108 with a hat

[nfsus]

So I am thinking about a cap hat or a bent tip on a 108 mobile whip. Found this link and read about it some. I have a good match as it is, but I wonder about using it to maybe pull the signal to the top of the antenna more than to just using it to match a shortened antenna.

http://www.antentop.org/w4rnl.001/mu8a.html

Has anyone tried the bent method? Wind drag is the issue with the hat to me but the bend would relieve that. And would a bent tip actually improve my signal to noise ratio?

 

[freecell]

from the link you posted:
"The elements for the proposed Yagi were just under 75% of full size."

there is absolutely no need for a capacitance hat on a full size 1/4 wl. antenna.

 

[Captain Kilowatt]

So I am thinking about a cap hat or a bent tip on a 108 mobile whip. Found this link and read about it some. I have a good match as it is, but I wonder about using it to maybe pull the signal to the top of the antenna more than to just using it to match a shortened antenna.

http://www.antentop.org/w4rnl.001/mu8a.html

Has anyone tried the bent method? Wind drag is the issue with the hat to me but the bend would relieve that. And would a bent tip actually improve my signal to noise ratio?

All you are going to do with a cap hat on a 1/4 wave is screw up the resonance point and end up changing the length thru cut and curse.....I mean cut and try method. Forget the idea.

 

[freecell]

now if you are still determined to follow through with this then you'll need to start out with something that is shorter than a 1/4 wl. and i don't mean just a couple of inches. the whip at half of its physical length would be as good a place as any to begin, @ 54 inches. now you can use a capacitance hat.

generally speaking, if you do a good job of it, you will end up trading down from this:

Quarter-wave full size
Rrad = 36 Ω
Rground = 15 Ω
Zfeed = 51 Ω
Eff = 71%
Loss = -1.5 dB

to this:

Top-loaded vertical (capacitance
hat or horizontal T wire) λ/8 size
Rrad = 18 Ω
Rground = 15 Ω
Zfeed = 33 Ω
Eff = 55%
Loss = -2.6 dB

Loss is referenced to a full size 1/4 wl. @
100% (ideal) antenna radiation (Eff) efficiency.

for additional information:

1974 The ARRL Antenna Book
(PDF File size: Very Large File - 41.1M)
https://www.smcelectronics.com/DOWNLOADS/1974-ARRLANT.PDF

 

[The DB]

So I am thinking about a cap hat or a bent tip on a 108 mobile whip.

The last few editions of the ARRL antenna book give directions and formulas on finding the size of a T type capacity hat. If you have any it might be a good place to start.


The DB

 

[nfsus]

102" on ball. Added small horz copper stinger at tip. Kept adjusting till it came here. It's not a true hat. Nowhere near it. More of a 90degree bent top.

 

[nfsus]

Now grant it, it's not to size. I need to order a shaft adapter to replace the ferrel that has stripped threads on different antenna. But the horz stinger shifted the readings more than the same length standing vertical. It's something to monkey with

 

[freecell]

when you find the operating frequency (below 27.200 mhz.) where J = 0.00 let us know.

 

[fourstringburn]

A caphat on a mobile antenna is used to decrease the inductance needed to match the antennas feed point that is inherent using a shortened antenna.

The inductor is the loading coil and when using a shorter non 1/4 wave antenna for any given frequency, the more coil turns needed for a match. However, the more turns on a coil, the more loss there is. So this is the trade off for running a shortened antenna.

For us running mobile 100 watt Ham rigs, the losses are significant to where we are in single digit wattage ERP to milliwatts on lower bands like 80 and 160 meters. This is because a lot of coils is needed to match a very low impedance feedpoint. A caphat on these bands can be an improvement.

A 102 whip has no loading coil but the antenna feedpoint isn't 50 ohms so there is a bit of current loss. A properly designed shunt coil would fix that but it isn't likely to make a difference in performance but it'll satisfy perfectionist.

A cap hat would be useless on a 102 whip.

Here's my HF screwdriver antenna with a cap hat. Look how much coil can be extended! The cap hat let's it use half the coil on some bands compared to without it.

 

[freecell]

the shorter the antenna is relative to a full 1/4 wavelength, especially @ the low end of the hf band, the lower the (single digit) radiation resistance. no surprise when you take into consideration that a full size 1/4 wl at 1.9 mhz. is almost 130 feet.

 

[nfsus]

when you find the operating frequency (below 27.200 mhz.) where J = 0.00 let us know.

Couldn't say. It's all new to me. Swr is all we used to use back when. Learning now

 

[freecell]

just lower the set tuning frequency 10 khz. @ a time until J = +/- 0.00. that set frequency is the resonant frequency of the antenna. if you don't have a copy of the users manual let me know.

 

[nfsus]

Never did. Got the nova and assorted hardware. That's all. Dumbing my way through.

So I guess tomorrow I need to set freq on the nova then adjust antenna untill x=0 on the set freq? Just dawned on me that x is joules? After that then match resistance? How does the phase reading play into this? I bumbled through using only the swr and resistance so far.

 

[freecell]

here you go.

https://nanovna.rf.pl/Manuals/NanoVNA-User-Guide-English-reformat-Dec_9-19.pdf

 

[nfsus]

when you find the operating frequency (below 27.200 mhz.) where J = 0.00 let us know.