Modified Vector 4000

[The DB]

My only interest is to get both of you talking about this topic, dbm measurements, that Henry presented to us back in 2014. I would also like to hear more from Henry on this topic.

Let me try a different approach.

Think about dBm as what s-meters should have been. If s-meters were actually accurate, you could directly convert s-meter readings to dBm.

s1, -121 dBm
s2, -115 dBm
s3, -109 dBm
s4, -103 dBm
s5, -97 dBm
s6, -91 dBm
s7, -85 dBm
s8, -79 dBm
s9, -73 dBm​

As we can see, each s-unit should relate to a dBm measurement that is exactly 6 dB higher than the previous s-unit. I am aware that some people who tune radios will adjust the s-units to some degree, but the ones I've seen do this will only adjust to one specific s-unit, typically s-9. Perhaps as we switch to SDR type radios over time this is an issue that might go away as SDR type receivers seem to be far better and measuring received signals. This isn't the only thing I see changing when it comes to antenna discussions in the next several years.

There is really nothing fancy about dBm measurement, as discussed it is what your radio should essentially already be showing you. It is just a measure of received signal power as compared to a specific measurement, and that measurement is 1 milli-watt. Its a standard that originates on the engineering side, originally only very expensive equipment could accurately measure using such a standard, but now many hobbyists also use it as well, and with the newer equipment that is available and quickly becoming less and less expensive over time, I think it will become more and more prevalent among the more knowledgeable people in the hobby.

It seems bob85 got a reply on this in before me... Timing is everything... lol

"Can we use the error value we get when running the AG test, and apply that error value to the reported gain for the Real Earth model to correct the overstated or understated gain reported?

Yes you can. Although if AGT is to far from 1, I have seen this error value not be correct in both freespace and over a perfect ground, so if AGT isn't close within reason to 1, I wouldn't trust this number.


The DB

 

[Marconi]

i had no idea that you did not understand what Henry's graph was showing,
i don't know how it was generated other than its a function of the software Henry uses,

Bob, I don't know how it was generated either, all I was trying to figure out was what the graph was showing us, and I seem to recall back then some discussion about page #41.

After reading about this new idea for measuring antenna signals, his image of the antenna looked like Henry was using 4NEC2. Even so, I think DB just told us his 4NEC2 report, using dbm showed him a different looking result. I could also be wrong in my recollections here too.

Right now, my only concerns about dbm measurements are; considering that Henry told me the chart was being misunderstood I sorta' forgot about it.

Later I understood somehow...that Henry warned DB to proceed with caution using the dbm feature.

And then, more recently, I think DB told us his 4NEC2 software was not working as intended and he stop using the feature.

So Bob I'm still confused. So just for grins...what are the chances you could describe what you think Henry's chart is showing us?

 

[Marconi]

Let me try a different approach.

Very good approach DB. I think maybe Bob has been talking about these same issue for a while now, but I wasn't quite getting the point,

Thanks,

 

[Marconi]

There is really nothing fancy about dBm measurement, as discussed it is what your radio should essentially already be showing you. It is just a measure of received signal power as compared to a specific measurement, and that measurement is 1 milli-watt. Its a standard that originates on the engineering side, originally only very expensive equipment could accurately measure using such a standard, but now many hobbyists also use it as well,

DB, you make it sounds so simple. When you've used your spectrum analyzer did you make any kind of record, as a reference, comparing a couple of CB antennas?

It would be interesting to see what such numbers look like and the results such a comparison shows. Maybe you could do us a video.

 

[bob85]

Eddie

Henry has more than one chart showing different things,

the chart with & without radials shows signal strength received at the rx antenna at a height of 10mtrs & sited 30kilometers from the sigma4,

across the top is the sigma4 height above ground in meters,
down the side is signal strength in dBm,

it shows that when the sigma is isolated from mast & coax,
radials increase signal strength by almost 2db when the sigma4 is 10mtrs above ground & that the radials advantage reduces the closer the sigma4 is to ground,

what part is confusing you Eddie ?.

If you want to see the software I used in action watch the video you posted with the guy testing chokes using sdruno software with his rspduo



the spectrum screen is scaled in dBm on the left & also has a bar graph s-meter,
look under the bar graph you will see dBm & snr.

 

[The DB]

DB, you make it sounds so simple. When you've used your spectrum analyzer did you made any kind of record, as a reference, comparing a couple of CB antennas?

It would be interesting to see what such numbers look like and the results such a comparison shows. Maybe you could do us a video.

I haven't, although since I got the spectrum analyzer early last year I have thought about doing something like this. I agree, it would be interesting to see what kinds of differences we would see.

The thing holding me back the most from doing this right now is, at the moment, I don't have a ton of antennas that are intended for use on the same band or the same mounting location.


The DB

 

[HomerBB]

@Marconi
I don't remember whether I ever shared the dimensions I used on my 6m V4k.
Length of vertical 177.5" from bottom of cone to tip (taper 1"×59">3/4"×35-1/4">83-1/4"×1/2")
Radials 55"×3/8"
Ring diameter 17-1/4" (1"×1/8" flat stock)
Gamma sleeve 13"×1/2"
Gamma rod 27"?×1/4" (can't recall exact length)
Gamma tap to vertical 18" above feedpoint
Dogbone on Gamma rod 3-5/8" above Gamma tube
Dogbone length outside to outside 5"

 

[Marconi]

@Marconi
I don't remember whether I ever shared the dimensions I used on my 6m V4k.
Length of vertical 177.5" from bottom of cone to tip (taper
1"×59"
3/4"×35"
1/4">83"
1/4"×1/2"
Radials 55"×3/8"
Ring diameter 17-1/4" (1"×1/8" flat stock)
Gamma sleeve 13"×1/2"
Gamma rod 27"?×1/4" (can't recall exact length)
Gamma tap to vertical 18" above feedpoint
Dogbone on Gamma rod 3-5/8" above Gamma tube
Dogbone length outside to outside 5"

Thanks for sharing what you do Homer.

What frequency did you find resonance and I'll make a 6M model?

 

[HomerBB]

I was after 52.5, if I recall. . .

 

[Marconi]

Thanks.

 

[bob85]

Homer

after some hunting around the sirio donor parts pile this morning i realised that i only have 6 full length vector lower radial tubes left

so 3/8wave cone first,
i set the hoop to 17", cone 89" & monopole to 180" as a start point,

i expect both to be a little long because im not including wavelength/diameter ratio in my scaling,

i will look to see if i have enough vector parts at my old place to make another with 1/4wave radials to speed up comparison tests.

 

[HomerBB]

Bob, I robbed some old yagi elements to make the cone radials. They didn't seem to mind.
I may have missed the best lengths with mine, but it has worked very well.

 

[freecell]

 

[Marconi]

Homer here is my model of your 6 meter Vector 4K, in Free Space, over real Earth, without common mode current mitigation, and with a choke added. I did not use taper, so I had to average the radiator diameter and used the tune for the length.

Your radiator length shows to be about 10" longer, but the radials length and the loop diameter are pretty much what you posted. I had to make the loop wire diameter 0.29. I also made a mistake on the Radial Loop detail showing the diameter as 0.16" for the loop wires. They should be 0.29" inches as you will notice in the image of the radial Loop.

 

[HomerBB]

Thanks, Marconi.
So, it appears that I should shorten the vertical, and retune the gamma to match. I should be sure to choke the feedline (but at what point? Hard to tell on model). This should optimize my antena...?