Traintenna-Is it really designed for 160-161MHz???

timkilbride · #1 (**permalink**) 11-04-2009, 05:54 PM

I picked one up at a garage sale, pulled the guts out and its only 48 3/4" long! Should be close to 53". Based on my skills, this thing is cut for 174MHz. The feed point is at 2 1/2", should be closer to almost 4. The "notch" cut is at 16" and only runs for 1/4", should be cut at 17 1/2" and run for 3/4". Are you guys really getting what your paying for?

I have attached some plans if you want to build your own. You can either make it out of 300ohm twin TV lead or 450ohm ladder line. Once made, slide it into a PVC pipe, cap the ends and you have a antenna. I bought 100 feet of 300ohm cable at Radio Shack for $20, 120" of PVC is $1.50, end caps are .50. I built one for myself that is actually tuned to 161MHz, and have been using the left over 300ohm cable making antennas and selling them. The other three pictures are the "guts" of the traintenna.

Tim K.

DPD1 · #2 (**permalink**) 11-04-2009, 06:51 PM

Sigh... First off, that is a very old one. It's made differently now. Second, yes, they are all tuned properly. We wouldn't sell something that isn't what it says it is. You are going by physical dimensions. Without using a field monitor, that means nothing. That can vary by 3" or more. You have to use a field monitor to see what is really going on. The enclosure material changes the resonance point... Numerous things can change the resonance point drastically. Even the plastic covering of a wire can change from batch to batch and change the resonance point by 2-3 MHz or more, using the sames exact wire. The size of the notch means nothing.

prcguy · #3 (**permalink**) 11-04-2009, 08:40 PM

What is a field monitor?
prcguy

Quote:

Originally Posted by DPD1

Sigh... First off, that is a very old one. It's made differently now. Second, yes, they are all tuned properly. We wouldn't sell something that isn't what it says it is. You are going by physical dimensions. Without using a field monitor, that means nothing. That can vary by 3" or more. You have to use a field monitor to see what is really going on. The enclosure material changes the resonance point... Numerous things can change the resonance point drastically. Even the plastic covering of a wire can change from batch to batch and change the resonance point by 2-3 MHz or more, using the sames exact wire. The size of the notch means nothing.

DPD1 · #4 (**permalink**) 11-04-2009, 08:51 PM

Like an Anritsu Site Master or something similar.

zguy1243 · #5 (**permalink**) 11-04-2009, 08:58 PM

I just find it interesting that you have found such a antenna at a garage sale.

timkilbride · #6 (**permalink**) 11-04-2009, 10:56 PM

Quote:

Originally Posted by DPD1

Sigh... First off, that is a very old one. It's made differently now. Second, yes, they are all tuned properly. We wouldn't sell something that isn't what it says it is. You are going by physical dimensions. Without using a field monitor, that means nothing. That can vary by 3" or more. You have to use a field monitor to see what is really going on. The enclosure material changes the resonance point... Numerous things can change the resonance point drastically. Even the plastic covering of a wire can change from batch to batch and change the resonance point by 2-3 MHz or more, using the sames exact wire. The size of the notch means nothing.

How is it made now? I find it odd all the cuts are made for 174.000MHz. I do agree enclosure material and related material change the resonance point. We still got 13MHz spread here. . .

Tim K.

timkilbride · #7 (**permalink**) 11-04-2009, 11:02 PM

Quote:

Originally Posted by DPD1

Like an Anritsu Site Master or something similar.

At 160.305 I had a SWR of 3.3:1

Tim K.

timkilbride · #8 (**permalink**) 11-04-2009, 11:23 PM

Quote:

Originally Posted by zguy1243

I just find it interesting that you have found such a antenna at a garage sale.

The guy said it didn't work well as he though it should have. He said he listened to Police/Fire in the 155MHz area, railroads/NOAA in 160-162. He went back to his old antenna. Maybe if he monitored the feds in the 174MHz area he would have liked it???

Tim K.

DPD1 · #9 (**permalink**) 11-05-2009, 12:54 AM

The dimensions are not made for 174, they are made for 160-161, as dictated by the materials and actual testing done, until the preferred results were achieved... Not by just looking at some java script or plans for making antennas on a ham web site. You don't seem to comprehend this. We've been selling thousands of products for almost 10 years now, and that includes to numerous commercial and extremely large government organizations... Some of whom independently test samples before they put in their orders, and they had absolutely no problems with anything. If products we sold were severely flawed, I'm pretty sure people would have figured it out by now. I personally test every single thing that is sold, and I would never send out anything that is flawed. I have rejected units that were just barely 1 MHz off. I have no idea how you're getting the numbers you claim and I don't really care. What would possess a person to just out of the blue, come onto a public forum with hundreds of people and try to accuse a business of somehow scamming people, when that person clearly has no idea what they are talking about, is beyond me. Normally I'm a very patient person, but I don't bust my a$$ 7 days a week trying to run the most honest, professional business I can, just to have someone accuse me of trying to scam people, because they have nothing better to do.

W9RXR · #10 (**permalink**) 11-05-2009, 07:06 AM

Dave, I have a suggestion from an innocent bystander...Relax. As a businessman, ranting in public doesn't do you any good. Keep your public comments factual and professional.

I know that SWR readings are not the holy grail of antenna design that some folks think they are. But I find it interesting that someone would report that one of your Traintennas measured 3.3:1 at the low end of the rail band. Based on your measurements, what should the SWR be? Is the antenna he has defective? Is his measurement method flawed? Is the antenna resonance being affected by something in its near field?

burner50 · #11 (**permalink**) 11-05-2009, 12:22 PM

Somebody hit a sore spot?

While I have no doubt that the plastic will alter the resonance of the antenna... I doubt the plastic will alter it 13Mhz causing the design to be modified in such a way... Hundreds of slim jim antennas are made every day using the above formulas, and they seem to work properly, but on this application the formula doesnt matter?

smason · #12 (**permalink**) 11-05-2009, 02:25 PM

I don't think a used garage sale antenna should be considered a valid representative sample of the quality that Dave's company produces.

My .02

zguy1243 · #13 (**permalink**) 11-05-2009, 02:32 PM

Quote:

Originally Posted by burner50

Somebody hit a sore spot?

?

I doubt its a sore spot. When one puts that much time, money and effort into something it becomes personal. I can understand because I am too a business owner. I take what I do very seriously as it seems Dave does too.

DPD1 · #14 (**permalink**) 11-05-2009, 02:34 PM

Quote:

Originally Posted by W9RXR

Dave, I have a suggestion from an innocent bystander...Relax. As a businessman, ranting in public doesn't do you any good.

Of course you're right, but easier said than done.

I just did one myself right now... Same exact materials, 49" long, same exact feed point. The extra 1/4" accounts for the variance in the plastic insulation on the wire batch to batch, because even that changes things...

Inside Tube: Perfect 1.0 between 160.1 and 162.3

Outside Tube: 168.1 and at 160.5 is 3.0

MPSCS · #15 (**permalink**) 11-05-2009, 02:45 PM

Tim:

I can vouch for Dave's character and honesty. I've been doing business with him for a very long time, and I have purchased several of his antennas, as have some of my friends, for general scanning, and Mil-Air. They have always performed well. Customer service was excellent. Along the way I had a few technical questions, which Dave answered promptly, and accurately.

There's nothing wrong with having questions, or concerns about a product, and it's design. But it's best that you take them up directly with Dave in a PM, or at the email address on his site. But to post this in a public forum, for all to see and making comments like the ones below, causes viewers to question your motives:

"Are you guys really getting what your paying for?"
"Maybe if he monitored the feds in the 174MHz area he would have liked it???"

Maybe the antenna you purchased at a garage sale was modified at one time? Or maybe it was a copy that someone like yourself tried to make. DPD also makes custom antennas for some of their customers. Possibly it was one of those.

DPD Productions - Custom Antennas for Commercial & Hobbyist Applications

FLRAILMAN · #16 (**permalink**) 11-05-2009, 03:52 PM

I don't know & personally I couldn't care less, All I care about is the antenna picking up what I want to hear. I own the following antennas from DPD Productions, they all perform as expected & I never had a problem with any of them:

3 outdoor vertical Train-Tennas

1 Indoor Train-Tenna blade

1 outdoor omni Mil-tenna

2 indoor marine blade antennas

I'm not a shill for Dave or DPD Productions, however I tout his products every chance I get if I feel his antennas can solve a dilemma, sometimes they can, sometimes not. I believe if someone makes a quality product that is affordable & he is a member of this group, he & his products absolutely deserve recognition, it's called keeping it in the house. You're a good man Charlie Brown, keep up the good work.

DPD Productions - Antennas & Accessories for the RF Professional & Radio Hobbyist

FLRAILMAN

tonsoffun · #17 (**permalink**) 11-05-2009, 06:40 PM

My antenna system is all DPD antennas, the quality is great, strong and the performance for me is terrific. All antennas are surviving these Canadian winters.
I don't think Dave would let anything leave his hands if it did not meet his specs.
I am all for freedom of speech but, you should have contacted Dave privately, you could have asked those questions directly first before coming to a public forum and calling him out on his products.

How do you know it was not modified before? I will tell you something, give me anything brand spankin new, I will take it totally apart, then I would put it back together without you ever knowing its been apart, trust me on this one.

So if you bought the antenna in a garage sale, you don't know where it has been.

mtindor · #18 (**permalink**) 11-05-2009, 06:58 PM

I own a DPD UHF LP and a DPD Omni-X, and I previously owned a DPD VHF/UHF LP. The craftsmanship of the antennas is outstanding... especially true of the LPs. His antennas (at least the ones that cover into UHF) even have N connectors on them... and most scanner antennas claiming 1000 Mhz performance have SO-239 connectors. DPD antennas perform as advertised.

Dave has always been the consumate professional. There is no reason to doubt the performance of his antennas if you buy them from him. If you get them in a garage sall for $0.10, that's a different story.

Mike

blueangel-eric · #19 (**permalink**) 11-09-2009, 01:00 AM

How do you know it was a traintenna? it doesn't say it on the product.
Like others said it could've been a custom model or something someone else made.

Quote:

Originally Posted by timkilbride

I picked one up at a garage sale, pulled the guts out and its only 48 3/4" long! Should be close to 53". Based on my skills, this thing is cut for 174MHz. The feed point is at 2 1/2", should be closer to almost 4. The "notch" cut is at 16" and only runs for 1/4", should be cut at 17 1/2" and run for 3/4". Are you guys really getting what your paying for?

I have attached some plans if you want to build your own. You can either make it out of 300ohm twin TV lead or 450ohm ladder line. Once made, slide it into a PVC pipe, cap the ends and you have a antenna. I bought 100 feet of 300ohm cable at Radio Shack for $20, 120" of PVC is $1.50, end caps are .50. I built one for myself that is actually tuned to 161MHz, and have been using the left over 300ohm cable making antennas and selling them. The other three pictures are the "guts" of the traintenna.

Tim K.