102" whip vs the rest

[Beetle]

were you down here 4 vacation? you stay Hawaiianizes.

No, that was back in 1974. I'd just changed jobs with Civil Service (Navy Dept). I'd been working at the new place for a week before they sent me and several other "Ship Surveyors" to Pearl Harbor for a pre-overhaul shipcheck.

They put us up in a really nice hotel on Lewers St., between Kalakaua and Waikiki (a 30-second walk to the beach). The ship, however, wasn't in port when we got there! We were instructed to get the information that our counterpart group at Pearl had for us, and wait there a WHOLE WEEK for the ship to return! The per diem rate in Honolulu at that time was $24/day; even God Himself couldn't spend that much. We got the stuff from Pearl, divided it up by trade (I was electrical/electronics), and we spent at least eight, and sometimes as much as twelve, minutes a day looking through it. The rest of the time we were becoming "acculturated"...looking for the perfect mai-tai. I think I found it one evening but I forgot where...

 

[15minigrass]

Dang, I was only 2 years old.

No, that was back in 1974. I'd just changed jobs with Civil Service (Navy Dept). I'd been working at the new place for a week before they sent me and several other "Ship Surveyors" to Pearl Harbor for a pre-overhaul shipcheck.

They put us up in a really nice hotel on Lewers St., between Kalakaua and Waikiki (a 30-second walk to the beach). The ship, however, wasn't in port when we got there! We were instructed to get the information that our counterpart group at Pearl had for us, and wait there a WHOLE WEEK for the ship to return! The per diem rate in Honolulu at that time was $24/day; even God Himself couldn't spend that much. We got the stuff from Pearl, divided it up by trade (I was electrical/electronics), and we spent at least eight, and sometimes as much as twelve, minutes a day looking through it. The rest of the time we were becoming "acculturated"...looking for the perfect mai-tai. I think I found it one evening but I forgot where...

 

[N5ELY]

Currently I am running 102-in whip running a two pill 2290s Galaxy dx86v 5 watt low dead key and 15 watt dead key on high.

If you want to run the amplifier with 102 inch you need to add a heavy duty spring to make it 108 inch grand total with the bracket adapter.

This will drop your swr's to 1.0 swinging about 1.3 with amp on
1.1 swinging 1.4 on high with amp on.
You will see higher swrs with an amplifier without the heavy duty coil spring.

I have ran my predator 10K against this 102-in whip. They are very comparable when it comes to performance it's hard to decide which one is better. The predator 10K is lightweight aircraft aluminum. I personally think that predator 10K has a better receive. It seems more sensitive. But then again I will tell you the 102 inch whip I've had a whole lot better luck getting out further this is like a skip shooting antenna. Especially if you tilt it forward. There's a comment on this page that they say 102-in whip will make your swords go crazy when the winds blowing. That is nothing but disinformation. My radio calibrates SWR and when I'm driving with the coil it doesn't affect the swrs at all.
There is another guy that said he was hearing things on the predator 10K the 102 inch whip wasn't hearing and I will definitely agree with that. But I will say very clearly I've had more luck hitting skip with this 102-in whip and then the predator 10K. I haven't actually done the testing and I'm really curious to actually try. But to actually know which one is truthfully better I would have to buy the predator 10K and actually perform a test and come back to this page and let y'all know what the results are.

Back when I had a predator 10K I had the two pill 2290s push in a four pill competition box with a 2879 s.

The aluminum shaft of the predator 10K was hot as hell. When putting a thousand watts in the antenna. The 102 inch whip does not feel hot when I'm transmitting on it for a while. The predator 10K had more background static you would hear people far far away breaking your squelch.

The 102 inch whip I don't hear anyone breaking my squash even with a squash turned all the way down I don't hear anything. But I have talked to people that told me my signal is getting out.

 

[AudioShockwav]

Back when I had a predator 10K I had the two pill 2290s push in a four pill competition box with a 2879 s.

The aluminum shaft of the predator 10K was hot as hell. When putting a thousand watts in the antenna. The 102 inch whip does not feel hot when I'm transmitting on it for a while.

I have dumped over a kw into a single coil p10k without a problem many times.
I don't get the part about you need a spring to run a amp.
Do you take the spring off when you don't run your amp?


73
Jeff

 

[Dopple]

Interesting article... granted, it's for VHF, so the size of the ground plane being the same, but the frequency being lower, the effects might be more dramatic. I haven't modeled it for HF freqs.

5/8th wave mobile antenna vs 1/4 wave

5/8th wave compared to 1/4 wl antenna

www.w8ji.com

 

[The DB]

Good article, but there is nothing in it that hasn't been discussed and modeled by Marconi and I on this forum at CB frequencies in the past.


The DB

 

[Alexis Mercado]

I have a 1999 Montero Sport SUV. I plan to go to a keydown competition next July. I plan to use a 4 pill amp ( 1,200w pep ) with a Motor Maul and a 102” whip. Since I am not using an antenna puck ( don’t want make a hole on the roof ) I will be using a magnetic mount with a heavy ground strap grounded to the rear gate hinge.

When I tried to tune the whip, I couldn’t. I installed the heavy duty spring with no avail. I tuned around the 30 MHz. I installed a Wilson SS 10” shaft. It tuned around 26.100 MHz. Raised the rear gate and tuned around 27.000 MHz with an SWR of 1.1 at 51 ohms.

With the 10” shaft and the HD Spring, the total length is 117” .

How come is this ? A 1/4 wave whip should be 109”. Are those 117” detrimental or advantageous?

 

[brandon7861]

I run a triple mag mount base loaded 84" whip (had to cut the 102 down so it didn't hit stuff) on the cab of my silverado and it gets out to my local friend as good as my sirio827 at the house. He also has a sirio827 at home. I can talk to him in my truck for 25 miles in fairly hilly and wooded terrain before I start to lose him. It seems to work better (maybe lower pattern) than it did before I cut it and loaded it. We also put a 102" on the top center (custom steel rack mount with ground strap) of my friends 2003 trail blazer and I think my shorter antenna has him beat by a good 2 s-units locally running the same power. And my shortened mag mount works just as good on our 2005 buick lasabre, so I didn't just get lucky cutting it. There is something special about that beast. One day Ill have to walk around it with a field strength meter...

 

[Alexis Mercado]

I have a 1999 Montero Sport SUV. I plan to go to a keydown competition next July. I plan to use a 4 pill amp ( 1,200w pep ) with a Motor Maul and a 102” whip. Since I am not using an antenna puck ( don’t want make a hole on the roof ) I will be using a magnetic mount with a heavy ground strap grounded to the rear gate hinge.

When I tried to tune the whip, I couldn’t. I installed the heavy duty spring with no avail. I tuned around the 30 MHz. I installed a Wilson SS 10” shaft. It tuned around 26.100 MHz. Raised the rear gate and tuned around 27.000 MHz with an SWR of 1.1 at 51 ohms.

With the 10” shaft and the HD Spring, the total length is 117” .

How come is this ? A 1/4 wave whip should be 109”. Are those 117” detrimental or advantageous?

Any idea regarding this ?

 

[brandon7861]

Any idea regarding this ?

Adding length beyond 1/4 wave makes it inductive, so i suspect that when the gate is lifted, the added capacitance cancels the inductance and brings it closer to resonance (not necessarily 50ohm though). Do you have a VNA/antenna analyzer?

 

[Alexis Mercado]

Adding length beyond 1/4 wave makes it inductive, so i suspect that when the gate is lifted, the added capacitance cancels the inductance and brings it closer to resonance (not necessarily 50ohm though). Do you have a VNA/antenna analyzer?

Yes I do

 

[brandon7861]

Yes I do

It would be possible to make a matching network at the base of the antenna. If that is something you are interested in doing, I would need to know the antenna feed point impedance, and that would raise a few more questions as I want to be sure it's done right (no offense intended at all, most people just use their fancy analyzers as SWR meters and throw the principles of RF signal integrity out the window once they are at the antenna).

What type of VNA do you have? I am asking because some analyzers don't tell you the sign of the reactance (MFJ) and some don't do OSL calibrations on the unit itself (older RigExperts). If you have the means to calibrate the unit, do you have an OSL kit that fits the other end of the coax at the antenna end (SO-239) or just one that fits the VNA port? If the latter is the case, that's ok, it just adds a step (measuring coax electrical length). Where is the antenna mounted? Center, corner top, bumper (I really hope not for a competition)? Are you good at custom work (like getting some heavy copper wire and making a coil and possibly mounting a different SO-239 for tapping the coil? Are you opposed to cutting some of the whip off if needed? I'd love to see some pictures.

 

[Alexis Mercado]

brandon, I’ll post some pictures in a couple of days. I have a Mini 1300 analyzer.

Thanks for responding.

 

[Alexis Mercado]

Here are some pictures of the analizer results with the rear gate opened ( I forgot to take a picture of gate opened )

First picture is with the gate opened and with the meter and amplifier in line. Second one is only cable and antenna and gate opened. The third one is with the gate closed with a 97.5” long aluminum radial.

Best results are with the radial.

Brandon says: If you have the means to calibrate the unit, do you have an OSL kit that fits the other end of the coax at the antenna end (SO-239) or just one that fits the VNA port? If the latter is the case, that's ok, it just adds a step (measuring coax electrical length).

Answer is: I have the OSL kit that fits the VNA port. When I bought this analyzer, I calibrated it because I read on the instructions manual I had to do so.

 

[brandon7861]

Here are some pictures of the analizer results with the rear gate opened ( I forgot to take a picture of gate opened )

First picture is with the gate opened and with the meter and amplifier in line. Second one is only cable and antenna and gate opened. The third one is with the gate closed with a 97.5” long aluminum radial.

Best results are with the radial.

Brandon says: If you have the means to calibrate the unit, do you have an OSL kit that fits the other end of the coax at the antenna end (SO-239) or just one that fits the VNA port? If the latter is the case, that's ok, it just adds a step (measuring coax electrical length).

Answer is: I have the OSL kit that fits the VNA port. When I bought this analyzer, I calibrated it because I read on the instructions manual I had to do so.

More questions...

1) How did you attach that ground strap to the mag base? Did you peel the foil off? That foil had a purpose which I'll get to shortly.

2) Why not put the antenna in the middle of the roof? If you are going to a competition, that's where you want it. I could see if you were just shootin' the s#!t on the freeway for 10 miles, but for a competition, you really want it in the middle of the roof. I'm going to catch heat for this, but if the ground strap is the only reason for putting it on the back, abandon that plan. You can ground 27MHz without metallic contact.

3) Are you willing to venture outside of your comfort zone and make some serious changes? If so, keep reading...


In order to have a chance at the competition, I would recommend you move the antenna to the center of the roof, but before doing so, we need to do a few things.

Being you have a mount that the coax cannot be easily removed from, we need to measure the electrical length of that coax MacGyver style before we take any antenna impedance measurements. To do this, remove the antenna from the vehicle, remove all antenna parts from the mag base, short the antenna mounting stud to ground with as short of a wire/strap as possible (or, preferably underneath where the coax braid/center conductor are exposed since the foil is already gone), then set it on a stump or other non-metallic surface and see what the lowest frequency is that the impedance is closest to zero. This will be the frequency at which the coax is 1/2 wavelength long. And knowing that, we can calculate the antenna feed point impedance from the impedance measured at the other end of the coax once it is back on the roof, but not yet.

Now we need to talk about grounding... Since you do not want to drill holes, we need capacitive coupling (which works fine, don't let anyone convince you otherwise). I understand your antenna has only one magnet, but for sake of discussion, lets consider a mount that has three magnets (you'll see why soon), each of 3" diameter. That comes out to about 21 square inch magnet surface area. With the average paint thickness of 0.1mm (not considering the dielectric of the paint as that only makes this math better), we have a capacitive reactance of 5Ω at 27MHz. Essentially, a short to ground (now you know what that foil was for ). So, if we can use foil tape connected to the ground screw under the mag mount (or plain aluminum foil with two more magnets holding it tightly to the roof) right under the antenna, we have our ground and running that strap all the way to the hinge is completely unnecessary.

Ok, so now we know the electrical length of the coax, we have the antenna positioned properly in the center for best pattern, and we have it grounded to the center of the roof. Now we can screw the whip back on and take a measurement of the antenna itself. Do this at the frequency you intend to use the antenna on, don't center the VNA where the SWR is lowest, we don't really care about that for this step.. Once we know what the feed point impedance is at the antenna (compensating for the coax length we measured earlier), we can make adjustments and design a matching solution based on math rather than trial and error. Once we have that number , we can talk about what needs to be done at the antenna itself to get the SWR down.

Ill stop here for now. Are you still on board with the process?