RX multicouplers. If you are in need of something email me off list. Cheers _ Gareth Bennett This e-mail is confidential, if you received this message in error, or you are not the intended recipient, please return it to the sender and destroy any copies. Thank you. - Original Message - From: skipp025 To: Repeater-Builder@yahoogroups.com Sent: Friday, November 23, 2007 8:47 AM Subject: [Repeater-Builder] Re: Receiver overload As a generic rule of thumb... the larger the cavity diameter the higher the internal Q. If nothing else don't forget you can use low band cavities in the 3/4 wave mode. Trying to find an min 8 to 15 inch diameter notch cavity on 104 MHz might be a bit of fun for the average Joe. As an example... cavities for broadcast work are often the size of the average home shower stall. And they get real warm in operation. Since you're not using it in the BC transmitter pipe (hard-line), you don't need to worry about the unwieldy physical size bottles. But you do need as High-Q cavity as you can find. One other last though... you might be able to make enough of a notch function using sections of 1-5/8 inch hard line as in the same example we see with folks making low-band duplexers. cheers, skipp David Epley [EMAIL PROTECTED] wrote: I am looking for a cavity now _ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of skipp025 Sent: Thursday, November 22, 2007 2:07 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Receiver overload In this case... I would expect the band-pass cavity option to be a popcorn fart. See my post about the High-Q notch cavity (with the dc return probe) and the attenuator, which should help if the problem is source to the RF coming in the coax port is the sole source. s. David Epley depley@ wrote: I just tried a pair of Celwave 8 inch band pass cavities with no noticeable improvement. David N9CZV _ From: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com [mailto:Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com] On Behalf Of Jim Brown Sent: Thursday, November 22, 2007 6:13 AM To: Repeater-Builder@ mailto:Repeater-Builder%40yahoogroups.com yahoogroups.com Subject: Re: [Repeater-Builder] Receiver overload David, try using one or two band pass only cavaties in the receive side instead of the BpBr type. The BpBr filters often do not discriminate against signals far off the pass frequency, and you may not be getting enough rejection out of your input cavities. 73 - Jim W5ZIT --- David Epley [EMAIL PROTECTED] mailto:depley%40starband.net net wrote: I have a repeater receiver overload problem I am trying to cure. The repeater is a 900mhz 927.7125/902.7125. There is an FM broadcast station 100 yards away 104.9mhz. The repeater works fine at another site. My transmitter is a Motorola Purc 5000 running 75 watts the receiver is a converted maxtrac 800mhz radio. Duplexers are Telwave BpBr 4 cavity. I have 10 to 12 db degradation when plugged into 3 different antennas on the tower. When I use a 900mhz dish antenna pointed away from broadcast tower I only have 3 db degradation. I have tried 3 different maxtrac receivers, added 2 more BpBr cavities in the receiver side and used 3 pole filters in the receivers with no improvement. Today I looked at the signal level getting to the receiver at 104.9. To my surprise I was getting -8 dbm at the receiver. I believe this level is overloading the front end of my repeater. I was wondering if a stub cut for the broadcast frequency would work. Any thoughts would be greatly appreciated. David Epley, N9CZV Winchester, Indiana __ Be a better pen pal. Text or chat with friends inside Yahoo! Mail. See how. http://overview. http://overview. http://overview.mail.yahoo.com/ mail.yahoo.com/ mail.yahoo.com/
