DB 201

[n4dbm]

That is interesting on the match with the Arrow GP146. It's about as simple of an antenna as you can get, and the ground radials bent at a 30-degree angle should give a near perfect match wherever the radiating element is resonant. How much cable and what type of cable did you have between the antenna and the analyzer? The analyzer or meter should be as close as possible to the antenna as it can be. Theoretically, if everything between the analyzer and the antenna is exactly 50 ohms, it shouldn't matter. But that's never the case, and certain lengths of cable between the antenna and analyzer can and will throw readings off, sometimes badly. Regardless, the extra length in your new radials and keeping them at 90 degrees from the radiator making the match "better" is interesting. I don't have a good answer for what's going on there.

Second, the reason most 1/4 wave through-hole mobile antennas match decent with the metal being at a 90-degree angle is due to the amount of metal under the antenna, as it's not just four wires, but it's A LOT of metal. So, instead of resonant radials making up the "mirror" part of the antenna, the car's sheet metal is acting as a true ground plane.

The YouTube video link is neat, but that's a very weak antenna design. I'm certainly not throwing off on the builder at all, because I have built plenty of mechanically weak antennas for experimental and learning purposes. But, actually making this and expecting it to survive for any length in the great outdoors is ridiculous. It is beyond mechanically weak, especially with soft drawn copper. The radials at that angle with that kind of mass will droop down very quickly under its own weight. If you want to build something like this for learning purposes, then by all means do so. When you've got your initial thrill from your build, fold all the radials straight down. This will now make your antenna a half-wave. The impedance will be close to 100 ohms, and give you a 2:1 VSWR. To correct this, an odd electrical 1/4 wavelength of 75 ohm cable will transform the 100 ohms into very close to 50. You will just have made a "sleeve dipole" antenna, very similar to the popular DB Products DB-205.

If you are going to stick with a 1/4 wave, at least opt for 3/32" bronze welding rod for strength and rigidness. Also be sure to seal the SO239 connector with hot glue or silicone. If you're going to hang the antenna from a rope like the video, use a good glass insulator. The tip end of a 1/4 wave is a very high voltage point and using wood or some plastic blends will not only detune the antenna, but seriously decrease performance on transmit.

As far as match versus performance, a 2:1 match is 11% reflected power. In a practical setting, no one on the other end will see the difference in a 2:1 versus a 1:1 match. It will just be less heat dissipated by your final amplifier device.

Good luck on your project.

 

[ind224]

The ones that got away when they demoed the old terminal at KIND. Having spent much time prior to 9/11 parked on the top of the garage watching approaches to 23L and R and looking at all those antennas including 3 C bands on non penetrating mounts.
Long story short I told him I wanted it all. It was the best scenario for me: they could get them all down and intact, I'd offer a lump sum for the lot. He called me after they got the dishes down but had not taken the antennas down so I told him to call me back when they had everything together and he never called me back and never answered my calls again. My guess is he figured they had some value.....

 

[KA0XR]

The ones that got away when they demoed the old terminal at KIND. Having spent much time prior to 9/11 parked on the top of the garage watching approaches to 23L and R and looking at all those antennas including 3 C bands on non penetrating mounts.
Long story short I told him I wanted it all. It was the best scenario for me: they could get them all down and intact, I'd offer a lump sum for the lot. He called me after they got the dishes down but had not taken the antennas down so I told him to call me back when they had everything together and he never called me back and never answered my calls again. My guess is he figured they had some value.....

Wow, thanks for posting these cool rooftop pics and your story about attempting to 'rescue' some DB-201's! If anything it's too bad you couldn't at least get the heavy duty brackets. If they weren't scrapped wonder where they ended up or if put back into service? Looks like a DB-222 or 224 in one of those photos as well.

 

[ind224]

Yes, the 224 was very tall you see 25%. This was the mother load.

 

[n4dbm]

Good photos, thanks. All of the folded monopole antennas you have posted except for the one in DSC01117 are Phelps-Dodge models, NOT Decibel Products. The one in DSC01117 is definitely a Decibel Products DB201, and a more recent model at that. The "newer" ones did away with the split center shaft with two bolts on each side and went with a hex shaped bottom sleeve with small set screws in the sides.

All of the other ones as I mentioned are Phelps-Dodge, or maybe Celwave, if Celwave carried over production of these which I think they did. The model number is PD128. The biggest difference you can tell is where the 3/4" tube converts over to 3/8" rod at the top, the welds are not tapered, but immediately convert from the bigger tube to the smaller rod. Also, the center insulator is not an epoxy resin type material like the DB-201 uses, but it is ceramic! Will definitely hold up in the weather! Both of these antennas terminate into a 1" FPT. That's a bummer you were not able to get these. Here's some info on the PD128's from Wisco. They aren't in production anymore, so Wisco really needs to update their page.

WISCO International (CELWAVE - PD128) (wiscointl.com)

The bottom element in DSC01116 is from a Decibel DB264, not a 224. The 264's have enclosed feed harnesses and were most popular in the 155-165 versions and the 164-174 as well (FBI, ICE, government). The biggest problem with those antennas is where the little white insulator piece on the element is gets weathered pretty bad and turns into a chalky material over 20 years.

73, N4DBM.

 

[KA0XR]

Good photos, thanks. All of the folded monopole antennas you have posted except for the one in DSC01117 are Phelps-Dodge models, NOT Decibel Products. The one in DSC01117 is definitely a Decibel Products DB201, and a more recent model at that. The "newer" ones did away with the split center shaft with two bolts on each side and went with a hex shaped bottom sleeve with small set screws in the sides.

All of the other ones as I mentioned are Phelps-Dodge, or maybe Celwave, if Celwave carried over production of these which I think they did. The model number is PD128. The biggest difference you can tell is where the 3/4" tube converts over to 3/8" rod at the top, the welds are not tapered, but immediately convert from the bigger tube to the smaller rod. Also, the center insulator is not an epoxy resin type material like the DB-201 uses, but it is ceramic! Will definitely hold up in the weather! Both of these antennas terminate into a 1" FPT. That's a bummer you were not able to get these. Here's some info on the PD128's from Wisco. They aren't in production anymore, so Wisco really needs to update their page.

WISCO International (CELWAVE - PD128) (wiscointl.com)

The bottom element in DSC01116 is from a Decibel DB264, not a 224. The 264's have enclosed feed harnesses and were most popular in the 155-165 versions and the 164-174 as well (FBI, ICE, government). The biggest problem with those antennas is where the little white insulator piece on the element is gets weathered pretty bad and turns into a chalky material over 20 years.

73, N4DBM.

You are the master of folded ground plane monopole antennas! Sounds like Phelps-Dodge copied the original Decibel Products design with a few tweaks. Wish the PD-128's were still in production. Thanks for the other tips you mentioned about reflected power vs. SWR efficiency and the tip end of the radiator being high voltage.

I did recently build both simple 2m and 70cm ground plane antennas out of #12 copper wire for the radials and #10 for the radiator. I couldn't find any welding rods greater than 18" at my local hardware store so I stuck with copper for the project . As expected, at least on 2m, the SWR bottoms out when the radials are bent down at 45 degrees, but is close to 2:1 with the same radials at 90 degrees. After building mine I concur that the design in the video I posted looks pretty flimsy, especially the radial attachments. I crimped my radials into ring terminals and screwed the terminals into the mount. Eventually I'll repeat the same procedure using longer welding rods and also build a folded monopole like your older how-to example.

As far as your question on my Arrow GP146, I have been testing it using my Mini1300 analyzer hooked up to a 12 foot length of RG-8x coax, bought last year as a new factory made jumper from eBay. The antenna is secured to two 48" TV antenna poles stacked together and in the open. I've checked the SWR multiple times and the SWR was near perfect 1.1 around 146 MHz each time and never higher than 1.3 at each end of the band. The radials are about 24" long and like I mentioned are sticking out at 90 degrees, so it looks like a DB-201, minus the folded radiator. When it warms up I'll hook it up to my Bird watt meter to verify the analyzer data.