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Re: Low Cost Dummy Load
davemrtn
I am not saying it isn't, but I have never heard 'Resistor
Tolerance' related to standard deviations.
I am sure it's it used by the manufacturer to control their manufacturing process, but I think at lot of precision resistors (< 5% tolerance) manufactured these days use laser trimming to bring the parts to within rated tolerance. Maybe there is an engineer in our group that works for a resistor mfg that can give us the full skinny ?? On 5/11/2015 6:12 PM, 'John R. Lonigro'
jonigro@... [4sqrp] wrote:
-- David Martin - K5DCM Mountain Home, Ar. -+-+-+-+-+-+-+-+-+-+- "It's only "work" if you'd rather be doing something else" - Dean Kamen
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Re: Low Cost Dummy Load [1 Attachment]
dekle <dekle@...>
toggle quoted messageShow quoted text
Darryl:,
Let 'x' = the value of a resistor in parallel with a 51.2
Ohm resistor to yield 50 ohms equivalent resistance.
50 = 51.2 x / (51.2 + x) (Product over
the sum for 2 resistors in parallel.)
2560 + 50 x = 51.2
x (Multiply both sides by (51.2 +
x)).
2560 = 1.2
x
(Subtract 50 x from both sides.)
x = 2133.3
ohms
(Divide both sides by 1.2)
Power rating coming soon........
73
Bill
KV6Z
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Re: Low Cost Dummy Load
John Lonigro
I could be wrong, but I don't think a 1% resistor necessarily
means the value is within +/- 1%. I think there are some
statistics involved which might say, for example, that the
standard deviation is 1%, meaning there are about 40% of the
resistors in a particular lot that would fall outside the 1% value
and a few percent even falling outside the 2% value.
toggle quoted messageShow quoted text
And, of course, David is right that the error (or at least some of the error) could be coming from the measuring device itself. As they say, if you have one clock, you know what time it is. If you have multiple clocks, you have no idea... 72, John AA0VE
On 05/11/2015 02:20 PM, David Martin
davemrtn@... [4sqrp] wrote:
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Re: Low Cost Dummy Load [1 Attachment]
Don Wilhelm <w3fpr@...>
Darryl,
toggle quoted messageShow quoted text
I would definitely mount it on a larger heatsink. Do you have a heatsink from an old computer? That is one no-cost source of heatsinks. If you do not have one, you may want to ask at one of the computer repair places. Those Caddock Thick Film Resistors are good for dummy loads, but do not exceed their ratings - they can die a quick death. 73, Don W3FPR
On 5/11/2015 2:49 PM, kk5ib01@...
[4sqrp] wrote:
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Re: SSB?
Michael McEwen
If you can, try SSB on 7.285 tonight...7:30 and 8:30 CDT. This Monday night SSB net has been trying to get off the ground. I plan to try 8:30 for sure and maybe 7:30 if we are finished with supper. _ _ ... .. _ _ _ Doc K5OSA - QTH: EM04sr ARRL 4SQRP #801 - NAQCC #7625 - SKCC #10098 FISTS #17157 - OMISS #9886 LFSARC (Lawton/Fort Sill Amateur Radio Club) Michael T McEwen Lt Col, US Army, Ret Cellular Phone: 580 919-9205 Residence: 580 529-3412
On Mon, May 11, 2015 at 7:14 AM, Wayne Dillon wayne.dillon@... [4sqrp] <4sqrp@...> wrote:
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Re: Low Cost Dummy Load [1 Attachment]
Darryl J Kelly
Thanks for all the comments, meter is a old Fluke 79 Series II, good meter, can calibrate the lead resistance out, but the meter itself is not guaranteed calibrated. I was just pleased to get a decent dummy load that small, that accurate, and that cheap.
Darryl, KK5IB
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Re: Low Cost Dummy Load [1 Attachment]
Darryl,
That's only a half an Ohm tolerance, 50 x .01 = 0.5 plus/minus. Your meter may not be accurate enough to measure that. The value you measured might be the resistance of the test leads. You probably don't need to be concerned about that difference. Chuck Carpenter, W5USJ EM22cv, Rains Co. TX
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Re: Low Cost Dummy Load
davemrtn
Yes but, as you can see from his photo, he paid for a 1% resistor !!
For $11 (+ shipping), I would be calling the vendor. OR MAYBE, the error is in the device he is using to measure the resistance ?? On 5/11/2015 2:05 PM, Wayne Dillon
wayne.dillon@... [4sqrp] wrote:
-- David Martin - K5DCM Mountain Home, Ar. -+-+-+-+-+-+-+-+-+-+- "It's only "work" if you'd rather be doing something else" - Dean Kamen
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Re: Low Cost Dummy Load [1 Attachment]
Bill Cromwell
Hi Darryl,
toggle quoted messageShow quoted text
Don't even bother about a parallel resistor. Use it as-is. It's barely 2 percent off. How accurate is you DMM? How do you know? Our solid state radios will work happily into 75 ohm systems. That's a lot more *off* than 1.2 ohms - assuming your DMM is actually that close. 73, Bill KU8H
On 05/11/2015 02:49 PM, kk5ib01@gmail.com [4sqrp] wrote:
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Re: Low Cost Dummy Load [1 Attachment]
Wayne Dillon
Hi Darryl Should be 2K2, this equates to 50.0355 Ohms total effective resistance. Not sure on power as the 51.2 is only about 3% of the 2K2. Anyway why worry about the error? the error is less that 3% and that's better than most commercial dummy loads. Just my $0.02 worth. Be blessed Wayne - KC0PMH
On Mon, May 11, 2015 at 1:49 PM, kk5ib01@... [4sqrp] <4sqrp@...> wrote:
--
http://www.qsl.net/kc0pmh/ Under construction but please visit anyway.
QRP - EFFICIENCY AND SKILL, NOT POWER.
I'm British by birth but American by CHOICE! Jesus came to pay a debt He didn't owe because we owe a debt we cannot pay... The Lord bless you and keep you The Lord make His face shine upon you, and be gracious unto you The Lord lift up his contenance upon you and give you peace. God Bless from Wayne Dillon - KC0PMH Joshua 24:14-15 2 Cor 5:17 1 Jn 2:17 Membership Chairman - 4SQRP Group 4SQRP #95 FISTS 17184 FPQRP #342 (Flying Pigs QRP Club)
NAQCC # 0759 QRP-ARCI #11505 SKCC #1155T CW Ragchewers Anonymous #40
SOC #848 30MDG#1176 NEQRP #693 GORC #192 DMC (Digital Modes Club) # 06686
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Low Cost Dummy Load
Darryl J Kelly
This is my new low cost dummy load, made with a Caddock thick film non-inductive resistor. This one is 50 ohms at 1%, and rated at 100 watts, and costs about $11.00 from Mouser or Digikey. I realize the current heat sink will not be adequate for 100 watts, but it will suffice for the 5 and 50 watt calibrations of my K3, it does get warm to the touch. Only problem is resistance measures 51.2 ohms. What value of a parallel resistor would bring that down to 50 ohms? I calculate 1234.56 ohms or 1.2 K. Is that right? Also what would the power rating of the resistor need to be? Thanks.
Darryl, KK5IB
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NAQCC MWN
Scotty Long
Quick note the NAQCC Midwest MWN Net tonight 40m on or around 7117 kHz at 9pm CDT 0200 UTC...please listen up or down as the frequency may be busy at net time... If we have bad WX I'll unplug...crazy weather and QRN...Thank you for your understanding; have a great week...
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K8IQY "Magic Box"
Michael McEwen
Anyone have a functioning K8IQY "Magic Box" to sell? _ _ ... .. _ _ _ Doc K5OSA - QTH: EM04sr ARRL 4SQRP #801 - NAQCC #7625 - SKCC #10098 FISTS #17157 - OMISS #9886 LFSARC (Lawton/Fort Sill Amateur Radio Club) Michael T McEwen Lt Col, US Army, Ret Cellular Phone: 580 919-9205 Residence: 580 529-3412
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Send in your score
John Lonigro <johnlon@...>
I hope the lightning stayed away from your QTH last night, at least long enough to participate in the SSS. This is Dayton week and a lot of you will be busy packing the next couple of days. Before you forget, please send me your score, so I can keep the database up to date. Your submittal is simply your name, call, 4sqrp member number, and number of qualified QSOs. A "qualified" QSO is one made from 7:00-9:00 pm CDT, using 5 Watts or less, and exchanging call, state, and 4sqrp number/power. And soapbox comments are always appreciated. Please send them to secondsundaysprint@.... I hope to get the results out by Wednesday. In the meantime, I guess I'll start working on this year's certificates for the top operators. Hard to believe, but there are only 4 more SSS events remaining before I announce the winners. Where has the time gone? 72, John, AA0VE 4SQRP Contest Coordinator
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Re: SSB?
Wayne Dillon
I'll see if I can persuade my antenna on to 17m and then I'll report back (I'll listen out as well). have a blessed day Wayne - KC0PMH http://www.qsl.net/kc0pmh/ Under construction but please visit anyway.
QRP - EFFICIENCY AND SKILL, NOT POWER.
I'm British by birth but American by CHOICE! Jesus came to pay a debt He didn't owe because we owe a debt we cannot pay... The Lord bless you and keep you The Lord make His face shine upon you, and be gracious unto you The Lord lift up his contenance upon you and give you peace. God Bless from Wayne Dillon - KC0PMH Joshua 24:14-15 2 Cor 5:17 1 Jn 2:17 Membership Chairman - 4SQRP Group 4SQRP #95 FISTS 17184 FPQRP #342 (Flying Pigs QRP Club)
NAQCC # 0759 QRP-ARCI #11505 SKCC #1155T CW Ragchewers Anonymous #40
SOC #848 30MDG#1176 NEQRP #693 GORC #192 DMC (Digital Modes Club) # 06686
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Re: Head sets?
Don Wilhelm <w3fpr@...>
Doc,
toggle quoted messageShow quoted text
Another headset choice is the Yamaha CM500. I find it more comfortable than the Heil headset and has a very sensitive electret microphone. It can be found at Pro Audio sources such as Sweetwater Sound and B&H Photo The price is usually in the vicinity of $60 which is about 1/3 the cost of the Heil headset. It is not to be shipped outside the US and Canada for some reason unknown to me, but likely having to do with some trade agreements. The electret element does need a bias voltage, and it is not clear to me whether the LNR LD-5 is capable of providing bias on the mic AF line. If it does not, the CM500 has a little 'battery box' that can be used to provide that needed bias. This microphone is normally used at Pro-audio soundboards as monitor headphones and as a "talkback" mic, so it is not well advertized for ham use. Try one for SSB and I think you will be satisfied - the audio quality is very good as could be expected from the Pro-audio folks. My only objection is the extra long cord, I guess made for audio technicians pacing around their soundboard, but a few wraps of the cord secured with a twist tie takes care of the excess length. 73, Don W3FPR
On 5/10/2015 6:07 PM, Michael McEwen
mcewenk5osa@... [4sqrp] wrote:
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Re: Head sets?
Don Wilhelm <w3fpr@...>
Doc,
toggle quoted messageShow quoted text
I am having trouble understanding your situation. Pull the Heil Pro Set mic and headphone jacks out of whatever adapter they are now plugged into and you should see that they are 1/8 inch (or 3.5mm) plugs - unless someone has done surgery on your Heil Pro Set. The ProSet comes native with the 1/8 inch (3.5mm) plugs. If you are having concerns about the difference between "1/8 inch" and "3.5mm" plugs and jacks, have no fears, they are identical. More and more manufacturers and distributors are using the 3.5mm designation, but there are some that are 'glued' to the US "English measurement system" that they still refer to them as 1/8 inch. If you use your calipers, you can convince yourself that there is no difference between the two - if you find any, I believe you can resolve the slight differences by a quick perusal of the manufacturer's tolerances. 73, Don W3FPR
On 5/10/2015 6:07 PM, Michael McEwen
mcewenk5osa@... [4sqrp] wrote:
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Head sets?
Michael McEwen
I wish I could use my Heil Pro Set with my LNR LD-5, but the jacks are 1/8" and Heil does not make an adapter for that. What do you all recommend for a high quality headset that I could use? _ _ ... .. _ _ _ Doc K5OSA - QTH: EM04sr ARRL 4SQRP #801 - NAQCC #7625 - SKCC #10098 FISTS #17157 - OMISS #9886 LFSARC (Lawton/Fort Sill Amateur Radio Club) Michael T McEwen Lt Col, US Army, Ret Cellular Phone: 580 919-9205 Residence: 580 529-3412
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Re: CMOS chips at less than 3V supply?
Don Wilhelm <w3fpr@...>
You may find better luck with the 74HC family since it is rated to
work from 2 to 6 volts.
toggle quoted messageShow quoted text
One thing to keep in mind is noise immunity. As the supply voltage decreases, the margin between a valid logic level and the levels in the 'region of uncertainty' also grows smaller. The result is increased susceptibility to noise that gets onto the circuit wiring. Not the "noise" as we would hear in our receivers, but "noise" such as RF pickup, the pulses from one part of the logic circuit influencing others as the logic gates switch, as well as hum pickup from magnetic fields of AC transformers. I do not say that to be a bearer of doom and gloom, but to give you some hints about potential problem sources. Before concluding your design is sound when working at low voltages, subject the circuit to various sources of external stimuli to make certain it works under adverse conditions - remember, Murphy rules - it will fail when the use of a device is most critical, and when there are the maximum number of folks watching the demo. 73, Don W3FPR
On 5/10/2015 5:28 PM,
mbraner@... [4sqrp] wrote:
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Re: SSB?
Martin
17 works for me.
On May 10, 2015 4:05 PM, "Michael McEwen mcewenk5osa@... [4sqrp]" <4sqrp@...> wrote:
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