[Repeater-Builder] Micor UHF PA control line question
Hi All, I have an application were I am using a 10 watt GM300 to drive a Micor 75 watt PA. I have a couple of concerns about this and I thought it would be better to ask the group than to blow up the PA and the GM300 (good idea, right?) I set the GM300 for 1.5 watts drive (Is 1.5 watts ok for a 0-10 watt GM300?) I connected the control line to A+ ( the book says 6-10 v, but I've told this is OK, I question that logic.) Keyed up, 105 watts! Turned GM300 to 1 watt, got 90, 3/4 watt got 80! OK, I'm blowing smoke, but I'm afraid of white smoke in cabinet! I would like to get this drive back to 1.5 -2 watts (protect the GM300 and prevent spurs) and get this PA back down to 70 watts Any easy way to control the control line? I'm missing something easy here, so flame suit is on! 73, Brian ** See what's new at http://www.aol.com
Re: [Repeater-Builder] Micor UHF PA control line question
A couple of ideas: 1. Build a simple voltage regulator capable of the current you need for the controlled stage. I think about a couple of amps, but you could insert an ammeter and actually measure it. Set your radio to 1.5 watts and then set the voltage to whatever gives you the desired output. 2. Build a 3 dB pad capable of 5 watts or better. The easiest way to do this is a coil of RG58 that is about 30 ft long. RG58 has about 1 dB per 10ft loss at 450MHz. Then you could set your radio to 2.5 watts out, and your amp would see 1.25 watts. Then attach your controlled line to 12v, and set your output power by the GM300 level. The GM300 should work fine at any level above a watt or so. Joe --- [EMAIL PROTECTED] wrote: Hi All, I have an application were I am using a 10 watt GM300 to drive a Micor 75 watt PA. I have a couple of concerns about this and I thought it would be better to ask the group than to blow up the PA and the GM300 (good idea, right?) I set the GM300 for 1.5 watts drive (Is 1.5 watts ok for a 0-10 watt GM300?) I connected the control line to A+ ( the book says 6-10 v, but I've told this is OK, I question that logic.) Keyed up, 105 watts! Turned GM300 to 1 watt, got 90, 3/4 watt got 80! OK, I'm blowing smoke, but I'm afraid of white smoke in cabinet! I would like to get this drive back to 1.5 -2 watts (protect the GM300 and prevent spurs) and get this PA back down to 70 watts Any easy way to control the control line? I'm missing something easy here, so flame suit is on! 73, Brian ** See what's new at http://www.aol.com Be a better sports nut! Let your teams follow you with Yahoo Mobile. Try it now. http://mobile.yahoo.com/sports;_ylt=At9_qDKvtAbMuh1G1SQtBI7ntAcJ
RE: [Repeater-Builder] Micor UHF PA control line question
OK, I'm blowing smoke, but I'm afraid of white smoke in cabinet! I would like to get this drive back to 1.5 -2 watts (protect the GM300 and prevent spurs) and get this PA back down to 70 watts Any easy way to control the control line? Why not skip the first two stages in the Micor amp and drive the driver stage with your GM300? Then you can just adjust the GM300's drive to get the final TPO you want. IIRC, the driver stage is normally around 8 watts input, 25 output, which then feeds the four finals in the 75 watt PA. Check the manual to confirm those power levels. Very important: there is NO HARMONIC FILTER in a UHF Micor PA - it's outboard in the antenna network within the Micor station chassis. If you're going to use that Micor PA standalone, put an isolator and a good low-pass filter on it. Along the same lines, keep in mind that the 75 watt rating is after the antenna network (isolator and harmonic filter); the PA's output is normally in the 90-95 watt range before the antenna network. --- Jeff
Re: [Repeater-Builder] Micor UHF PA control line question
On Nov 18, 2007, at 10:06 AM, [EMAIL PROTECTED] wrote: OK, I'm blowing smoke, but I'm afraid of white smoke in cabinet! I would like to get this drive back to 1.5 -2 watts (protect the GM300 and prevent spurs) and get this PA back down to 70 watts Someone mentioned making your own attenuator out of coax, but if you have a few bucks to put into it, in-line attenuators exist and make for a much cleaner installation... http://www.surplussales.com/RF/RFAtten-2.html That's just one example of sources for the things -- an online search for RF Attenuators yields a lot of vendors, some good some that obviously just jack up the prices and get them from somewhere else. YMMV. You just have to do some hunting to find the right values for amount of attenuation and the average power level the attenuator can handle, since the loss is all turned to heat. Inline attenuators also come in super-handy (as do tee connectors with variable coupling) for tuning up receivers and/or protecting a receiver from an overly aggressive pre-amp. :-) I see these things and hamfests and snatch them up, most people don't know what they're used for and/or don't know what they're worth, even on the used market... they're not always that cheap. I know, I know, everyone's got one of those I found this great deal at a hamfest stories... and not everyone can find that same deal. But it's definitely worth keeping your eyes open for these things as you start to build systems. You start to figure out what the hard or expensive components you MIGHT need are, and then you start to fill your basement with them -- and your wife just shakes her head and smiles, as long as you keep it all in the back corner where no one will see all of it. (GRIN!) Dayton often is the best place to shop, of course. I've only been to Dayton once, and saw so many things there I'd love to have handy back home just in case I needed it that I had a hard time not blowing the budget I had set aside for myself. Hunt the junk boxes at any hamfest you go to -- sometimes there are good deals on what are otherwise small and easy to lose parts like in- line attenuators, just waiting for you at the bottom of some guy's box full of utter junk. :-) -- Nate Duehr, WY0X [EMAIL PROTECTED]
RE: [Repeater-Builder] Micor UHF PA
Jeff you just gave away all the secrets... Good, concise job! Well, I've fixed more than a few. The Micor amps were a helluva lot more reliable and easier to service than the M2 UHF PA's ever were... --- Jeff
Re: [Repeater-Builder] Micor UHF PA
Thanks Guys Jim WK5Y - Original Message - From: Tom Parker To: Repeater-Builder@yahoogroups.com Sent: Monday, October 01, 2007 9:14 PM Subject: Re: [Repeater-Builder] Micor UHF PA Jeff you just gave away all the secrets... Good, concise job! Jeff DePolo wrote: The coupling cap between stages that is at the end of the semi-rigid coax can develop a bad connection as Tom said. Usually if it does, the pitting that occurs due to the arcing renders the cap's end plate too damaged to re-solder reliably, so replacing it is a good idea. The 25.5 pF caps across the collector-emitter can go bad. Usually this will manifest as somewhat-reduced output (depending on how many are bad), and/or power that jumps around. The little solder tabs that connect the RF ground on the substrates to DC ground along the top edge of the board will often develop bad connections and need to be re-flowed. When these open up you can have anything from low power out to spurs. The 0.01 uF DC decoupling caps that connect the output coax's shield to RF ground can go bad too, or develop a cold solder joint; usually these fail catastrophically so they're easy to spot. If you suspect a bad cap, sometimes you can locate the bad one by applying a little pressure with an insulated tuning tool while the transmitter is on. You might get lucky and catch it arcing as it makes and breaks the connection. Last but not least, a cracked ceramic substrate will cause all kinds of grief if the groundplane (underside of the substrate) breaks. A crack in the substrate itself isn't a problem, but if the copper cracks along with it, scrap it. --- Jeff -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jim Russell Sent: Sunday, September 30, 2007 9:08 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Micor UHF PA Thanks Jim WK5Y - Original Message - From: Tom Parker mailto:[EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sunday, September 30, 2007 2:25 PM Subject: Re: [Repeater-Builder] Micor UHF PA Also check the 52 pf coupling capacitors between each amp stage. We see these go bad and intermitten from time to time. Still too cheap not to replace, but sometimes all they need is a little heat and solder reflow. thp Milt wrote: Jim, You might be thinking about the 33pf(? value) on the collector/emitter junction on the flat pack RF transistors. Or the leaching problem that is mentioned in the service manual. I always replaced the chip caps on the base/emitter and collector/emitter junctions when we had to replace a defective transistor. There were PK-xxx packages for replacing the lower level transistors that included the transistor, chip caps and solder. Milt N3LTQ - Original Message - From: Jim Russell mailto:[EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Friday, September 28, 2007 11:24 PM Subject: [Repeater-Builder] Micor UHF PA Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.13.35/1039 - Release Date: 9/29/2007 9:46 PM Internal Virus Database is out-of-date. Checked by AVG Free Edition. Version: 7.5.487 / Virus Database: 269.13.27/1020 - Release Date: 9/20/2007 12:07 PM No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.13.37/1042 - Release Date: 10/1/2007 6:59 PM
Re: [Repeater-Builder] Micor UHF PA
Thanks Jim WK5Y - Original Message - From: Tom Parker To: Repeater-Builder@yahoogroups.com Sent: Sunday, September 30, 2007 2:25 PM Subject: Re: [Repeater-Builder] Micor UHF PA Also check the 52 pf coupling capacitors between each amp stage. We see these go bad and intermitten from time to time. Still too cheap not to replace, but sometimes all they need is a little heat and solder reflow. thp Milt wrote: Jim, You might be thinking about the 33pf(? value) on the collector/emitter junction on the flat pack RF transistors. Or the leaching problem that is mentioned in the service manual. I always replaced the chip caps on the base/emitter and collector/emitter junctions when we had to replace a defective transistor. There were PK-xxx packages for replacing the lower level transistors that included the transistor, chip caps and solder. Milt N3LTQ - Original Message - From: Jim Russell To: Repeater-Builder@yahoogroups.com Sent: Friday, September 28, 2007 11:24 PM Subject: [Repeater-Builder] Micor UHF PA Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.13.35/1039 - Release Date: 9/29/2007 9:46 PM
RE: [Repeater-Builder] Micor UHF PA
The coupling cap between stages that is at the end of the semi-rigid coax can develop a bad connection as Tom said. Usually if it does, the pitting that occurs due to the arcing renders the cap's end plate too damaged to re-solder reliably, so replacing it is a good idea. The 25.5 pF caps across the collector-emitter can go bad. Usually this will manifest as somewhat-reduced output (depending on how many are bad), and/or power that jumps around. The little solder tabs that connect the RF ground on the substrates to DC ground along the top edge of the board will often develop bad connections and need to be re-flowed. When these open up you can have anything from low power out to spurs. The 0.01 uF DC decoupling caps that connect the output coax's shield to RF ground can go bad too, or develop a cold solder joint; usually these fail catastrophically so they're easy to spot. If you suspect a bad cap, sometimes you can locate the bad one by applying a little pressure with an insulated tuning tool while the transmitter is on. You might get lucky and catch it arcing as it makes and breaks the connection. Last but not least, a cracked ceramic substrate will cause all kinds of grief if the groundplane (underside of the substrate) breaks. A crack in the substrate itself isn't a problem, but if the copper cracks along with it, scrap it. --- Jeff -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Jim Russell Sent: Sunday, September 30, 2007 9:08 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Micor UHF PA Thanks Jim WK5Y - Original Message - From: Tom Parker mailto:[EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Sunday, September 30, 2007 2:25 PM Subject: Re: [Repeater-Builder] Micor UHF PA Also check the 52 pf coupling capacitors between each amp stage. We see these go bad and intermitten from time to time. Still too cheap not to replace, but sometimes all they need is a little heat and solder reflow. thp Milt wrote: Jim, You might be thinking about the 33pf(? value) on the collector/emitter junction on the flat pack RF transistors. Or the leaching problem that is mentioned in the service manual. I always replaced the chip caps on the base/emitter and collector/emitter junctions when we had to replace a defective transistor. There were PK-xxx packages for replacing the lower level transistors that included the transistor, chip caps and solder. Milt N3LTQ - Original Message - From: Jim Russell mailto:[EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Friday, September 28, 2007 11:24 PM Subject: [Repeater-Builder] Micor UHF PA Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.13.35/1039 - Release Date: 9/29/2007 9:46 PM Internal Virus Database is out-of-date. Checked by AVG Free Edition. Version: 7.5.487 / Virus Database: 269.13.27/1020 - Release Date: 9/20/2007 12:07 PM
[Repeater-Builder] Micor UHF PA
Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y
Re: [Repeater-Builder] Micor UHF PA
Jim, You might be thinking about the 33pf(? value) on the collector/emitter junction on the flat pack RF transistors. Or the leaching problem that is mentioned in the service manual. I always replaced the chip caps on the base/emitter and collector/emitter junctions when we had to replace a defective transistor. There were PK-xxx packages for replacing the lower level transistors that included the transistor, chip caps and solder. Milt N3LTQ - Original Message - From: Jim Russell To: Repeater-Builder@yahoogroups.com Sent: Friday, September 28, 2007 11:24 PM Subject: [Repeater-Builder] Micor UHF PA Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y
Re: [Repeater-Builder] Micor UHF PA
Also check the 52 pf coupling capacitors between each amp stage. We see these go bad and intermitten from time to time. Still too cheap not to replace, but sometimes all they need is a little heat and solder reflow. thp Milt wrote: Jim, You might be thinking about the 33pf(? value) on the collector/emitter junction on the flat pack RF transistors. Or the leaching problem that is mentioned in the service manual. I always replaced the chip caps on the base/emitter and collector/emitter junctions when we had to replace a defective transistor. There were PK-xxx packages for replacing the lower level transistors that included the transistor, chip caps and solder. Milt N3LTQ - Original Message - From: Jim Russell mailto:[EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Friday, September 28, 2007 11:24 PM Subject: [Repeater-Builder] Micor UHF PA Ok guys help this old man out. I worked in a Motorola Shop back in the 80's. I seem to remember a problem with Micor UHF PA's where the solder connection on a perticular chip capacitor would go bad causing the power to drop to next to nothing. I think the solution was to resolder the cap with silver solder. Do any of you know of a better solution. I have one of the animals acting intermittant. Jim WK5Y No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.488 / Virus Database: 269.13.35/1039 - Release Date: 9/29/2007 9:46 PM
