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Jason <jayson1@stiger.com>: May 17 07:10PM -0400 I just picked up a small spectrum analyzer to check out some transceivers I have. They are 10 meter ham units and put out anywhere from 4-12 watts @ 50 ohms. The new spectrum analyzer can handle a maximum of 10 dbm. What size voltage divider would I need to reduce the transceiver wattage to less than the 10 dbm for the analyzer? Thanks.

Rheilly Phoull <rheilly@bigslong.com>: May 18 08:19AM +0800 On 18/05/2021 7:10 am, Jason wrote: > from 4-12 watts @ 50 ohms.  The new spectrum analyzer can handle a > maximum of 10 dbm.  What size voltage divider would I need to reduce the > transceiver wattage to less than the 10 dbm for the analyzer?  Thanks.   You should be looking at the voltages of the tx outputs rather than the power.

dplatt@coop.radagast.org (Dave Platt): May 17 06:47PM -0700 >from 4-12 watts @ 50 ohms. The new spectrum analyzer can handle a >maximum of 10 dbm. What size voltage divider would I need to reduce the >transceiver wattage to less than the 10 dbm for the analyzer? Thanks.   1 watt is 30 dBm. 4 watts would be 36 dBm. 12 watts would be about 41 dBm.   In order to avoid driving the spectrum analyzer into overload, I'd suggest keeping the input signal at about 1 milliwatt (0 dBm). This will also give you some safety margin to avoid exceeding the 10 dBm limit.   40 dB of attenuation would take you down from 12 watts, to 1.2 milliwatts, so that's a good figure to shoot for.   So, you'd want either one 40 dB attenuator, or two 20 dB attenuators in series. Make sure that the attenuator is rated to handle the full output of the transmitter, or you'll cook it.   A single 30 dB attenuator would keep you under your 10 dBm worst-case limit if you feed it with 4 watts, but you'd be a hair over the limit at 12 watts. So, I'd stick with 40 dB of attenuation.   Make sure these are 50-ohm attenuators, of course, since that's what the transmitters will expect (and want) to see.

Ralph Mowery <rmowery42@charter.net>: May 17 11:25PM -0400 In article <kuibnh-38h.ln1@coop.radagast.org>, dplatt@coop.radagast.org says... > at 12 watts. So, I'd stick with 40 dB of attenuation.   > Make sure these are 50-ohm attenuators, of course, since that's what > the transmitters will expect (and want) to see.   To add to that, you probalby want to allow another 20 to 50 db so you have plenty of head room so as not to over drive the SA and see spurious signals.   A short antenna on the SA would probalby give enough signal to see what is needed.

Phil Allison <pallison49@gmail.com>: May 17 10:49PM -0700 Ralph Mowery wrote: ---------------------------------   > A short antenna on the SA would probalby give enough signal to see what > is needed.   ** Best a safest answer & "short" = about 100mm.   Either that or a single loop around the co-ax feeding a dummy load.   The SA needs to see about 100mV at 30MHz to stay clear of spuriae.     ..... Phil

Jason <jayson1@stiger.com>: May 18 09:02AM -0400 On 5/18/21 1:49 AM, Phil Allison wrote:   > Either that or a single loop around the co-ax feeding a dummy load.   > The SA needs to see about 100mV at 30MHz to stay clear of spuriae.   > ..... Phil   Tried the loop around the coax, just a prior loop I had made up one time for RG-8 (this is RG-58 I'm using now). It's not tight around the RG-58 of course, but output stays well within the analyzer limit. However, harmonics vary depending on where I move the loop. Maybe I should make a tight single loop around the coax?

Jason <jayson1@stiger.com>: May 18 12:06PM -0400 On 5/18/21 9:02 AM, Jason wrote: > of course, but output stays well within the analyzer limit.  However, > harmonics vary depending on where I move the loop.  Maybe I should make > a tight single loop around the coax?   Ok, as I already had a 20:1 voltage divider, which brought levels down to 10 dbm, I simply added another one in series. I've been testing out a TinySA handheld unit about the size of a cigarette pack. After watching some videos on it, it is recommended to keep levels at -30 dbm to prevent false spurs and harmonics. My voltage divider added in series does just that at just under -40 dbm.   Here's a question I can't seem to find the answer to: what are the harmonic emission requirements for spectral purity for HF radio transceivers in the US? I *think* its either -30 or -40db below, but it's been years since I've used these transceivers. Thanks.

T i m <news@spaced.me.uk>: May 17 09:11PM +0100 On Mon, 17 May 2021 11:00:05 -0400, legg <legg@nospam.magma.ca> wrote:   <snip>     >>Rear >>https://ibb.co/w6Wq6hj   >You're running at 220V? OK   Check.   >Make sure the choke ends aren't touching as they leave the toroid >center.   Do you mean the opposite ends RL, in as it passes past out? If so, no they seem to be a good 2mm apart.   https://ibb.co/YQg7Lp4   > Wires not shorting to core.   Measurable just with my DMM? (if so, I can't measure anything).   >No sign of cracked cores.   Do I only have one on the board (the big one in the final stage (is it?)) and if so, not that I can easily see?   >Check big primary bulk electros - voltages should be roughly >equal   I was inspecting those earlier and noted the caps were spanning an 'island' and each cap only 200V (so in series where the working voltages add)?   >with small low-frequency ripple.   Would AC volts on my DMM be ok for that RL (I do have a USB scope but I wouldn't want to use it on mains and I haven't modded it to be AC coupled yet).   >Replace small electros on primary side,   The ones near C18? (just for reference, C16 is 100uF, 25V and C17 is 4.7uF, 50V). I have one of those automatic component testers. Would an 'ok' from one of those be ok?   >then optocoupler.   An EL817. [1] (there is a TL431A (voltage reg?) beside the opto FWIW).     >A basic forward converter.   I agree it doesn't look 'overpopulated' as such (thank goodness!). ;-)   >Integrated primary switch should >be replaceable,   Is that 5 legged device on the underside?   > but check transformer Lp first.   Sorry, you have lost me on that one. ;-(   Cheers, T i m   [1] When I was a datacomms guy we used to make and sell a Current loop 'Line driver' that used an opto for the receiver. They would often be sent back marked as faulty, we would bench test them and loop the output back to the input and they would often pass (BERT). Heat, cool, tapping, still ok. Then I designed and built a small box where we could vary the input current to better represent true line (loss) conditions and lo-and-behold, some of those that were NFF now failed because their sensitivity had dropped, putting the sense threshold right near the TX current level. We found a new opto would trigger at around 10mA, the max current from the TX was 20mA and some of these returned 'faulty' ones were nearer 18. I had to build testers for all the techs. ;-)

T i m <news@spaced.me.uk>: May 17 09:22PM +0100 On Mon, 17 May 2021 11:00:05 -0400, legg <legg@nospam.magma.ca> wrote:   <snip>   >Check big primary bulk electros - voltages should be roughly >equal with small low-frequency ripple.   166V across each, no real measurable ripple (off load of course).   Cheers, T i m

Chuck <chuck23@dejanews.net>: May 17 03:47PM -0500 >around 10mA, the max current from the TX was 20mA and some of these >returned 'faulty' ones were nearer 18. I had to build testers for all >the techs. ;-) To test C16 and 17 you would need an ESR tester. It is a pretty good bet that both are bad. Make sure that you use 105C caps.

whit3rd <whit3rd@gmail.com>: May 17 03:43PM -0700 On Sunday, May 16, 2021 at 5:38:56 PM UTC-7, T i m wrote: > 4 x 1000uF, 16V) on the output / smoothing stage, so replaced all 4. > Alas (and sorta as expected), it didn't really help   > I assume the 3 legged device on the LV side is a switching transistor   TNo, that has to be the low-voltage rectifier (if it really IS rated for 20A, it has to be heatsinked); if it's leaky it would be a quasi-short-circuit, and that will deliver AC to the capacitors you replaced, which would kill 'em soonish.   That's the likely culprit, probably will need to be desoldered to find the part number, and will be easy-ish to test. Sometimes there's two diodes, center pin common, in this form factor.

T i m <news@spaced.me.uk>: May 18 10:15AM +0100 On Mon, 17 May 2021 15:47:30 -0500, Chuck <chuck23@dejanews.net> wrote:   <snip>     >>The ones near C18? (just for reference, C16 is 100uF, 25V and C17 is >>4.7uF, 50V). I have one of those automatic component testers. Would an >>'ok' from one of those be ok?   <snip>   >To test C16 and 17 you would need an ESR tester.   Yes, I have one. Of the 4 x 1000uF smoothing caps across the output (where one had blown) 3 had an ESR around 0.1 and the blown one a touch higher? Is that right / normal (FWIW they also showed a Vloss of ~2% and were all around 1100uF)? [1]   >It is a pretty good >bet that both are bad.   Ok, I'll pull test / replace those next.   >Make sure that you use 105C caps.   Check (I did so with the 4 smoothing caps, but didn't check the lead spacing on my order (doh)).   Cheers, T i m   [1] Could it be bulging because it just happened to be the closest to the output choke and that had been running fairly hot, rather than it had failed by drying out or whatever? (they were nichicon 105 1000uF 16V YV(M) H1305)

T i m <news@spaced.me.uk>: May 18 10:27AM +0100 On Mon, 17 May 2021 15:43:12 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:     >> I assume the 3 legged device on the LV side is a switching transistor   >TNo, that has to be the low-voltage rectifier (if it really IS rated for 20A, it has to >be heatsinked);   The two TO(xxx?) packaged devices under the board were bolted to the square U section case with insulators. eg, the whole ally plate chassis and perforated ally 'lid' would be a heatsink.   OOI, as it seems this PCB was originally designed to be 5V / 40A, so is it likely they would have used the same component there for 12V / 20A (I know it has to dissipate the same number of watts but wondered if it might be able to handle 20A easier if it was originally specced to take 40A)?   > if it's leaky it would be a quasi-short-circuit, and that will deliver >AC to the capacitors you replaced, which would kill 'em soonish.   Ah. ;-(   >That's the likely culprit, probably will need to be desoldered to find the part >number, and will be easy-ish to test.   Understood.   >Sometimes there's two diodes, center >pin common, in this form factor.   Yes, I think I've seen such on the various SMPSU diagrams I've been checking. ;-)   As advised elsewhere, I think I'll pull and test (and possibly replace *anyway*) the two small electrolytics first and then move to the rectifier.   FWIW, I do read around 10V DC on the output but it's fluctuating. I could put my PC digiscope on it (after checking the output for AC on my DMM)?

legg <legg@nospam.magma.ca>: May 18 09:33AM -0400 >Do you mean the opposite ends RL, in as it passes past out? If so, no >they seem to be a good 2mm apart.   >https://ibb.co/YQg7Lp4   The wires without magnet wire enamel look pretty close to me. You should be concerned that wires exiting core in different directions are not visibly or physically separated. Force these apart with a flat screw driver and insert biz card thick paper stock.   >> Wires not shorting to core.   >Measurable just with my DMM? (if so, I can't measure anything).   You're looking for discoloration, crumbling of core where magnet wires are forced against core edges due to winding force. Discoloration is sign of point-contact heating.   >>No sign of cracked cores.   >Do I only have one on the board (the big one in the final stage (is >it?)) and if so, not that I can easily see?   If you don't hear grinding noise or see shifting, when manipulated, then there's probably no issue.   >Would AC volts on my DMM be ok for that RL (I do have a USB scope but >I wouldn't want to use it on mains and I haven't modded it to be AC >coupled yet).   Your later description sound like these are OK. Large voltage imbalance or large ripple would indicate failure of one or both.   >Is that 5 legged device on the underside?   >> but check transformer Lp first.   >Sorry, you have lost me on that one. ;-(   Main transformer primary inductance of a forward converter running off mains will be more than 400uH - typically 2mH.   Lower values suggest shorting of windings or terminal connections/traces.   RL

John Crane <john_crane_59@yahoo.com>: May 18 06:49AM -0500 Can anyone point me to documentation or schematics for this? I have one in pristine condition, until last month when a capacitor blew...   Turns out these use the problematic Astec power supplies identical to the ones used in the Osborne 01. There is a 0.1uF 250V polymer cap that tends to blow. In fact, I've had 2 Osborne 01 machines that blew while in service - smoke and all. I replaced the cap and now they work perfectly.   The Westwind, on the other hand, will not recognize the hard disk. However the built-in ramdisk does work.   My fear is that when the cap blew, a voltage transient may have taken out one or more of the large Shugart VLSI chips on the disk controller board. These chips may be difficult to source these days.   -John

John Crane <john_crane_59@yahoo.com>: May 18 07:07AM -0500 Can anyone point me to documentation or schematics for this? I have one in pristine condition, until last month when a capacitor blew...   Turns out these use the problematic Astec power supplies identical to the ones used in the Osborne 01. There is a 0.1uF 250V polymer cap that tends to blow. In fact, I've had 2 Osborne 01 machines that blew while in service. I replaced the cap and now they work perfectly.   The Westwind, on the other hand, will not recognize the hard disk. However the built-in ramdisk does work.   My fear is that when the cap blew, a voltage transient may have taken out one or more of the large Shugart VLSI chips on the disk controller board. These chips may be difficult to source these days.   -John

Tim R <timothy42b@aol.com>: May 17 04:38PM -0700 On Saturday, May 15, 2021 at 8:35:05 PM UTC-4, Bennett Price wrote: > > Good luck   > Similar but even cheaper and for $5.00 worth a try at Harbor Freight: > https://bit.ly/3oiG8Jn   I bought the HF visor today. Surprisingly it isn't bad at all, especially for the price, but I don't do hours of close work. And you do have to bend over close to the work, which the OP didn't want. For me though it means no longer having to find one of my kids when I need to read the fine print on a medication container, paint can, any of the usual things i struggle with.

Mike Coon <gravity@mjcoon.plus.com>: May 18 10:26AM +0100 In article <f1dda93b-3a89-4479-a27d-c2ea0130566fn@googlegroups.com>, timothy42b@aol.com says... > me though it means no longer having to find one of my kids when I need > to read the fine print on a medication container, paint can, any of > the usual things i struggle with.   What optics do you need to "find one of my kids"? ;-)

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