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Re: bALUN Common mode reject Z measurement
QUOTE: " Could you provide a bit more detail on your description:"
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QUOTE: 1. The actual antenna in the air. Following is a rough sketch of the antenna. The feed point is about 30-feet above soil surface. Below and to the west is a slope downward of roughly 35 to 40-degrees. Above and to the east is an upward slope of 23-degrees. The actual layout below should be rotated about the N/S axis by 180-degrees for the actual layout on the property. [image: image.png] The impedances noted are modeled in 4NEC2. QUOTE: "2. You say to this antenna is connected a ¡°450 set of wires¡±? Can¡¯t imagine what they would be, unless you were trying to say you feed the aerial with a 450 ohm feedline. Is this correct?" As above, the wires are a total length of 450-feet in the air. I feed it with parallel conductor transmission line. There is about 20-feet outside of 420-Ohm window line and 40-feet of parallel conductor line across the inside of the back of the garage. That consists of AWG #8 solid copper conductor spaced about 1-inch apart on electric fence standoffs. Then and finally roughly another 5-feet of the window line to feed the common mode choke. QUOTE: "3. If so, is your 450 ohm feed feedline actually measured at 450 ohms? Or is it JSC-1318 or something described as Zo = 450 ohms, but really 400 ohms? Yes, it was advertised as 450-Ohm window line. However, since I could, I actually measured it. It measured 311-ohms with a Vp of 0.882. This is an average of four readings made at 1.9, 4.0, 14.150, and 22.0 MHz. The advertised Vp is 0.91. I have not measured the impedance of the line across the back of the garage, but it should nominally be roughly 330-Ohms ( ) QUOTE: "4. A description of your CMC choke at the shack, connected on one side to the parallel feedline and out the other to coax? How many cores? Separate bifilar windings on one or two toroids? Or in series with two different materials #31 and a second with #43?" Do not ever.....EVER..... mix ferrite materials in a single assembly!!! Trouble will haunt you forever. ?? The CMC is connected between the shack end of the open wire feeder and the input of the single-ended L-network matching unit (home brew to take far more than the max amateur permitted power - which I do not have available). Therefore, both the input and output of the matching network are single ended, common mode. The output (50-Ohm end) of the matching network feeds roughly 2-feet of coax to the cross-needle SWR/PWR meter. From there, another 2-foot section of coax to the output of the AL-82 amplifier. The input of the amp passes through a switch to select either the Icom 7300 or the Icom 7610. I hope that is enough detail! A single 2.80-31 or 2.80-43 toroidal core is more than adequate to about 300 to 500 watts. I stack cores for more power handling capability. I have CMCs of both 2 and 3 stacked cores of both materialsy. All are bifilar wound with AWG #12 stranded copper wire insulated with Teflon (thickness enough to withstand 15 kV in non-field enhanced geometer). The bifilar windings encompass both cores. The cores are stacked on top of each other before winding. They range between 12 and 16 bifilar windings. I have one 4-inch 31 material wound with RG-400 coax which is just a current balun and, of course, not bifilar. Again, there is no "one-size-fits-all" as the suppliers have the amateurs believing. QUOTE: "Your observed results of Z CMC offered by each CMC choke ? In form Z=R +jX and related Reflection Coefficient Gamma Vector = rho Angle Gamma? Or dB." I prefer Z = R ¡À jX format. If you need, you can convert to value/angle. In doing matching networks and the like, the Z format is more useful. I'd just have to convert the value/angle to Z format to use it. I should note all the measurements are made with the HP 8753C with the associated HP 85047 S-Parameter Test set. Before making any measurements, that is calibrated in the conventional manner using HP cal standards. Nice explanation offers to inquiring ham looking for insights! Dave - W?LEV On Sat, Mar 11, 2023 at 2:39?AM AG6CX <edwmccann@...> wrote:
Regarding an excerpt from your post (perhaps missing a word or two?)-- *Dave - W?LEV* --
Dave - W?LEV |
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Re: nanovna saver manual
On Sat, Mar 11, 2023 at 08:37 AM, Neil Ackerley wrote:
If you want to take a screenshot of the graph in Saver right click it and then Save it. If you want a screenshot of the NanoVNA press the "Manage" button and select Screenshot. Roger |
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Re: Low power
Steve,
Yes you can do the calculations to find the through power to the antenna with the aid of a NanoVNA. Some things to consider. - Some transmitters will automatically slowly reduce their Tx power as the VSWR goes beyond a certain threshold. My Icom starts cutting back when the VSWR at the radio terminals goes above about 1.5 - Power will be lost in the transmission line to the antenna and this will increase with distance and VSWR. You can get a good estimate of the loss due to the transmission by several methods. Here are the ones I use. Calibrate you VNA and do an S21 measurement between CH0 (Port1) and CH1 (Port2). Find the loss at the frequency of interest using the marker and jog switch. If the coax feedline is already installed disconnect if from the antenna and measure the Return Loss at the frequency of interest. Record it as RLopen. Then short the far end and measure again. Record this as RL short. A good estimate is feedline attenuation is equal to (RLopen+RLshort)/4 for that frequency. The third method if you have a nanoVNA with a cable loss tool is to use that menu item. - You need to know the VSWR at the antenna in order to calculate the through power. You can measure VSWR directly at the antenna or use one of several other methods to calculate it. One method is to "de-embed the cable" by doing your SOL calibration at the end of the cable. This requires an assistant or a olt of running back and forth to do. Once you have de-embedded the cable the VSWR measurements made in the shack are very close to what is happening at the antenna feedpoint. The other method is to use one of the nomographs available from the ARRL and others that do the calculation based on attenuation of the cable. I have attached one for you reference. - When the VSWR at the antenna feedpoint is known the through power can be calculated or read from a table like the one attached. It gives what percentage of the power arriving at the feedpoint goes through and how much is reflected back. - Here is an example calculation for you. It does not account for connector loss and transmitter foldback and assumes that the transmitter tuner source impedance is 50 ohms. If 4 watts is transmitted on a cable that has 3 dB of attenuation at the frequency of operation only 2 watts arrives at the feedpoint. If the VSWR is a perfect 1:1 then 2 watts goes into the antenna. If the VSWR is 3:1 (Return Loss is 6 dB) then 75% or 1.5 watts of the arriving power goes into the antenna and 25% or 0.5 watts goes back down the cable to the transmitter. As it goes back down the cable it is attenuated by 3 dB so .25 watts is absorbed by the transmitter or tuner source impedance. The total power dissipated in the transmission line as heat is 2 +.25 - 2.25 watts. Roger |
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Re: Through calibration
#calibration
Using short coaxial cables with alligator clips on the end for S11 and S21 can easily lead to erroneous results. At best it is only useful for measurements in the HF range. There are several reasons for this...
- In order to get decent results you need to establish a good reference plane. In order to get a good reference plane the distance used between the measurement points must be the same for the SOL calibration. The measurement of the DUT must also be made at the reference plane. Using alligator clips that are at the end of leads connected to a coaxial cable requires at a minimum that everything be held in place for SOL and measurements. A different distance between the clips for the short, open and load and DUT measurement will result in errors in the measurement. How much error depends on what kind of measurement is being performed. - Users have to be careful what they use for the 50 ohm calibration load. Leaded components have inductance in the wire leads and in the body of the resistor if carbon or metal film resistors are used. Never use a 50 ohm dummy load because they have considerable inductance. - The wires coming out of the 50 ohm coaxial cable to the alligator clips form a higher impedance transmission line that increases the further the leads are separated. At VHF and above they act like a dipole antenna and you get common mode current on the outer surface of the shield. Try to "calibrate out" this arrangement can lead to errors. - For S21 measurements stray capacitance and inductance will affect the measurement (especially the S21 phase). To see what I mean try connecting a 100 ohm resistor between the two clips and see of you get 6 dB loss with minimal phase shift. Measuring components like resistors, inductors, ferrites, capacitors and baluns requires a test jig that is up to the task if you want results you can believe. If you want to find resonant frequencies of components like traps, inductors or capacitors you need a proper test setup. There have been many posts by knowledgeable users in this group on how to construct low cost test jigs that give accurate results up to 900 MHz. or so. This group contains a treasure trove of information on this subject in the wiki and the message archive. Roger |
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Invitation to present to the McKinney Amateur Radio Club
Hello Nanovna user group. I have subscribed to this group and have followed many great issues onto resolution.
Allow me to introduce myself, my name is Larry Land (Ki5oez), VP of the McKinney, Texas, Amateur Radio club. One of my duties in the club is to find presenters to present in person or virtually via Zoom to our club members. I thought I would reach out to your group to see if a member would be interested in doing an in person/virtual presentation to our club on using the NanoVna regarding ham radio. If instead you have a canned presentation that would be welcomed as well. Our club meets on the 2nd Tuesday of each month at 7PM Central time with the presentation to start between 7:15-7:30 and duration should be under 45 minutes, but we are flexible. We would also be happy to pay for your dinner prior to the meeting if presenting in person. The following dates are available: September 12, and November 14, 2023. (and possibly May 9, but I am holding out for a ¡°contesting¡± elmer in time for Field day) Thank you for your time and consideration in this request. Larry Land, ki5oez Vice President McKinney Amateur Radio Club Cell: (817)-312-4618 10292 Burnt Mill Lane Frisco, Texas 75035 vicepresident@... PS. We wish to challenge our members to learn and grow in our radio hobby. This is my first year as VP, and I feel I have been neglecting the more experienced members and need to challenge the less experienced members to grow. I earned my element 4 in late 2021, and the Smith Chart came as a surprise, but it did help demonstrate and iron out impedance issues. It would be great if we could introduce and challenge the general class members and, at the same time, refresh the extra members knowledge base. I believe the NanoVna is a great tool that can help solve many of the Ham¡¯s problems. Thanks again for your consideration. Sincere 73, Larry Ki5oez |
Roger Need
Larry