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Post your Shack, Shop, Repair room / Just getting off of the ground
« on: September 18, 2019, 05:36:32 PM »
Been collecting gear for several years. Just now getting around to setting it up.
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Test Equipment / Re: RF sampler / demodulator for oscilloscope
« on: September 18, 2019, 05:10:08 PM »
Just to be sure, check the video. That 690 K, should be 690 ohm.
It is not a danger to equipment... it affects the accuracy.
With 47K nominal over 690 ohm in parallel with the load of 50 ohms (the cap is negligible at almost any RF) you get a voltage divider of 46.6/47046.6 which is almost exactly 1/1000 (.00099051 in fact) which is almost spot on -60 dB attenuation (60.08).
If you do it with 690K that 46.6 goes up to 49.99 which makes your voltage divider 49.99/47049.99 which works out to -59.47 dBm.
It isn't a huge difference but some users may value that.
According to my calculations, at 1000 Watts RF In the 47K would dissipate 1.06 watts. So use a 2 or 3 watt piece for safety.
At 1500 watts I show 1.59 watts so , again, a 3 watt piece, maybe 5 watts and that should handle it.
For other fun, 15K instead of a 47K would be -50 dB attenuation (15K will dissipate .33W at 100W RF/ 2w at 600w RF/3.3w at 1000W RF)
4.7K would be -40 dB (4.7K will dissipate .107w at 10w RF / 1.04w at 100w RF).
It is not a danger to equipment... it affects the accuracy.
With 47K nominal over 690 ohm in parallel with the load of 50 ohms (the cap is negligible at almost any RF) you get a voltage divider of 46.6/47046.6 which is almost exactly 1/1000 (.00099051 in fact) which is almost spot on -60 dB attenuation (60.08).
If you do it with 690K that 46.6 goes up to 49.99 which makes your voltage divider 49.99/47049.99 which works out to -59.47 dBm.
It isn't a huge difference but some users may value that.
According to my calculations, at 1000 Watts RF In the 47K would dissipate 1.06 watts. So use a 2 or 3 watt piece for safety.
At 1500 watts I show 1.59 watts so , again, a 3 watt piece, maybe 5 watts and that should handle it.
For other fun, 15K instead of a 47K would be -50 dB attenuation (15K will dissipate .33W at 100W RF/ 2w at 600w RF/3.3w at 1000W RF)
4.7K would be -40 dB (4.7K will dissipate .107w at 10w RF / 1.04w at 100w RF).
3
Test Equipment / Care and Safety for Spectrum Analyzers
« on: July 15, 2019, 10:16:51 PM »
Somewhat depressed. 
I picked up an older Hameg Spectrum Analyzer at a hamfest back in May. I know very very little about them but I am learning fast. Catching up on dBs, dBms, attenuation.....but the big thing I am concerned about is the safe handling of what I stuff in to it. I know that you have to attenuate the transceiver down to a safe level but it seems that there are a number of ways to do this... and all of them appear to be in the thousands of dollars. Not only that, I have not found any place that discusses just HOW you set them up.
Some say "use attenuators". A nice 100W 40db would knock most low powered transceivers down (thinking 5 - 10 watt, I still love CBs!!!!!) BUT here is the question.... if you go from the radio to the attenuator and the attenuator to the SA...... does the attenuator serve as a dummy load for the radio? It says it is 50 ohms input and can handle 100 watts.... so I would think so...BUT I can't find a place that discusses it.
Others use samplers. I have seen some that tap off of the RF on the way to or IN a 50 ohm dummy load. They just tap resistors off...more or less a voltage divider... and take that point out to the sample port and feed it to the SA. Is this calibrated enough to allow measurements? And....the dummy load is dissipating all of the power...and the resistors seem to be high enough that they don't pull a lot of current....so they don't have to be very high powered themselves. Again, I have found no place to discuss it.
Other people I see use directional couplers. They seem to be a pass through for the main RF line that you might connect up to a dummy load AND they have a sample port that is some number of dB down. If the dummy load is dissipating all of the power..... how much power handling does the directional coupler have to account for? It doesn't seem to me like it would be much..... the dummy load is doing the real work.....but, again, I have found no place to discuss it.
From what I have splattered here.... does anyone know of a resource that offers this kind of info.... I really want to learn what options are for connecting these things up so I don't destroy it on the first go round.
Any ideas?
I would most certainly appreciate it.
I picked up an older Hameg Spectrum Analyzer at a hamfest back in May. I know very very little about them but I am learning fast. Catching up on dBs, dBms, attenuation.....but the big thing I am concerned about is the safe handling of what I stuff in to it. I know that you have to attenuate the transceiver down to a safe level but it seems that there are a number of ways to do this... and all of them appear to be in the thousands of dollars. Not only that, I have not found any place that discusses just HOW you set them up.
Some say "use attenuators". A nice 100W 40db would knock most low powered transceivers down (thinking 5 - 10 watt, I still love CBs!!!!!) BUT here is the question.... if you go from the radio to the attenuator and the attenuator to the SA...... does the attenuator serve as a dummy load for the radio? It says it is 50 ohms input and can handle 100 watts.... so I would think so...BUT I can't find a place that discusses it.
Others use samplers. I have seen some that tap off of the RF on the way to or IN a 50 ohm dummy load. They just tap resistors off...more or less a voltage divider... and take that point out to the sample port and feed it to the SA. Is this calibrated enough to allow measurements? And....the dummy load is dissipating all of the power...and the resistors seem to be high enough that they don't pull a lot of current....so they don't have to be very high powered themselves. Again, I have found no place to discuss it.
Other people I see use directional couplers. They seem to be a pass through for the main RF line that you might connect up to a dummy load AND they have a sample port that is some number of dB down. If the dummy load is dissipating all of the power..... how much power handling does the directional coupler have to account for? It doesn't seem to me like it would be much..... the dummy load is doing the real work.....but, again, I have found no place to discuss it.
From what I have splattered here.... does anyone know of a resource that offers this kind of info.... I really want to learn what options are for connecting these things up so I don't destroy it on the first go round.
Any ideas?
I would most certainly appreciate it.
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Test Equipment / Using PLJ-8LED-H frequency counter?
« on: February 13, 2019, 11:01:00 AM »
Has anyone eve bought one of those inexpensive frequency counters on Ebay, the PLJ-8LED-H and actually used it as a bench frequency counter?
(here is a link)
https://www.ebay.com/itm/PLJ-8LED-H-RF-Signal-Frequency-Counter-Meter-Tester-Module-0-1-1000MHz-LED-HZ/283288431654?hash=item41f54e6c26:g:~zoAAOSwQH5cBV2N:rk:8:pf:0
By specs it should handle it but what I DON'T know is, does it need any kind of buffering/level changing on the front end to be sensitive enough to do things like check reference oscillator or VCO frequencies when diagnosing problems?
I would be interested to hear of anyone doing so.
I have one, and I ALSO have the perfect opportunity to use it... I just haven't done so yet. In advance I was wondering what others may have found out about its suitability for this purpose.
I have a Cobra 21LTD that was my father-in-laws back in the day. It was given to me when he passed away. I re-capped it....but was WAY WAY too dumb to check it first and see if it worked at all... so I don't know if it did or not.
After the re-cap, the light comes on, but no RX or TX. I put a scope on the PLL and was at least able to determine that it is NOT IN LOCK. I see a MIGHTY LOW signal on the reference that appears to be about 10.24 MHz and the VCO looks like it is doing something.... I'd just like to know what their frequencies are.... so that is why I am asking about this. Looking up all the info I can get on the TC9106BP PLL and actually have quite a bit.... just time to sit down and do it!
Thanks in advance
(here is a link)
https://www.ebay.com/itm/PLJ-8LED-H-RF-Signal-Frequency-Counter-Meter-Tester-Module-0-1-1000MHz-LED-HZ/283288431654?hash=item41f54e6c26:g:~zoAAOSwQH5cBV2N:rk:8:pf:0
By specs it should handle it but what I DON'T know is, does it need any kind of buffering/level changing on the front end to be sensitive enough to do things like check reference oscillator or VCO frequencies when diagnosing problems?
I would be interested to hear of anyone doing so.
I have one, and I ALSO have the perfect opportunity to use it... I just haven't done so yet. In advance I was wondering what others may have found out about its suitability for this purpose.
I have a Cobra 21LTD that was my father-in-laws back in the day. It was given to me when he passed away. I re-capped it....but was WAY WAY too dumb to check it first and see if it worked at all... so I don't know if it did or not.
After the re-cap, the light comes on, but no RX or TX. I put a scope on the PLL and was at least able to determine that it is NOT IN LOCK. I see a MIGHTY LOW signal on the reference that appears to be about 10.24 MHz and the VCO looks like it is doing something.... I'd just like to know what their frequencies are.... so that is why I am asking about this. Looking up all the info I can get on the TC9106BP PLL and actually have quite a bit.... just time to sit down and do it!
Thanks in advance
5
New member welcome / New member from Houston area
« on: December 13, 2016, 01:10:49 PM »
Hello one and all. My name is Bob from the Houston, TX area.
From January 1975 to February 1977 I attended DeVry Institute of Technology in Dallas, Texas then worked 11 years on the Space Shuttle Flight Simulator at NASA JSC in Houston. About 9 years into that job I made the jump to the "dark side" of software development working first in operating system internals, then left and joined Concurrent Computer Corporation as a field analyst for 18 years. I now work at Baylor College of Medicine in Houston as a software developer.
At this point in my life, I find that I am missing something..... electronics. Most of my work at NASA was in digital systems: Computers, signal conversion equipment, various hardware interfaces and such.
What I am longing to get back to... is communications and particularly tube guitar amps. Back in the day, I fixed a CB or two for other people.... I still have a few that I would like to go through and renovate to make them usable again. Guitar amps... I'd love to fix them, design them... just "have a ball".
So while I have a decent background.... I am misging a lot of practical experience and that is what I am seeking to remedy now!!!
From January 1975 to February 1977 I attended DeVry Institute of Technology in Dallas, Texas then worked 11 years on the Space Shuttle Flight Simulator at NASA JSC in Houston. About 9 years into that job I made the jump to the "dark side" of software development working first in operating system internals, then left and joined Concurrent Computer Corporation as a field analyst for 18 years. I now work at Baylor College of Medicine in Houston as a software developer.
At this point in my life, I find that I am missing something..... electronics. Most of my work at NASA was in digital systems: Computers, signal conversion equipment, various hardware interfaces and such.
What I am longing to get back to... is communications and particularly tube guitar amps. Back in the day, I fixed a CB or two for other people.... I still have a few that I would like to go through and renovate to make them usable again. Guitar amps... I'd love to fix them, design them... just "have a ball".
So while I have a decent background.... I am misging a lot of practical experience and that is what I am seeking to remedy now!!!
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