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On Tue, Sep 5, 2023 at 10:24 AM, Mark KQ4EKK wrote:

Is there a way to select those 5 options in NanoVNA-APP?
|S21|
S21 |Z| shunt
S21 |Z| series
S21 R+jX shunt
S21 R+jX series

NanoVNA app does not calculate/plot S21 impedance measurements. BTW S21 impedance measurements are not very accurate using NanoVNA's because they do not do 12 point error calibration and do not have precise 50 ohm source and termination impedances. You also need a good test jig or stray capacitance will greatly affect the measurements. If you search the archives of this group you will find many discussion posts on this topic. Using a -H4 I have found that i can make fairly good measurements from 2 to 3000 ohms impedance using the s11 shunt method.

Roger

ae1th@, you mention this is the case with gift cards... I can see that as being a policy. Gift cards, while being great options, they have no real tracking ability especially on the internet. Many scammers out there are stealing money from people with fake IRS or whatever scams and are asking for payment in the form of gift cards. Some unsuspecting people and many of them being people that usually cant afford to lose money, fall for this scams and pay. And then there are the straight credit card frauds or theaves that go to stores and buy gift cards to convert it quickly and then use the gift card or sell the gift cards. Paypal caught onto this and probably made it a policy to not use gift cards. People can also quickly convert the gift cards to bitcoin via paypal payments and then they are clean and completely anonymous when purchasing. So, no more paypal as a gateway.... Price we need to pay for those that are bad out there.

How are folks doing on a 40m NVIS antenna for daytime short-range COMS?

A bit more tweaking of my 40m closed LOOP NVIS antenna for 7075 kHz
Less than 1.5:1 SWR across 40m band
Over 50dB return loss at resonant frequency 7075 kHz

The Nano VNA graphs make this loop antenna easy to "tune up"
I'm ready to try it out: 7068 kHz Sunday at 10 AM EDT with THOR 22


This antenna is about 2-3 S-units (15dB) stronger than back-to-back 40m 7 ft Hamsticks
and also a few S-units stronger than my 40m vertical (34 ft lashed to a tree) on daytime coms

de k3eui

the problen with visa-ebay-paypal is with ebay-paypal, i can not use any of my birthday visa gift cards on ebay or paypal, visa said - go to a store with an id and use, i have used on the net for cvs-walmare - walgreens with no trouble, it is a problem between ebay and paypal which they wont devulge. fyi

Hello All,
I have attached a pic of the NanoVNA Saver Display Charts options.
Is there a way to select those 5 options in NanoVNA-APP?
|S21|
S21 |Z| shunt
S21 |Z| series
S21 R+jX shunt
S21 R+jX series

NanoVNA Saver 0.6.2 shown
NanoVNA-App v1.1.215 using

Thanks in advance,
Mark

No, none of my computers and other devices has been compromised.
I will make no further comments on this pointless exchange because it has veered way off topic for the reflector plus you are dead set on exonerating PayPal and any other "reputable" payment processors of any responsibility.
73,Julio VE3FH

A trans publication on
/g/eznec/message/397
--
Fran?ois

On Mon, Sep 4, 2023 at 03:00 PM, Manfred Mornhinweg wrote:

There are basically two ways to use traps in antennas.

A third way that avoids rules of thumb uses an iterative procedure with automatic optimizers to adjust everything for maximum performance:



Brian

A trap is simply a resonant circuit. You can measure it like any resonant circuit. But since traps are build to handle significant power, they are usually somewhat large, which makes them more sensitive to their surroundings. So a trap connected to the NanoVNA will probably measure a little different than its actual behavior when installed in the antenna.

The important curve of a trap is that of its reactance over the frequency range of interest. Traps are usually parallel resonant circuits, so the reactance will start low and inductive at low frequency, increase with frequency, reach a very high value at its resonant frequency, wrap over to a very large value of capacitive reactance, and this capacitive reactance will diminish with further increasing frequency. The important things are what's the resonant frequency, and how steeply the reactances vary with frequency.

There are basically two ways to use traps in antennas. The simpler one is to make the trap resonant in the middle of the higher band, then install it in a position so that the inside leg of the antenna resonates on that band too. The trap acts like an insulator on this band. On the lower band the trap has an inductive reactance, and depending how high it is (which depends on the L/C ratio of the trap), the outer leg needs to have a specific length to make the antenna resonate on that lower band. The total length of the antenna is always shorter than a trapless antenna for the lower band.

This method is easy to understand and tune, but the resonance on the higher band is pretty narrow, and the trap has to stand up against a very high voltage on that band. So another method can be used, that places lower stress on the trap and also results in a better bandwidth: The trap is made to resonate in between the two bands. On the lower band it will still be inductive, so the total antenna length is still shorter than a trapless antenna for that band, but on the higher band this trap is capacitive, electrically shortening the antenna. So the entire antenna works on both bands, the antenna is of a length between that of of trapless antennas for the lower and the higher band, the trap sits in a location where the voltage is moderate on both bands, so it's less lossy and can be smaller, and the trap works on its reactance slopes on both bands, rather than working on the resonance peak on the higher band. This makes the antenna more broadband than in the other case, on the higher band.

So the second method is clearly the better one, but it's a little harder to calculate and tune properly, because the trap's resonant frequency, its L/C ratio, the total antenna length, and the position of the trap, all interact and all have an effect.

One way to do is is to decide the antenna length first. For example for center frequencies of 3.7 and 7.1MHz, 15 meters would be a good length for a quarter wave element with this kind of trap. Then decide the trap position. I would try to put the trap in the middle of the element, or even closer to the feedpoint. Then calculate or measure what inductance you need there to resonate the antenna on 3.7MHz, and what capacitance you need for a 7.1MHz resonance. Then calculate the inductance and capacitance you need in a resonant circuit to get them. The ratio between them will also determine the resonant frequency of the trap. Build the trap, measure it with the NanoVNA , adjust it, then install it in the antenna and either pray or swear, depending on your preference. Then start the usual game of tweaking the antenna until it works fine on both bands.

To do the actual measurent, you don't need to bother with both ports. It's enough to connect the trap to the main port. I suggest that you connect cable pigtails to the NanoVNA, long enough to comfortably reach the ends of the trap, while the trap isn't too close to the NanoVNA. Calibrate the NanoVNA with these pigtails, arranging them roughly in a loop for the short and load tests, and roughly in the positions they will be when connected to the trap, for the open calibration. Then connect the trap and measure the reactance over the desired frequency range, as far away as possible from other stuff, specially conductive one.

I think this is a good demo:



Ralph’s channel is very informative.

Alex

Hello

I do it with my NanoVNA but connected to the PC on nanovan-saver. I have a 1 m coxial extension cable (RG223 U) and I calibrate at the end of this cable. I place a small 3 turns coil on a ? 12 mm at the end of the coaxial. I couple this coil as little as possible with the trap and that gives the PJ 19.188 MHz

Then as an attachment
- S11 with the trap in parallel on port 0
- S21 with the trap between port 1 and port 0

The trap is made with 5.5 turns and here is what it corresponds to in Coaxial Trap Desing
The difference between the two types of connections shows a deviation at the resonance of 783 kHz. Each time the trap is placed on a block of expanded polystyrene.


Which frequency to choose? ? ? ?
:(

73
--
F1AMM
Fran?ois

I wrap a few turns around the trap. Scan the RL abd look for a dip like I used to with a GDO in the old days. I still use my GSO which I fund easier as I get an audio tone which dips as I tune across the resonance. The frequency is easily picked up with a receiver or frequency counter.

hi,

SV4401A is a product of SYSJOINT, please visit for more details

hi,

Is the coaxial trap a two-port device? If so, connect the VNA ports to the trap ports and observe the logmag trace, just like testing a filter.

I feed the RFfrom a signal generator through a resistor, then read the
voltage across the trap as it is tuned. The resistor value depends on your
test equipment. If you have a 50 ohm source, start with maybe 450 ohms to
give a ten to one ratio. The voltage drops as you approach the resonant
frequency. I've used this method for almost 50 years to identify the SRF
frequency of inductors, as well.
You can also use this method to pre tune an RF circuit before powering it
up. It puts you close to the ideal settings. I'm a retired Broadcast
Engineer.

Hello all. Is there any documentation someone can point me to that details how to test coaxial traps (I am building ones for 40m & 80m) using a NanoVNA?

No mention of who builds it, who does the firmware, software that it
is compatible with ...

Hi
I don't know,
I. Got my one from banggood and it arrived in the UK in 10 days,
And a great price,
Dave

YZTERA SV4401a 7 inch Touch LCD 50khz 4.4ghz Vector Network Analyzer
Found on Amazon.

I was able to ship a completed Norcal 40a board complete with potentiometers and connectors to Turkey for $11.40 cad using Canada Post surface mail. The package weighed in at 225 grams.
Totally untracked however. Hopefully it arrives soon.

I've had relatively few problems with my Aliexpress purchases, and Aliexpress has always found in my favour for those occurrences with a refund. It's a PITA to navigate their complaints system...

73 de Russ, va3rr