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I saw in this video the other day at 1:40:



The presenter talks about using a length of 75 ohm cable inline to
match a (theoretically) 300 ohm folded dipole to (presumably) 50
ohms. Has anyone else ever heard of doing that?

It sounds like it might be easier than using the 1/2 wave phasing coax
balun method, especially at 1 to 2 GHz frequencies, where tweaking the
antenna can require a lot of adjustments to the 3" to 6" coax loop.

I saw in this video the other day at 1:40:



The presenter talks about using a length of 75 ohm cable inline to
match a (theoretically) 300 ohm folded dipole to (presumably) 50
ohms. Has anyone else ever heard of doing that?

It sounds like it might be easier than using the 1/2 wave phasing coax
balun method, especially at 1 to 2 GHz frequencies, where tweaking the
antenna can require a lot of adjustments to the 3" to 6" coax loop.

Did a stupid. I was measuring an antenna and left the VNA connected to the feed line while I went off and did something else for a bit. My automatic message system kicked off and transmitted from a different antenna pouring 100 watts into the aether. The antennas were close, parallel in fact.

When I came back to the VNA, I found that I couldn't calibrate it. The display showed traces all over the place instead of the nice straight lines you get after calibration. I guess I may have bricked it but would re-loading the firmware correct the issue? I hate to dig into it because it is a "real" nanoVNA-H with the nice plastic case and kinda tough to break into. I suspect that repairing it wouldn't be worth the trouble since a new one is so inexpensive.

Moral of the story: turn off all RF sources while using the VNA and disconnect it if you walk off to do something else.

On Mon, Nov 2, 2020 at 08:06 AM, schweppe wrote:

Disconnect your antenna and leave the koax open. Then measure the
reflexion factor in dB at the other side of the koax. The loss in koax
is now half the reading of the reflexion factor at each frequency.

You do get 'ringing' (reflections) right across the frequency range when you measure coax loss using just the S11 reading. So you will get a large variation depending on whether the far end of the coax is open or short. You can use either a short or an open(either is fine) so long as you take into account this 'ringing'.

This graph will shows this 'ringing' and so shows what it looks like and shows the two different S11 readings, one for open coax and one for short coax. At the low frequency end (left) their basically 180 deg out of phase, but then change to almost in-phase at the high frequency end (right). I added a coax loss graph (top right) that removes the 'ringing' and shows a readable coax loss from both a far end open or short (same result from either/both), it also shows the short/open end impedance on the bottom right graph and the coax length on the bottom left graph ..

Hi All,

I am a new owner of the nano vna and i am not really sure how to read the results of the plots.
Originally i had just strung up a random wire between my garage and back fence and i have
since been playing with a Gypsy antenna i ordered off alliexpress.

Ant1 is the gypsy unit and i should note that i don't have the feed point exactly center so its more like an offset center
feed at the moment

Ant2 is my end fed random wire

For Ant1 the antenna has a 1:1 balon connected to the 2 wires of the antenna and i have 50ft of rg58au between that and the radio
For Ant2 i have a random wire with the center conductor of a piece of coax attached to the wire and the shield of coax is connected to a copper ground rod outside

here is what i don't understand

with Ant2 i can hear a time signal at over 9 s units on USB at 3.330.00 Mhz and i can hear all my local AM radio stations loud and clear.
with Ant1 i cannot hear local AM stations at all and can just barely hear the time signal at the freq above.

My rig is TS-440s

Is it possible i messed up the connectors on the coax, i would have expected the new ant to preform better but is does seem to be way worse than a random piece of wire.

In both case the wires are about 50 to 60 feet long and only running about 6 ft off the ground.

Can someone explain the data in the pictures is there any info in it that would tell me why the gypsy cannot even receive a local AM station i would have though it would at least do as well as the random wire which is just a length of 12v power wire that is stranded that i had in my junk box.

I can provide more info in need any help would be appreciated

73 de VE3SJK

Is it possible all the loss is in the coax itself i did the connectors myself and its been many years since i did one, the cable i used was stuff off of amazon. I am going to try and install the nanovna on my Ubuntu notebook and take a reading at the antenna with a short jumper to the vna and measure the antenna itself sure sounds like it was a waste of money other wise but i can still use the wires. I also wonder it this is due to the fact the 1:1 is not on centre of the span either. I am trying to find my best layout for an antenna in my back yard but its almost impossible for me to use an antenna that is centre fed the yard is 60ft wide and i have 97 feet from back of house to 6ft fence the house is 30 feet high i was thinking of some kind of end feed wire that sloped from the house to the 6ft wood fence in the back. I have also ordered a 100ft length of rg8x with the connectors done at factor should have it in a day or so to compare readings. Pretty new to HF the kenwood TS-440 is the first all band unit for me.

Hi All,

I am a new owner of the nano vna and i am not really sure how to read the
results of the plots.
Originally i had just strung up a random wire between my garage and back
fence and i have
since been playing with a Gypsy antenna i ordered off alliexpress.

Ant1 is the gypsy unit and i should note that i don't have the feed point
exactly center so its more like an offset center
feed at the moment

Ant2 is my end fed random wire

For Ant1 the antenna has a 1:1 balon connected to the 2 wires of the
antenna and i have 50ft of rg58au between that and the radio
For Ant2 i have a random wire with the center conductor of a piece of coax
attached to the wire and the shield of coax is connected to a copper ground
rod outside

here is what i don't understand

with Ant2 i can hear a time signal at over 9 s units on USB at 3.330.00
Mhz and i can hear all my local AM radio stations loud and clear.
with Ant1 i cannot hear local AM stations at all and can just barely hear
the time signal at the freq above.

My rig is TS-440s

Is it possible i messed up the connectors on the coax, i would have
expected the new ant to preform better but is does seem to be way worse
than a random piece of wire.

In both case the wires are about 50 to 60 feet long and only running about
6 ft off the ground.

Can someone explain the data in the pictures is there any info in it that
would tell me why the gypsy cannot even receive a local AM station i would
have though it would at least do as well as the random wire which is just a
length of 12v power wire that is stranded that i had in my junk box.

I can provide more info in need any help would be appreciated

73 de VE3SJK

Amazon has them, and if you want you can easily return them
AC6K
On Sun, Nov 1, 2020 at 10:38 AM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

On Sun, Nov 1, 2020 at 10:07 AM, vincent coppola wrote:

I have a NanoVNA which I love but now it's time to upgrade to a Nano

VNA-H.

Can someone please recommend a trustworthy site Thanks... Vin

Do you mean the nanoVNA-H4? I would not even consider a 2.8" screen
NanoVNA-H now that 4" models only cost slightly more. In addition to the
larger display the -H4 has better RF performance and there is better
firmware available.

Roger