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Re: Impedance matching for the audio stage
A common 50 Ohm input impedance amplifier design evaluation:
Wayne has used this design for RF amps in K3, KX3, KX2, and K2. And K2 post mixer amplifier. There are other examples out in the WWW. Some combine AC feedback with DC biasing. For this example, feedback is AC coupled for adjustment isolation. An observation, many of the examples suggest 50 Ohm in/out gain of about 15dB. Several different bias selections on my bench resulted with about 15dB gain. John KN5L |
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Re: #Wanted
#wanted
it is 100 x 100 mm
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lz7dp, dim On Wednesday, May 22, 2019, 12:08:35 PM GMT+3, MVS Sarma <mvssarma@...> wrote:
NORCAL is it within 10 x 100mm? On Wed, May 22, 2019 at 12:01 PM Dimitar Pavlov via Groups.Io <lz1dpn= [email protected]> wrote:
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Re: #Wanted
#wanted
MVS Sarma
NORCAL is it within 10 x 100mm?
On Wed, May 22, 2019 at 12:01 PM Dimitar Pavlov via Groups.Io <lz1dpn= [email protected]> wrote:
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Re: #Wanted
#wanted
Will be cheaper to order 5 pcs with gerber files (in groups.io)? from China (with DHL shipping, for 5$ all).
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lz7dp, Dim On Sunday, May 19, 2019, 4:31:45 AM GMT+3, <graememorgan72@...> wrote:
Hi All, Would anyone in VK have a Norcal 40A PCB they are willing to sell? 73, Graeme VK5GG |
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Re: KC-1 Problems & Reset?
k6whp
Belay this request. It was a cockpit error. Somehow I tinked with the Wn (weighting) command and it through off the whole magillah. Now don;t I feel the fool?
Things are back to normal now. -- William, K6WHP "Cheer up, things could get worse..so I cheered up and, sure enough, things got worse!" |
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KC-1 Problems & Reset?
k6whp
My NorCal 40A (Wilderness Radio version) has become sick and I am wondering if there's a way to do a reset/reboot. The code speed is stuck at 25 WPM irrespective of the speed pot setting -- full CCW or CW. Any ideas?
Thanks in advance. -- William, K6WHP "Cheer up, things could get worse..so I cheered up and, sure enough, things got worse!" |
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Re: KN5L EFHW Unun
Also, open short method is for a conventional two winding transformer.
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Unun demonstrated is an auto-transformer. It is impossible to fabricate a matching two winding transformer with same k value as an auto transformer. A matching two winding transformer will always have k value slightly lower than an auto transformer. This is because an auto transformer has a k value of one for the common winding. Replacing common wire with two wires, to form a conventional transformer will pick up k < 1 for the two wire replacement. John KN5L On 5/21/19 8:33 AM, John KN5L wrote:
Hi Steve, |
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Re: KN5L EFHW Unun
Hi Steve,
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I've tried measuring k near one using inductance measurements with limited success. Confirming SimSmith matches inductance measurements is a good question. documents the process using a transformer with measurable k value. Process compares SimSmith matching method, open short method, and Series-adding Series-opposing method. After years of using SimSmith, I'm rather confident with the transformer model. John KN5L On 5/21/19 8:16 AM, Steven Dick wrote:
Wow that k value is excellent. Can you confirm with open/short test just to |
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Re: KN5L EFHW Unun
Wow that k value is excellent. Can you confirm with open/short test just to
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verify that actual measurement is in agreement with the Sim Smith model? Thanks -----Original Message-----
From: John KN5L Sent: Tuesday, May 21, 2019 8:38 AM To: [email protected] Subject: Re: [qrp-tech] KN5L EFHW Unun Hi Steve, This Unun design uses winding to winding capacitance for leakage inductance compensation. Capacitance to leakage inductance ratio tuned by moving primary windings within secondary windings, as shown in the Unun photo. k increases as primary windings are physically closer to secondary windings. I have found it's almost impossible to use classic inductance measurements for k measurements approaching one. My preferred method is matching a SimSmith transformer model to measurements, as shown in the web page under the two titles starting with "2 X FT114-43 4T:30T 3300¦¸ Load SimSmith." SimSmith model k for this Unun is .996. John KN5L On 5/21/19 7:11 AM, Steven Dick wrote: Hi John. That UNUN appears to have very good performance without the need |
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Re: KN5L EFHW Unun
Hi Steve,
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This Unun design uses winding to winding capacitance for leakage inductance compensation. Capacitance to leakage inductance ratio tuned by moving primary windings within secondary windings, as shown in the Unun photo. k increases as primary windings are physically closer to secondary windings. I have found it's almost impossible to use classic inductance measurements for k measurements approaching one. My preferred method is matching a SimSmith transformer model to measurements, as shown in the web page under the two titles starting with "2 X FT114-43 4T:30T 3300¦¸ Load SimSmith." SimSmith model k for this Unun is .996. John KN5L On 5/21/19 7:11 AM, Steven Dick wrote:
Hi John. That UNUN appears to have very good performance without the need |
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Re: KN5L EFHW Unun
Hi John. That UNUN appears to have very good performance without the need for a capacitor across the primary as used in many commercial units. That implies to me that it has relatively low leakage inductances. It would be interesting to measure relative coupling from primary to secondary by measuring primary inductance of the UNUN with secondary open and then measure primary inductance again with the secondary shorted. From that, a lot of data can be derived.
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Thanks, Steve K1RF -----Original Message-----
From: John KN5L Sent: Tuesday, May 21, 2019 7:08 AM To: [email protected] Subject: Re: [qrp-tech] KN5L EFHW Unun Hi Allison On 5/20/19 8:24 PM, ajparent1/kb1gmx wrote: Also did you actually test the unun with a real antenna? Look under the title: "Antenna Measurement." John KN5L |
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Re: Impedance matching for the audio stage
One simple method you could use if maximum power transfer isn't a must
would be to shunt the output of the mixer with 50 ohms to ground. You could always make up audio gain. 73- Nick, WA5BDU On Mon, May 20, 2019 at 2:41 PM Richard Seguin <richard.seguin@...> wrote: Hello, |
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Re: KN5L EFHW Unun
ajparent1/kb1gmx
Eznec rarely get the ground effects right. You need Nec4.2 engine to model that correctly.
too many years of modeling in the office and then going out on the grass and finding out they dont match other than generally. If you didn't measure the ground for the frequency your using an educated guess. I've found that create errors and also the myth of the magic combination when its specific to a installation. Also it tends to vary with season (wet/dry). Also did you actually test the unun with a real antenna? As to the unun doing what you intend that's not in question. It looks good. What is the questiondoes the wire really behave at 2450 or 2800 ohms (nec model) which is less than 14% difference. What if the wire is really 3300 ohms obviously the 1:56 will be better but not perfect. Yet 3300/2450 is only a swr of 1.34:1 and an acceptable match. I also said even if your wrong, to get to 2:1 you need to be wrong by a factor of 2 and that's a huge miss. What I didn't add is if you tweak the wire length you can get to an acceptable SWR in some cases (usually with a higher complex impedance and more RF on the shield). The trick for endfeds is a transformer that is in the middle of the likely range or best exact which is not easily done. For testing I use a bridge, and other instruments or an adjustable L network (the later can match the wire. Then I put a variable resistor from the load port and ground and adjust the resistor for SWR of 1:1 and that was the feed point resistance of the wire. Why do both? often I have to lower one end to measure and the other I can use a adjust and elevate (step and repeat) to see the difference and often height is a factor. Its more for those that don't understand that an end fed wire like a dipole has the same variation in feed point impedance with height above a real ground. I've included a white paper on how to make a resistive SWR bridge. fairly stock design for 50 ohms but if you want to measure a real antnena you may want the bridge to be adjustable to find out the antennas actual impedance. the design is a GQRP design and R1 determines the "characteristic" impedance. Making R1 variable (about 5k for EFHW) and using a RF source you can both find the resonant frequency and the actual resistive portion of the antenna at its feed point. Note R5 should be in series with a larger choke to get a RF resistance of about 15k ohms. [its to get the metwe out of the RF circuit.] Failure to do that will have 1K across the antenna terminals by default and create errors. Power to test in in the less than a 100 mW range and depending on meter sensitivity 10mW may be enough. First set the R for about 2 to 3K then adjust the RF source for null response (very low indication) then adjust the resistor to minimize the null while adjusting the RF for the best null. The result will be the resistor is the load resistance and the null frequency is the actual resonance of the wire. The pot needs to be non inductive. Usually standing on a ladder doing that, less then fun if you like me and height adverse. Reason is to get the antenna up and also a short length of coax. a decade of antenna design work and testing left me with a large bag of tricks to get the data and confirm the result. The common Tayloe design using a led may work were the R1 resistor is adjustable but the led only lights with a lot of RF and is insensitive for this use. A meter could be added for better null sensitivity. When measuring high impedance or low I use the HP4191A and a bridge like the one described to get answers as accurate as the HP (to about 4 digits.). I also have a 50mw DDS RF source as the way to drive measurements. A SA like the Rigol 815T or any with tracking generator can be used to make that measurement using a resistive bridge. Experience says better than 8357A PNA without a calibrated matching transformer and math to get the real impedance (most PNAs do poorly at high resistive loads without fixtures). Allison |
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Re: KN5L EFHW Unun
Hi Allison,
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I'm somewhat confused by your response. A Unun ratio was selected for a specific test antenna. An EZNEC model, which matches test antenna dimensions, is also included. Is there an issue with test antenna measurement or EZNEC model somewhere? Two Unun ratios are presented, demonstrated 56:1 and 49:1 for antennas with lower impedance. John KN5L On 5/20/19 4:05 PM, ajparent1/kb1gmx wrote:
John, |
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Re: Impedance matching for the audio stage
Paul Martin
Rick Campbell KK7B designed a series of direct conversion radios with 50 ohm audio amps. See this link for details. May be some ideas you can use in yours. They work very well.
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Paul On May 20, 2019, at 3:48 PM, k7da <k7da@...> wrote: |
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Re: KN5L EFHW Unun
ajparent1/kb1gmx
John,
For matching a EFHW its important to know that while there are all manner of magic ratios the actual feed point resistance is the only real one. That varies with height and orientation. The other piece of magic is if you stick a stake in the sand can call it 2000 or 3000 ohms the 2:1 SWR circles are: 2000 nominal is 1000 to 4000 ohms 3000 nominal is 1500 to 6000 ohms So even if we are wrong the range for OK is still rather wide. I tend to use lower values for antennas like 80 and 160M as they tend to be close to the ground, and higher for 20M antennas. Its rare that I see a SWR greater than 1.3:1 which suggests its likely around there somewhere and more than adequately close. For longer multiband antennas the resonance is likely lower as you go up due to total wire length having a lower impedance. Why? All antennas that are horizontal exhibit impedance where ever they are fed, even in the middle, that varies with height. I've included a often seen graph that can be worked for any frequency and height. An added note is that height affect total length for low antennas more than high or verticals so a half wave can be something other than a numerical half wave due to height. FYI measuring a real antenna is a bit tricky as 50 ohm gear gives wild results at 3Kohms. A simple bridge with one leg of 5000 ohms (variable pot) and the antenna as the other can be easily used to measure the actual under resonance. The RF source can be a few milliwatts of RF and the detector for the bridge is a diode detector and a simple 50ua meter as the goal is a null. Then measure the port and you have the real part in ohms to typically for most digital multimeter better than 3 places (maybe more but three is more than enough). Allison |
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Re: Impedance matching for the audio stage
Richard Seguin
This is very helpful, thank you
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On Mon, May 20, 2019 at 5:32 PM Pat Byers <ve3eur@...> wrote:
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Re: Impedance matching for the audio stage
ajparent1/kb1gmx
THe most common is one of two... Transformer from 50 ohms to say 500-100 ohms to
match the base of a transistor. The problem with that is bandwidth as its a poor match across the DC to many mghz of the DBM output. Another is hum pickup from magnetic fields. The more common used in radio circuits is a common base amp with an emitter current of .5ma which is about right for 50 ohms. This is the path that KK7B took and it offers both good voltage gain and a good match to the dbm. That is detailed in the book EMRFD, Experimental Design for RF Design, ARRL press. Worth its weight and more. Allison |
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Re: Impedance matching for the audio stage
It's fairly important that the DBM see 50 Ohms. The master for matching these product detectors to the audio chain is Rick Campbell KK7B who designed the R1, R2, miniR2 and microR2 receivers among others. Here's a link to the R1 <>. Just seach on kk7b for the others.
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Hope this helps. 73, Pat? ? VE3EUR On Monday, May 20, 2019, 3:41:52 p.m. EDT, Richard Seguin <richard.seguin@...> wrote:
Hello, I'm designing an audio stage after a BFO diode ring mixer and I seem to be having trouble converting a 50-ohm impedance to something the amplifier can handle (10K input).? I know how to convert impedances with RF signals using toroids, and I assume that the exact same would apply to audio.? Does anyone know of a toroid or ferrite core that is decent at audio frequencies? Richard (VE1XOR) |
Nick Kennedy
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