Re: [time-nuts] COMPLETELY off topic - but I know you'll read itanyway.
Jim, Ahh audio, my first love and almost 50-years of experience. You already have replies with the right answers but here is my 2-cents.. >I've dug out the manual and even though the specifications say it can do 4 >ohms in bridged mode, there is another statement that says it doesn't >recommend it. The recommendation is due to current limiting in the amplifier. The amplifier output impedance is doubled from the typical 4-ohm per channel to 8-ohm when bridged. If you loaded the bridged output with 4-ohm (both 8-ohm speakers in parallel), it would require double the current through each output stage in addition to 2x the draw from the power supply. Current limiting, probably in the power supply, would result at a much lower peak voltage from each channel. The result is less power (earlier clipping/distortion) with this lower than design point load. >"The A channel handles the positive voltage and the B channel becomes the >negative, thus doubling the output voltage swing." This is a very odd way to state what's happening in the bridged mode. You gatta love manuals written by the marketing department. Not totally wrong but only accurate during complex instances in time when the positive half of the output is indeed handled by ch-A and the negative by ch-B. In another instance however, this will be reversed. A more accurate description is what someone else has already stated as a push-pull arrangement of the out-of-phase driven channels. The bridge mode switch couples one of the input channels to both output stages but also inserts an additional op-amp stage (phase inverter) in only one of the channels. Now as the input signal goes positive, the "hot" terminal of ch-A will be driven positive while the "hot" terminal of ch-B will be driven negative equally. All this reverses as the input signal goes negative. The clincher for you to NOT operate in bridge mode is that you have TWO speakers of the correct impedance to match each channel separately. Just drive both input channels with a Y adapter from your mono source and you will have the best arrangement. If there is ever a time that you want to only drive one of the 8-ohm speakers, now you would want to bridge the amp and connect the one speaker accordingly. Regards... Don - Original Message - From: Jim Palfreyman To: Discussion of precise time and frequency measurement Sent: Saturday, October 11, 2008 7:48 AM Subject: Re: [time-nuts] COMPLETELY off topic - but I know you'll read itanyway. Thanks folks for your quick replies. I've dug out the manual and even though the specifications say it can do 4 ohms in bridged mode, there is another statement that says it doesn't recommend it. Here is what it says about bridged mode: "The A channel handles the positive voltage and the B channel becomes the negative, thus doubling the output voltage swing." Needless to say, Poul's comment regarding running them as two separate channels because if one fails I'll have another as a spare is the clincher for me. Being from an IT background - backup is all important. Thanks folks! 2008/10/11 Javier Herrero <[EMAIL PROTECTED]> > If 500W are specified for a 4 ohm load, you will only obtain 250W for > each channel over a 8 ohm speaker. In bridged mode, it is not true that > basically one channel drives the upper part of the sine and the other > the lower: they operate in push-pull, supplying each side of the speaker > with opposite phases so you will obtain the double peak-to-peak voltage > value over the load than in the single ended configuration. Double > voltage would mean four-times power, so the amplifier surely is not > rated for the same load in bridged mode than in single-ended two-channel > mode. If minimum load for each channel is 4 ohm in single-ended mode, > usually it is 8 ohm for two channels in bridged mode. > > So if you have 8 ohm speakers... use it in single ended mode (better > reliability also, as Poul-Henning pointed), and you will get 250W per > channel. In brigde mode, you could only put the two speakers in parallel > if the amplifier is rated for 4 ohm loads in bridged mode. > > Regards, > > Javier > > Jim Palfreyman escribió: > > OK I have an interesting but simple problem that has nothing to do with > > time. But I'm sure someone on this list will know. And besides I can't be > > stuffed finding another list with such a good S/N ratio. > > > > In my spare time I play in a band. > > > > I have a 1000W amplifier that can be either two 500W stereo channels or a > > single 1000W mono running in "bridged" mode. (Basically one channel > > amplifies the upper part of the sine curve and the other the lower.) > > > > The amp can drive speakers down to 4 ohms. > > > > I have two 8 ohm speakers. > > > > The source is mono. > > > > Do I run each 8 ohm speaker on its own 500W chan
Re: [time-nuts] Austron 2000C on EBay
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY What is the frequency source in this unit? Regards... Don - Original Message From: Rob Kimberley <[EMAIL PROTECTED]> To: Discussion of precise time and frequency measurement Sent: Wednesday, October 3, 2007 12:07:02 PM Subject: [time-nuts] Austron 2000C on EBay ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Just spotted Item 280158942374. Just wondered why they only took picture of the rear. Rob Kimberley ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Fury OEM GPSDO board
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Said, Please add my name to the list for the Fury board. I will make PayPal payment after details from you. Thanks... Don Johnson - Original Message - From: [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Sunday, September 30, 2007 7:22 PM Subject: [time-nuts] Fury OEM GPSDO board Hi guys, ok, we have enough interest, and I cleared the project with marketing. We can offer the units new with warranty for $550 each to Time Nuts members. So far I have the following members noted: Ernie Scott John Matt Brian Please let me know if there is additional interest. We can ship the units throughout the next week. We can accept PayPal (preferred), US checks, or wire-transfers. I will get in touch with you offline about payment details. Since not all OCXO's and oscillators that are out there may work with the Fury really well, we will give a functional return warranty (units need to be clean, un-modified and in working order to be returned). Shipping cannot be refunded. Please see the attached image for what you will receive: the PCB with SMA connectors for 10MHz input and the EFC output, and an adapter cable for the M12+ GPS antenna to BNC. No OCXO is included. The external OCXO can also be powered from the unit (at 10.45V with 250mA max current, most 12V OCXO's will run well at 10.45V) - that has the advantage of the unit being able to offer temperature compensation for OCXO's that have a linear temperature-to-current relationship. The Fury expects a 10MHz Sine or CMOS output from the OCXO and will work between 0dBm and +10dBm. The Fury will generate 0V to +5V EFC voltage. It runs from a 11.0V to 14.0V clean external DC supply. An LCD (16x2) and a single-key button can optionally be connected for status information. The 10MHz from the OCXO will be buffered (emitter-follower without gain) and is available as a low-pass filtered, buffered Sine Wave output and also as a fast-slew-rate 50 Ohm compatible CMOS output. Thanks for your interest everyone, Said ** See what's new at http://www.aol.com -- -- ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Another GPSDO project
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi group, I an still somewhat in the middle of this project but what's left is mostly fine tuning and the cosmetics of getting it enclosed. I have been using a Trimble Thunderbolt for over a year now and, for the most part, find it a very nice long term comparative reference for my Efratom Rb. I purchased this Thunderbolt as a Starter kit that included the antenna and downlead on eBay and like the overall performance. The weakest part however, of the TB is the oscillator. With room temperature cycling with heating and AC, I would typically see a +-20 nS sine wave looking steering pattern with a period of about 10-20 minutes. I always wanted to modify my unit to use a better doubled ovenized oscillator. Recently, George Dubovsky offered some Trimble Thunderbolts (boards only) for sale and I jumped at the chance to use one of his boards as an experimental set up and not mess up my only GPS reference. Some of you may know, the TB board is made to solder SMB connectors for an external oscillator. These connector pads are useable only after you remove the onboard oscillator. There is one for the 10Mhz in and another for the VFC out. The electrical characteristics nicely match an HP 10811 and that's what I used. Using Thunderbolt Monitor software, the VFC slope was modified from -5.00 to -0.45 Hz/V and the Filter TC and Damping were changed to 400 and 1.1 respectively to more gently steer the 10811. The results seem to be working great. I now have a very gentle 40-minute, +- 5 nS pattern as referenced to my local Rb. I am using the more stable and low phase noise 10811-80168 so I didn't compromise on the low phase noise of the original onboard oscillator but greatly improved stability. I am still working with filter TC and damping settings to see if further improvement can be had. The trick seems to be very gentle nudges without over steering on one side or "loosing it" on the other. I would also like to experiment with the Fury board with an external oscillator to compare results. Are you listening Said? Regards... Don ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Antenna recommendation for Timing Amateur
Jim, You may not have to have an amplified antenna but it will work best by providing stronger signals thus allowing more SV to be tracked at any given time. This would be especially true during heavy rain periods. The primary difference between a timing antenna and anything otherwise is a design that limits reception path length differences at all elevations and azimuths. The physical appearance of a timing antenna is usually a bullet shape or small dome compared to a big square. The precise point in the antenna that provides the highest SNR to all of the currently received SVs at any elevation and azimuth is where the timing phase differences are determined. Any difference in this being a single precise point vs. multiple points that move around within the antenna’s gain pattern would define the antenna’s phase error. Don J. True-Cal Services - Original Message From: Jim Miller <[EMAIL PROTECTED]> To: time-nuts Sent: Thursday, June 14, 2007 11:11:43 AM Subject: [time-nuts] Antenna recommendation for Timing Amateur I'm planning on getting a M12M and would like a recommendation for an antenna for timing purposes. I'm just an amateur looking to discipline an oscillator. No scientific uses planned. My antenna coax is likely to be 30ft or more so I suspect I'll need an amplified antenna. The M12M outputs 3v so the "timing" antennas offered by Synergy don't directly apply. What is the real difference between a "timing" antenna and one meant for mobile use? Synergy offers several amplified mobile antennas that would work with 3v. tia jim ab3cv ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
Re: [time-nuts] Information on OVCXO (Don J)
> I just become the owner of a Precision Crystal EROS-750- SBR -4 > voltage controlled OCXO. I believe that this is the oscillator that > is used in the SRS SR620 Frequency Counter when it has the 2-ppb > option-01 timebase (please correct me if wrong info). The unit has > four terminals simply labled 1-4 on the bottom as well as the case > studs. The label says it is a +15VDC unit. Can anyone provide the > pin-out of this oscillator. Short of an actual pin diagram, can > anyone suggest a way to help identify each pin function, i.e. DC > resistance, AC impedance, safely applying power with series > resistance? I do not want to blow this unit as I have high hopes for > it as a replacement disciplined oscillator in my Trimble Thunderbolt > GPS timebase. I will be glad to share my conversion experience as I > proceed with this project. Thanks in advance for any help. > > Don Johnson > True-Cal Services *** So what happened to the original oscillator, Don? DaveB, NZ Hi Dave, I guess you are asking about the original oscillator in the Thunderbolt. The symptoms would suggest that the heater has gone bad. I use it to track my Rb standard for long term drift. I use an SRS SR620 with a Tek display to watch Alan Variance and drift over both short and long time intervals. I monitor the rate of time change between ch-A (Rb) and ch-B (Thunderbolt) 10MHz signals as they cross through 0.0V trigger point. The Thunderbolt has started to do a rapid change of >100 ns as my air conditioning cycles in the room. The Thunderbolt monitor computer interface program displays only 0.5 degree change in internal temperature. In the past, I could always maintain <20 ns change that resembled a sine wave with about a 5-minute period (GPS disciplined TC) with little affect from the room AC. Now it looks like a sawtooth with the period of my AC. The original oscillator is an OCXO but not as good as this new double ovened SC-cut oscillator. The VC range is the same between the two oscillators and the time-constant I can change with the Thunderbolt software. Comments… Regards… Don time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
[time-nuts] Information on OVCXO
Hello Time-Nuts, I just become the owner of a Precision Crystal EROS-750- SBR -4 voltage controlled OCXO. I believe that this is the oscillator that is used in the SRS SR620 Frequency Counter when it has the 2-ppb option-01 timebase (please correct me if wrong info). The unit has four terminals simply labled 1-4 on the bottom as well as the case studs. The label says it is a +15VDC unit. Can anyone provide the pin-out of this oscillator. Short of an actual pin diagram, can anyone suggest a way to help identify each pin function, i.e. DC resistance, AC impedance, safely applying power with series resistance? I do not want to blow this unit as I have high hopes for it as a replacement disciplined oscillator in my Trimble Thunderbolt GPS timebase. I will be glad to share my conversion experience as I proceed with this project. Thanks in advance for any help. Don Johnson True-Cal Services ___ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
