Steel Whip Info

[Mudfoot]

MFJ sold two versions. One is 102" and the other was 108". Not sure if they still have them. They probably do.

 

[Blackcat630]

MFJ 1966 dx engineering says no longer available. Giga parts says the same... but also says pick up only, does not ship. So maybe someone has stock and just doesn't want to hassle with shipping? This is the model I bought several years back. My old car is gone but the 108 and the breedlove ball are in the shed.... maybe one day I'll break em back out?

 

[2NC995]

Just for giggles I connected my NanoVNA to my 102" antenna to see the results. I set it up for 26 - 28.5mhz. I had built it using only a SWR meter.

I planned to post pictures, but that's not going to happen in the sun, and I haven't yet connected it to a PC.

Results:

- Lowest SWR = 1.11 at 27.425
- The SWR curve is not symmetrical - it rises faster below that frequency than above.
- 1.5 or better SWR from 26.475 to beyond 28.5 (which is 1.36)
- X = 0 at ~ 27.525
- Lowest return loss at 27.525 (-25.86db)

I'm only beginning to use this device so don't necessarily understand this 100%...but the antenna is certainly working well for me.

 

[Slowmover]

MFJ 1966 dx engineering says no longer available. Giga parts says the same... but also says pick up only, does not ship. So maybe someone has stock and just doesn't want to hassle with shipping? This is the model I bought several years back. My old car is gone but the 108 and the breedlove ball are in the shed.... maybe one day I'll break em back out?

I ordered a pair last year (102”). Was sent in a flexy PVC tube of a small diameter.

 

[M0GVZ]

Just for giggles I connected my NanoVNA to my 102" antenna to see the results. I set it up for 26 - 28.5mhz. I had built it using only a SWR meter.

I planned to post pictures, but that's not going to happen in the sun, and I haven't yet connected it to a PC.

Results:

- Lowest SWR = 1.11 at 27.425
- The SWR curve is not symmetrical - it rises faster below that frequency than above.
- 1.5 or better SWR from 26.475 to beyond 28.5 (which is 1.36)
- X = 0 at ~ 27.525
- Lowest return loss at 27.525 (-25.86db)

I'm only beginning to use this device so don't necessarily understand this 100%...but the antenna is certainly working well for me.

What is the value of R where X=0? This tells you how effective your RF ground is. A 1/4 wave antenna over a perfect ground should give a R value of 36.8 Ohms where X=0. Anything away from that is a less than perfect ground and you have ground losses which can effect performance.

If you read the page on bonding at www.k0bg.com and apply that to your vehicle you should see the value of R change more towards 36.8 Ohms however depending on how and where you mount the antenna you may not be able to reach that. What you should also see change if you don't alter the length of the antenna is the frequency where X=0 drop as your RF ground improves.

 

[2NC995]

What is the value of R where X=0? This tells you how effective your RF ground is. A 1/4 wave antenna over a perfect ground should give a R value of 36.8 Ohms where X=0. Anything away from that is a less than perfect ground and you have ground losses which can effect performance.

If you read the page on bonding at www.k0bg.com and apply that to your vehicle you should see the value of R change more towards 36.8 Ohms however depending on how and where you mount the antenna you may not be able to reach that. What you should also see change if you don't alter the length of the antenna is the frequency where X=0 drop as your RF ground improves.

Thanks for the input. I thought I’d snapped a shot of the resistance plot, but I’m not seeing it. I’ll have to take a look this afternoon away from the house and other cars.

 

[bob85]

i used to use the same copper pipe setup as the pic for dx in the car
started out as a 2 piece fat antenna but that was too top heavy & caught too much wind,

made an aluminium version from vector 4000 tube & loaned the copper to a buddy who bent the top section with his motorbike,
replaced top section & loaned it to another buddy who backed over it with his van before trying it, RIP,

don't lean stuff against your van then jump back in to back up a little because its 1ft higher.

 

[2NC995]

What is the value of R where X=0? This tells you how effective your RF ground is. A 1/4 wave antenna over a perfect ground should give a R value of 36.8 Ohms where X=0. Anything away from that is a less than perfect ground and you have ground losses which can effect performance.

56ohms at x=0. So, I suppose not great, but it sure makes the SWR look good.

It should be said that I’m not checking at the feed point. That would be under the headliner and I’m checking through approx 12’ of coax.

 

[M0GVZ]

56ohms at x=0. So, I suppose not great, but it sure makes the SWR look good.

It should be said that I’m not checking at the feed point. That would be under the headliner and I’m checking through approx 12’ of coax.

That'll explain it then. You could use a half wave length of coax (remembering to take into account the velocity factor of the coax) and that would give you readings very close to what it is at the feedpoint but as it's working and you're not getting common mode issues there's little point.

 

[Marconi]

It should be said that I’m not checking at the feed point. That would be under the headliner and I’m checking through approx 12’ of coax.

Dan, I don't know your mobile or coax specs, but I think your feed line at 12' feet could already be very close to a resonant 1/2 wavelength...assuming the coax Velocity Factor (VF) is 0.66% of course. Just a guess.

Here is a link to a simple 1/4 wavelength ground plane description by "Electronics Notes dot com." I can't say this is the theoretical bases of M0GVZ's theory for R = 36.8 ohms @ X = 0.00 ohms reactance, but it looks to me to be close. "EN" did not show all the values. I used this source because it looks close to the model I made below, with the exception this is constructed similar to a coaxial ground plane. This might be the cause of the slight difference we see in results.

https://www.electronics-notes.com/a...n/vertical-antennas/quarter-wave-vertical.php

The PDF file below shows my model of a simple 1/4 wave ground plane with horizontal radials at 27.205 MHz. This model produces R = 38.77 OHMS, with X = 0.05846 ohms which is very close to M0GVZ's comments above. Here I assume the theory was calculated or measured very close to the ground. My model is 1" inch above ground. I also set the radiator and radial to equal lengths and then adjusted them all...until the reactance was equal to X = + J 0.05846 ohms as noted.

If I took this 105.503" whip and put it over a mobile model...I doubt I would ever see the theoretical 36.8 ohms @ 0.0 ohms at the feed point without changing the dimensions.

So, let's consider my model is wrong. Maybe you could check your match using your new analyzer and see if you can find a match at some frequency where the results are equal to the theory. Then, maybe you can let is know what frequency you end up at.

I'm not saying that the theory 36.8 ohms @ 0.0 oms is wrong, IMO it is just misapplied when we start looking for similar results on a mobile installation...where the ground plane etc. is so, so, so, different.

 

[2NC995]

I'm not saying that the theory 36.8 ohms @ 0.0 oms is wrong, IMO it is just misapplied when we start looking for it on a mobile installation where the ground plane is so, so, so, different.

Thanks for your input. Yeah, I don’t think I’m going to see 36.8 ohms on my truck no matter what I do, simply because it’s not the right shape.

I was thinking: with a quarter wave antenna using angled radial to reach 50 ohms, is the antenna worse off than before? It doesn’t seem like it would be, and if not then 50 ohms should be good for me, too, so long as I’m not compromising reactance to get there?