[Repeater-Builder] Spectrum UHF Repeater SCR Crowbar circuit activating during TX
Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor. This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO
Re: [Repeater-Builder] Spectrum UHF Repeater SCR Crowbar circuit activating during TX
Could it be RF triggering the SCR? Jerry W9FS - Original Message - From: Ed To: Repeater-Builder@yahoogroups.com Sent: Thursday, October 15, 2009 9:17 AM Subject: [Repeater-Builder] Spectrum UHF Repeater SCR Crowbar circuit activating during TX Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor. This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO
[Repeater-Builder] Re: Spectrum UHF Repeater SCR Crowbar circuit activating during TX
A test you might try... find one or two fairly large (value) Electrolytic Capacitors as (or similar to the one already) installed in the power supply. With relatively short clip leads or decent wire, parallel one of the filter caps across the original Power Supply filter and if you have a second test cap, parallel it on the supply output. Then test to see if your crowbar trips. cheers, skipp --- In Repeater-Builder@yahoogroups.com, Ed ed.bathg...@... wrote: Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor. This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO
[Repeater-Builder] Re: Radio conversion to 225MHZ
Sometimes same amplifier used for VHF High-Band and UHF can be modified up/down to the 224 MHz band... but the conversion project is not for the faint of heart. In the case of the Micor PA... they are not an easy mod by any means and I was never able to get more than about 45% of the original rated power from some versions. The first problem is the frequency limit of the transistors, then modifying the substrate traces. One can retrofit replacement boards for the ceramic substrates (circuit boards used in the Micor and MSR-2000 RF Amplifiers) with the proper parts, but you're really building a new amplifier in place of the old. So why not start from scratch if it's a ground up project. I was able to get the UHF GE MVP amp to work quite well on 224 MHz, haven't yet had my hands in the Master Series Power Amplifier. That's a winter project... For the 224 MHz band... I've been building PA's from scratch and modified commercial gear. Lately it's been hard trying to find cheap enough power devices (transistors and fets) in any type of quantity. But I sometimes get luck on Ebay. What you end up with is mostly determined by the available drive level from your exciter (transmitter). cheers, s. --- In Repeater-Builder@yahoogroups.com, K5IN k...@... wrote: Kevin, Any suggestions for a decent quality 220mhz amp for repeater duty? Micor 20-25 watts drive or pull the PA and exciter in and 50-60 watts output? Thanks -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Kevin Custer Sent: Wednesday, October 14, 2009 5:57 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Radio conversion to 225MHZ J wrote: Has anyone converted any of the commercial (GE/Motorola) radios to the 220 band? If so what works and what doesnt. I need several 225 radios and thought this might be a route to go. I have converted MASTR II Mobiles, both multiplier and PLL exciter, with standard receivers to 220 MHz. - they work fine, the PLL is easier. There are preferred instructions on the MASTR II conversion site: http://www.repeater-builder.com/rbtip/geindex.html#220 http://www.repeater-builder.com/rbtip/geindex.html#220 For the M2 with a PLL exciter, Scott sells a complete conversion kit: http://www.repeater-builder.com/products/MIIconversionkit.html http://www.repeater-builder.com/products/MIIconversionkit.html The PA's won't convert, but there is an easy fix: http://www.repeater-builder.com/products/ampbd.html http://www.repeater-builder.com/products/ampbd.html I have converted MICOR Mobiles and Stations to 220 MHz. - they also work fine. There are preferred instructions on the MICOR conversion site: http://www.repeater-builder.com/rbtip/micor-index.html#220 http://www.repeater-builder.com/rbtip/micor-index.html#220 Helical Resonators modified for 220 operation are available here: http://www.repeater-builder.com/products/ http://www.repeater-builder.com/products/ The PA's won't convert, but again - never fear, the amp board is the solution: http://www.repeater-builder.com/products/ampbd.html http://www.repeater-builder.com/products/ampbd.html Any of the above radios can be converted to 220 MHz and achieve book specification sensitivity on the new band. My favorite is the MICOR. Hope this helps... Kevin Custer
[Repeater-Builder] HPN1000A Power Supply Schematic/Specs?
Hi All, That X9000 'consolette' didn't work with all the secure boxes stuff attached, but I removed the radio, control head added a standard cable, reprogrammed it, and it works. Anyway, the power supply that was inside is marked HPN 1000A. Anybody have a schematic or spec sheet on it? It looks pretty substantial. I saw the info on the Mitrek Consolette page in RB, but there weren't any specs on it. Thanks, Tim
[Repeater-Builder] Re: Radio conversion to 225MHZ
J and the Group, I have a converted MICOR mobile one 220 with a Toshiba amplifier module in it set to 15 W out driving a TE Systems 2206RN amplifier with 65 W out. In Skipps vault on Mt. Vaca and it has been working flawlessly since its installation, four years ago. The TE Systems, amplifier was not cheap, but when you take into account that I have not had to go up to the top of the amount in four years to work on it, it's a great deal. Gregory AC6VJ --- In Repeater-Builder@yahoogroups.com, K5IN k...@... wrote: Kevin, Any suggestions for a decent quality 220mhz amp for repeater duty? Micor 20-25 watts drive or pull the PA and exciter in and 50-60 watts output? Thanks -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Kevin Custer Sent: Wednesday, October 14, 2009 5:57 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Radio conversion to 225MHZ J wrote: Has anyone converted any of the commercial (GE/Motorola) radios to the 220 band? If so what works and what doesnt. I need several 225 radios and thought this might be a route to go. I have converted MASTR II Mobiles, both multiplier and PLL exciter, with standard receivers to 220 MHz. - they work fine, the PLL is easier. There are preferred instructions on the MASTR II conversion site: http://www.repeater-builder.com/rbtip/geindex.html#220 http://www.repeater-builder.com/rbtip/geindex.html#220 For the M2 with a PLL exciter, Scott sells a complete conversion kit: http://www.repeater-builder.com/products/MIIconversionkit.html http://www.repeater-builder.com/products/MIIconversionkit.html The PA's won't convert, but there is an easy fix: http://www.repeater-builder.com/products/ampbd.html http://www.repeater-builder.com/products/ampbd.html I have converted MICOR Mobiles and Stations to 220 MHz. - they also work fine. There are preferred instructions on the MICOR conversion site: http://www.repeater-builder.com/rbtip/micor-index.html#220 http://www.repeater-builder.com/rbtip/micor-index.html#220 Helical Resonators modified for 220 operation are available here: http://www.repeater-builder.com/products/ http://www.repeater-builder.com/products/ The PA's won't convert, but again - never fear, the amp board is the solution: http://www.repeater-builder.com/products/ampbd.html http://www.repeater-builder.com/products/ampbd.html Any of the above radios can be converted to 220 MHz and achieve book specification sensitivity on the new band. My favorite is the MICOR. Hope this helps... Kevin Custer
Re: [Repeater-Builder] Re: Spectrum UHF Repeater SCR Crowbar circuit activating during TX
Skipps idea sounds good to me. It's possible that the filter cap has gone bad. When the transmitter puts a load on the power supply, some AC ripple is getting through that trips the crowbar. 73, Joe, k1ike skipp025 wrote: A test you might try... find one or two fairly large (value) Electrolytic Capacitors as (or similar to the one already) installed in the power supply. With relatively short clip leads or decent wire, parallel one of the filter caps across the original Power Supply filter and if you have a second test cap, parallel it on the supply output. Then test to see if your crowbar trips. cheers, skipp
[Repeater-Builder] Need help
Am assisting in an estate (I'm an oldie that works CW on 160m so this is stuff is strange to me). Anyway, there is an antenna in the mess that we cannot identify. The SK was DEEP into VHF UHF (ran 2 repeaters just for him and XYL) so feel it is in that range. Heres the poop: (at least all we know): Total length: 11'6 LOA, of which 9' 6 is about 1/2-5/8OD fiberglass and 2' is a metal sleeve (where I would think a clamp to a mast would go. Its fed at the bottom by coax Only ID info on it is that is made by Antenna Specialists Co (can't find anything online on them) There is a possibility that in the lower area there might be a metal collar with 3 horizontal radials (ground plane)(such a gadget has turned up but we don't know where it belongs). Any help you guys can render will be greatly appreciated (especially any URL links to a picture catalog, freq's it covers, power rating, etc 73 Walt (N4GL)
Re: [Repeater-Builder] Need help
Walt, Please take a picture ans post it. We maybe able to identify it visually. Tim On 10/15/09, sjotrollet sjotrol...@yahoo.com wrote: Am assisting in an estate (I'm an oldie that works CW on 160m so this is stuff is strange to me). Anyway, there is an antenna in the mess that we cannot identify. The SK was DEEP into VHF UHF (ran 2 repeaters just for him and XYL) so feel it is in that range. Heres the poop: (at least all we know): Total length: 11'6 LOA, of which 9' 6 is about 1/2-5/8OD fiberglass and 2' is a metal sleeve (where I would think a clamp to a mast would go. Its fed at the bottom by coax Only ID info on it is that is made by Antenna Specialists Co (can't find anything online on them) There is a possibility that in the lower area there might be a metal collar with 3 horizontal radials (ground plane)(such a gadget has turned up but we don't know where it belongs). Any help you guys can render will be greatly appreciated (especially any URL links to a picture catalog, freq's it covers, power rating, etc 73 Walt (N4GL) -- Sent from my mobile device
Re: [Repeater-Builder] Need help
OK Tim, tks for the response. I'll probably be able to borrow a digital camera from my son and do so maybe next week. 73 Walt (N4GL) --- On Thu, 10/15/09, Tim Herron ki6...@gmail.com wrote: From: Tim Herron ki6...@gmail.com Subject: Re: [Repeater-Builder] Need help To: Repeater-Builder@yahoogroups.com Date: Thursday, October 15, 2009, 3:52 PM Walt, Please take a picture ans post it. We maybe able to identify it visually. Tim On 10/15/09, sjotrollet sjotrol...@yahoo. com wrote: Am assisting in an estate (I'm an oldie that works CW on 160m so this is stuff is strange to me). Anyway, there is an antenna in the mess that we cannot identify. The SK was DEEP into VHF UHF (ran 2 repeaters just for him and XYL) so feel it is in that range. Heres the poop: (at least all we know): Total length: 11'6 LOA, of which 9' 6 is about 1/2-5/8OD fiberglass and 2' is a metal sleeve (where I would think a clamp to a mast would go. Its fed at the bottom by coax Only ID info on it is that is made by Antenna Specialists Co (can't find anything online on them) There is a possibility that in the lower area there might be a metal collar with 3 horizontal radials (ground plane)(such a gadget has turned up but we don't know where it belongs). Any help you guys can render will be greatly appreciated (especially any URL links to a picture catalog, freq's it covers, power rating, etc 73 Walt (N4GL) -- Sent from my mobile device
Re: [Repeater-Builder] Need help
Hi Walt, Measure the radials of the ground plane, that might get you close. If there near about 6 inches then its UHF, if they are near around 15 to 18 then it would be in the VHF rage. But a picture could help some one spot it right away. Regards -Richard From: sjotrollet sjotrol...@yahoo.com To: Repeater-Builder@yahoogroups.com Sent: Thu, October 15, 2009 3:46:27 PM Subject: [Repeater-Builder] Need help Am assisting in an estate (I'm an oldie that works CW on 160m so this is stuff is strange to me). Anyway, there is an antenna in the mess that we cannot identify. The SK was DEEP into VHF UHF (ran 2 repeaters just for him and XYL) so feel it is in that range. Heres the poop: (at least all we know): Total length: 11'6 LOA, of which 9' 6 is about 1/2-5/8OD fiberglass and 2' is a metal sleeve (where I would think a clamp to a mast would go. Its fed at the bottom by coax Only ID info on it is that is made by Antenna Specialists Co (can't find anything online on them) There is a possibility that in the lower area there might be a metal collar with 3 horizontal radials (ground plane)(such a gadget has turned up but we don't know where it belongs). Any help you guys can render will be greatly appreciated (especially any URL links to a picture catalog, freq's it covers, power rating, etc 73 Walt (N4GL)
Re: [Repeater-Builder] Need help
The only Antenna Specialists antenna I could find that meets your description is a Base Commander Model ASP-680 series. There were 8 models covering from 146 to 174 MHz. The ASPA-680 covered from 146 to 149.5 MHz. This is a collinear antenna that has 3 dbd gain and was rated at 350 watts maximum. It does not have radials. Mounting clamps were not supplied with the antenna but were available as optional items. Hope this helps. As others have mentioned, a photo would really help confirm if this is a Base Commander or not. 73 Eric KH6CQ --- On Thu, 10/15/09, sjotrollet sjotrol...@yahoo.com wrote: From: sjotrollet sjotrol...@yahoo.com Subject: [Repeater-Builder] Need help To: Repeater-Builder@yahoogroups.com Date: Thursday, October 15, 2009, 9:46 AM Am assisting in an estate (I'm an oldie that works CW on 160m so this is stuff is strange to me). Anyway, there is an antenna in the mess that we cannot identify. The SK was DEEP into VHF UHF (ran 2 repeaters just for him and XYL) so feel it is in that range. Heres the poop: (at least all we know): Total length: 11'6 LOA, of which 9' 6 is about 1/2-5/8OD fiberglass and 2' is a metal sleeve (where I would think a clamp to a mast would go. Its fed at the bottom by coax Only ID info on it is that is made by Antenna Specialists Co (can't find anything online on them) There is a possibility that in the lower area there might be a metal collar with 3 horizontal radials (ground plane)(such a gadget has turned up but we don't know where it belongs). Any help you guys can render will be greatly appreciated (especially any URL links to a picture catalog, freq's it covers, power rating, etc 73 Walt (N4GL)
[Repeater-Builder] Re: Spectrum UHF Repeater SCR Crowbar circuit activating during TX
When the transmitter puts a load on the power supply, some AC ripple is getting through that trips the crowbar. 73, Joe, k1ike It could easily be any one of the electrolytics on the regulator board. I'd shotgun them all with new. I've seen this problem cured with new caps. Laryn K8TVZ
[Repeater-Builder] Maybe a strange question...
Our repeater is coordinated on a given two meter frequency. Due to terrain and other factors, we were forced to agree to some interference from a neighboring repeater, on the same frequency. The neighboring repeater is located on a peak roughly 100 miles away from us, and roughly 1800 feet higher in elevation. The repeater owner claims an ERP of 55 watts from an omni, however, I can consistently hear that repeater on my base at my QTH with an s-1 to s-3. I am transmitting 50w, 2dB loss in connectors, about 1.25 dB loss in feedline and about +6.5 dBi in antenna gain. So, I figure my ERP should be about 100 watts (+3dB = double in power, right). My antenna height is about 35 feet. So, as a newbie, I am assuming that if I can hear him at s-3, and he is transmitting 55w ERP, where my ERP is 100w, I should be able to program the radio with the proper offset and PL tone and get into the repeater. Is this a correct assumption? After all, if I can consistently hear him, the path is line of sight, right? Due to the difference in altitude, this would make sense. If all else is the same, I should be able to bring the repeater up. Or, is this repeater putting out much more than 55w ERP? Thanks!
[Repeater-Builder] Fw: OT Here is for old people with poor vision.....Your Guide to Nikon at Neuroscience
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RE: [Repeater-Builder] HPN1000A Power Supply Schematic/Specs?
Tim, The information is on page 47 of the manual here: www.repeater-builder.com/mitrek/pdfs/mitrek-super-consolette-station-manual -68p81040e80a.pdf 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Thursday, October 15, 2009 9:55 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] HPN1000A Power Supply Schematic/Specs? Hi All, That X9000 'consolette' didn't work with all the secure boxes stuff attached, but I removed the radio, control head added a standard cable, reprogrammed it, and it works. Anyway, the power supply that was inside is marked HPN 1000A. Anybody have a schematic or spec sheet on it? It looks pretty substantial. I saw the info on the Mitrek Consolette page in RB, but there weren't any specs on it. Thanks, Tim
Re: [Repeater-Builder] Maybe a strange question...
Your ERP will be around 55-60 watts given the info provided. I de-rated the dBi by 2 dB to give you dBd. I think that's correct. So your overall gain is only 1.25 dB. Chuck WB2EDV - Original Message - From: Randy Ross To: Repeater-Builder@yahoogroups.com Sent: Thursday, October 15, 2009 9:04 PM Subject: [Repeater-Builder] Maybe a strange question... Our repeater is coordinated on a given two meter frequency. Due to terrain and other factors, we were forced to agree to some interference from a neighboring repeater, on the same frequency. The neighboring repeater is located on a peak roughly 100 miles away from us, and roughly 1800 feet higher in elevation. The repeater owner claims an ERP of 55 watts from an omni, however, I can consistently hear that repeater on my base at my QTH with an s-1 to s-3. I am transmitting 50w, 2dB loss in connectors, about 1.25 dB loss in feedline and about +6.5 dBi in antenna gain. So, I figure my ERP should be about 100 watts (+3dB = double in power, right). My antenna height is about 35 feet. So, as a newbie, I am assuming that if I can hear him at s-3, and he is transmitting 55w ERP, where my ERP is 100w, I should be able to program the radio with the proper offset and PL tone and get into the repeater. Is this a correct assumption? After all, if I can consistently hear him, the path is line of sight, right? Due to the difference in altitude, this would make sense. If all else is the same, I should be able to bring the repeater up. Or, is this repeater putting out much more than 55w ERP? Thanks!
Re: [Repeater-Builder] Maybe a strange question...
--- On Thu, 10/15/09, Randy Ross rr...@librtynet.com wrote: From: Randy Ross rr...@librtynet.com Subject: [Repeater-Builder] Maybe a strange question... To: Repeater-Builder@yahoogroups.com Repeater-Builder@yahoogroups.com Date: Thursday, October 15, 2009, 9:04 PM Our repeater is coordinated on a given two meter frequency. Due to terrain and other factors, we were forced to agree to some interference from a neighboring repeater, on the same frequency. The neighboring repeater is located on a peak roughly 100 miles away from us, and roughly 1800 feet higher in elevation. The repeater owner claims an ERP of 55 watts from an omni, however, I can consistently hear that repeater on my base at my QTH with an s-1 to s-3. I am transmitting 50w, 2dB loss in connectors, about 1.25 dB loss in feedline and about +6.5 dBi in antenna gain. So, I figure my ERP should be about 100 watts (+3dB = double in power, right). My antenna height is about 35 feet. So, as a newbie, I am assuming that if I can hear him at s-3, and he is transmitting 55w ERP, where my ERP is 100w, I should be able to program the radio with the proper offset and PL tone and get into the repeater. Is this a correct assumption? After all, if I can consistently hear him, the path is line of sight, right? Due to the difference in altitude, this would make sense. If all else is the same, I should be able to bring the repeater up. Or, is this repeater putting out much more than 55w ERP? Unless you have a very good receiver and the repeater does not, if you can hear a repeater and your transmitter is running the same or more power, you should be able to bring it up. You normally assume that the repeater is using the same antenna for receiving and transmitting and the loss in the feedline and duplexer is the same for both.
[Repeater-Builder] Re: HPN1000A Power Supply Schematic/Specs?
Thanks Eric!!! Tim --- In Repeater-Builder@yahoogroups.com, Eric Lemmon wb6...@... wrote: Tim, The information is on page 47 of the manual here: www.repeater-builder.com/mitrek/pdfs/mitrek-super-consolette-station-manual -68p81040e80a.pdf 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Thursday, October 15, 2009 9:55 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] HPN1000A Power Supply Schematic/Specs? Hi All, That X9000 'consolette' didn't work with all the secure boxes stuff attached, but I removed the radio, control head added a standard cable, reprogrammed it, and it works. Anyway, the power supply that was inside is marked HPN 1000A. Anybody have a schematic or spec sheet on it? It looks pretty substantial. I saw the info on the Mitrek Consolette page in RB, but there weren't any specs on it. Thanks, Tim
Re: [Repeater-Builder] Spectrum UHF Repeater SCR Crowbar circuit activating during TX
I had a similar problem with a home brew supply. My fix was a choke (100 uHy)in series with the gate as close to the gate a possible. I bypassed the choke on both sides with 0.01 uF capacitors with leads as short as possible. This fixed my problem. You are probably rectifying RF inside the SCR. You might want to also bypass the anode of the SCR. Spectrum never was real good with engineering. YMMV 73 Glenn WB4UIV You might need to experiment with the values for the choke and capacitors. At 10:17 AM 10/15/2009, you wrote: Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor. This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO Yahoo! Groups Links
Re: [Repeater-Builder] Maybe a strange question...
Randy, it's pretty common these days for a transceiver in a valley to have much higher useful sensitivity than a receiver at a high repeater site, because your noise floor may be much lower, and the front end of the repeater's receiver may require much higher selectivity. It is also possible that the other repeater is running above its coordinated power level. I believe that many are. Such an accusation is usually unproductive. If you can still hear your own repeater over the distant one when both are active, that is NOT interference, that's users whining. CTCSS works both ways. Put it on your repeater's output, have users use decoders on their receivers, and *-poof-* problem solved. 73, Paul, AE4KR - Original Message - From: Randy Ross To: Repeater-Builder@yahoogroups.com Sent: Thursday, October 15, 2009 7:04 PM Subject: [Repeater-Builder] Maybe a strange question... If all else is the same, I should be able to bring the repeater up. Or, is this repeater putting out much more than 55w ERP? .
[Repeater-Builder] Re: Spectrum UHF Repeater SCR Crowbar circuit activating during TX
The paralleled Electrolytic caps into the power supply test I mentioned is a relatively easy test before one goes in for a mod. The Spectrum Crowbar Circuit was working and something obviously changed with age. Then I would focus my attention to the SCR Crowbar Circuit. Something not mentioned was... if the SCR circuit fired with the transmitter into a non-reactive load/termination (dummy load). s Glenn Little WB4UIV glennmaill...@... wrote: I had a similar problem with a home brew supply. My fix was a choke (100 uHy)in series with the gate as close to the gate a possible. I bypassed the choke on both sides with 0.01 uF capacitors with leads as short as possible. This fixed my problem. You are probably rectifying RF inside the SCR. You might want to also bypass the anode of the SCR. Spectrum never was real good with engineering. YMMV 73 Glenn WB4UIV You might need to experiment with the values for the choke and capacitors. At 10:17 AM 10/15/2009, you wrote: Having problems with a SPECTRUM 4000 UHF repeater that the voltage regulation works ok on RX, but when you kick it into TX, the SCR fires and blows the fuse or frys the resistor. This is the newer version power supply board that has the current limit control on it. We replaced the SCR and .25 ohm dump resistor, and it still triggers. I watched it trigger 2 times last night with a digital meter on the circuit and saw no overvoltage contition, at least not what the dmm registered. Theory: Could a bad cap be letting RF back into the crowbar circuit, causing the SCR to trigger from the RF rather then DC? Please Advise Ed N3SDO Yahoo! Groups Links
