DPD 118-1000 MHz LP antenna first impressions

[radiopro52]

After using a RadioShack 20-176 for about a year, and upgrading coax and moving the antenna to a higher mast, I decided I may as well go all the way and upgrade the antenna as well. The 20-176 was actually a good antenna. I was listening to ham repeaters over 100 miles away with it, and police stations that were over 60 miles away. I researched several different antennas, including the scantenna, discones, and the DPD antennas. After reading up on DPD's antennas on this site, I decided that the DPD LP was the best bet. It had the most elements and gain, and it was made in America. My first impressions of the LP antenna follow.

Here's a picture of the antenna installed on my mast.

Looking at the above picture, it looks like the antenna is surrounded by trees, but it's not. I just wanted to get a close shot. I'm going to lower the TV antenna that's located below the LP in the future to get it away from the LP. The LP is mounted about 21.5 feet in the air, using 50 feet of LMR-400 coax attached with an adapter to the LP's RG58.

Here's another view from the other side:

I have the LP pointed north east, as that's where most of my desired signals are coming from (Decatur AL, Huntsville AL, ect.). I can tell that the LP is not as omni-directional as the 20-176. However, it does hear in all directions. The LP does hear signals best in the direction it is pointed, and that's where the gain is. For the most part, the things I listen to that do not come from the north east are received the same way with the LP, compared to the 20-176. An exception is a VHF frequency, which is my county EMS. It came in near full strength with the 20-176, but unfortunetly it only has two bars of signal strength using the LP. It was only one bar, but after the corrections I made, it did make it a little better.

Other than that, in VHF the LP performs very well. Local airports come in stronger, and I am hearing things on a VHF search that I have never heard before. Compared to the 20-176, the LP does a little better in the gain area. However, on some VHF freqencies, it does worse.

UHF is where the LP really outpeforms the 20-176. My local city police's UHF system comes in full signal now. And the "channel 2" frequency of the police station, which was always scratchy and weak before, comes in clear now with a few bars. Ham repeaters in UHF also come in much better. A neighboring county's EMS UHF frequency also comes in stronger. I'm very satisfied with the LP in 400 Mhz.

Finally, there's 800 Mhz. After fixing the mistakes, I have now noticed an improvement in 800 Mhz reception with the LP. The Huntsville trunking system's data channel now comes in, instead of fading in and out. In fact, I think it's safe to say that I do notice an increase in performance in 800 MHz now with the LP compared to the 20-176. The signal is still weak, but that's expected in this band.

I'm using the BCT15 which can listen to FM Radio broadcasts. With the LP, all of my local radio stations come in full signal, and even some that are not local come in at full signal.

The LP is very well-built. The materials obviously aren't cheap, and the antenna was very easy to assemble. Dave is a very nice person to talk to and I'm happy to own one of his antennas. I'm going to continue to experiement with the LP and see what other results I get. If you buy the LP, I recommend installing it with a rotor so you can get the gain in all directions.

So, is there a difference after fixing the problems? Yes. Performance in VHF does seem to have gotten better, and performance in 800 Mhz has increased for sure. So, with the attenna now installed correctly, I will say that I am happy with it's performance. Overall, it does perform better than the 20-176 with a few exceptions. But a rotar would probably make the experience even better, and I may put one on in the future. Here's one last picture of the entire mast:

 

[DPD1]

Just a couple observations... Maybe it's an optical illusion, but the small beam looks pretty close. That could possibly distort the field a little. Also... Technically this would make no difference in performance, but it's upside-down. The cable should be on top. The only adverse effect that might have is that water may be more damaging on the cable underneath, as opposed to being above. And the big one... Is the gasket between the boom and the mast? Because I see something dark there on the outside. If the gasket and insulators aren't in the right place, the antenna will make electrical contact with the mast, and basically you've got one giant extra element on your antenna. The coax might need a little slack with less sharp bends, and also make sure the connector isn't being pulled on. Clamp connectors will pull off fairly easily. They need to be supported with ties around the cables.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[radiopro52]

Just a couple observations... Maybe it's an optical illusion, but the small beam looks pretty close. That could possibly distort the field a little. Also... Technically this would make no difference in performance, but it's upside-down. The cable should be on top. The only adverse effect that might have is that water may be more damaging on the cable underneath, as opposed to being above. And the big one... Is the gasket between the boom and the mast? Because I see something dark there on the outside. If the gasket and insulators aren't in the right place, the antenna will make electrical contact with the mast, and basically you've got one giant extra element on your antenna. The coax might need a little slack with less sharp bends, and also make sure the connector isn't being pulled on. Clamp connectors will pull off fairly easily. They need to be supported with ties around the cables.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

The antennas aren't that close together, but they are somewhat close. I will be moving the TV antenna lower.

Upside down? Oops.... I thought the coax would go underneath so it would be hidden from rain and sunlight. I installed the elements as the directions stated, with the coax on top. But I thought that was upside down. Well, I could correct it, but that would have to wait, lol.

If you're reffering to the gasket that's between the boom and the bolts that screw into the mount, I left that the way it was. If that's not what you mean, point it out to me.

 

[mancow]

The boom needs to be electrically isolated from the support arm. It looks like that black plastic thing is on the underside and the support arm is physically touching the antenna boom with nothing in between to isolate them.

 

[radiopro52]

The boom needs to be electrically isolated from the support arm. It looks like that black plastic thing is on the underside and the support arm is physically touching the antenna boom with nothing in between to isolate them.

.......

I see what you both mean now. The gasket needs to go under it where it's touching the boom, not above it where it's visible. Hmm, I must of skipped over that page in the directions.

Well, now that I feel foolish, lol, I'll fix these problems soon and update the impressions. Maybe it'll make it even better.

 

[DPD1]

OK, that might be a performance issue then. Checkout the drawing in the manual. Ideally... Using the top shot as a ref, I'd take the whole thing and spin it like the hand of a clock so the cable is on top. So now it's pointing the other way, but you can re-clamp the mast. Then, hang it under the horizontal mast instead of put it on top. So once it's like that, you would put the stuff together in the order going top to bottom: screw head> plastic insulator> horizontal boom plate> gasket> boom> metal washers> plastic insulator> nut. The metal washers being on the boom side is also important because the tube is weaker and that helps prevent dimpling from the nuts being tightened. Also some loctite on those nuts is a good idea, just to prevent a possible disaster someday.

On your 800, that would probably change with redirection. I know everybody hopes for improvement across the board, but it's give and take. There's really no way to design a high gain antenna that covers as many bands, without going directional. At least not something the average consumer could get anyway. That's just the way nature works. That's why the traditional TV antenna has stayed the same for so long.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[mancow]

Log Periodics are a different animal. The booms are actually part of the electrical circuit. Each element is essentially an active element not just a piece of metal hanging there for signals to "warp" around like a yagi.


Damn.... now all this talk got me so interested in one I went and ordered one just now.

Ahhhh... more money.

 

[radiopro52]

I didn't think the LP would do worse on 800 MHz though. Since it has so many more elements that are all different lengths tuned to all the bands, I really thought I would see a jump in performance on 800 Mhz. I wasn't expecting a big jump, but, you know what I mean. But maybe these corrections will help it.

Good choice, mancow. I'm sure you'll be satisfied with it. Just don't be like me; Make sure you install it correctly :lol:

 

[mancow]

I can see how you could have done that. It would be easy to overlook in the haste of getting it all put together.

I have an Elk brand dual band Log right now and it works incredibly well so I'm anxious to see what this will do. I've been looking at them for a long time. I'm getting ready to put the antennas back up after a bad storm took them down so I figured this would be the perfect time to try one.

Let us know what changes after the adjustments are made.

 

[radiopro52]

I can see how you could have done that. It would be easy to overlook in the haste of getting it all put together.

I have an Elk brand dual band Log right now and it works incredibly well so I'm anxious to see what this will do. I've been looking at them for a long time. I'm getting ready to put the antennas back up after a bad storm took them down so I figured this would be the perfect time to try one.

Let us know what changes after the adjustments are made.

Yeah, I was very eager to put it up and see how it performs. I don't think I was rushing to put it together, but I really just overlooked it. Once I had all the elements on, I was ready to go outside.

I'll correct these mistakes and update the photos. I'll also let you know if there's any change in performance. Thanks to you both for pointing these out to me.

 

[DPD1]

Don't feel bad, you've got plenty of company, believe me. Sometimes I wonder how much stuff is out there not doing as well as it could be. Probably a lot.

The thing about the higher bands like 800 is that they are more susceptible to blocking and also don't bounce as much. So the directional thing starts to take effect a lot more. If you could tune the direction by ear, you might get a good difference in the 800. Just a few degrees could make a difference. Most people do report a bump in 800-900 performance, so I'm thinking there might be room for improvement there. But who knows, the gasket could change things too.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[PHOENIX_SCANNER]

If that antenna is touching the metal of the mast as it appears to be, I believe your whole mast is now the antenna element, or worse yet if you grounded your mast your whole antenna is shorted to ground. The yagi I use for 800 mhz is the same way. I believe you are supposed to mount this antenna on a pvc mast. I used my steel mast for my yagi, but it is a small antenna and wrapping the mast well with electrical tape did the trick in my case.

The 20-176 DOES have 800 mhz elements though, two of them, at slight angles near the base of the main element. It is actually a lot harder to beat a 20-176 than people realize, especially at VHF-HI.

But I have been looking at that LP for a while now. I just have so many things coming from ALL directions I am just not sure I want a directional all band antenna, but this thread tempts me.

 

[radiopro52]

Ok, I've fixed all the problems. Let me know if there are any more

Photos have been updated, and I've revised my first impressions a bit. Just remember that these are my experiences, so your milage may vary.

One question though. Does it mean anything when you're receiving a frequency that the scanner says is a full 5 bars of signal, but it still sounds scratchy like it's much weaker?

 

[af5rn]

One question though. Does it mean anything when you're receiving a frequency that the scanner says is a full 5 bars of signal, but it still sounds scratchy like it's much weaker?

Interesting question. The Fort Worth, Texas public safety trunk system has always done that to me. Not just on every scanner, but on Motorola radios too. It's a weird, hollow, throaty sounding scratchiness that gets better with signal strength, but never totally goes away, even in the middle of town. I haven't figured it out.

 

[DPD1]

Ok, I've fixed all the problems. Let me know if there are any more

Photos have been updated, and I've revised my first impressions a bit. Just remember that these are my experiences, so your milage may vary.

One question though. Does it mean anything when you're receiving a frequency that the scanner says is a full 5 bars of signal, but it still sounds scratchy like it's much weaker?

That could be a problem on their end. Either that or you're getting blending or some kind of interference mixed in. It's hard to say. If it's one of the higher band newer systems, I hear weird stuff like that quite a bit. That's why I hate the new systems. There's nothing like the good old wide-band VHF analog stuff. I really hate to see it all go.

But I'm glad you worked it out. Only other thing I would suggest is getting the cable more up on top of the horizontal piece at some point. That tie will probably wear through the cable eventually. I can't tell, but hopefully you have the larger cable supported under the connector, because if the weight of the cable is on there, I can guarantee it will pull the connector off the cable eventually. Also losing the adapter wouldn't hurt at all. You could possibly get a hair better high band if that was gone. Maybe it's the photo, but looks like your mast might be a little slanted. Keep in mind that thing has a lot more mass than the old antenna, so be careful about keeping the mast in order. Honestly the most challenging thing about these is not the antenna, but the mount. Having to mount them vertically is a giant pain and a big engineering issue. It would be so easy to mount horizontally like the hams do, but that won't work for scanning.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[radiopro52]

That could be a problem on their end. Either that or you're getting blending or some kind of interference mixed in. It's hard to say. If it's one of the higher band newer systems, I hear weird stuff like that quite a bit. That's why I hate the new systems. There's nothing like the good old wide-band VHF analog stuff. I really hate to see it all go.

But I'm glad you worked it out. Only other thing I would suggest is getting the cable more up on top of the horizontal piece at some point. That tie will probably wear through the cable eventually. I can't tell, but hopefully you have the larger cable supported under the connector, because if the weight of the cable is on there, I can guarantee it will pull the connector off the cable eventually. Also losing the adapter wouldn't hurt at all. You could possibly get a hair better high band if that was gone. Maybe it's the photo, but looks like your mast might be a little slanted. Keep in mind that thing has a lot more mass than the old antenna, so be careful about keeping the mast in order. Honestly the most challenging thing about these is not the antenna, but the mount. Having to mount them vertically is a giant pain and a big engineering issue. It would be so easy to mount horizontally like the hams do, but that won't work for scanning.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

I first noticed it on a very low ham frequency, I think 29 Mhz. It was very weak, yet it said it was full signal. And when it got worse so that it was barely understandable, it still said it was three bars.

I have a couple of stand-offs that I'm using. I put a little bit of slack on the coax so the full weight of the LMR400 isn't pulling on the connectors. I guess it is a little, but not enough to pull it out.

The adapter is required because the end of the LMR has a PL-259 connector on it so that it would connect directly to the 20-176. The adapter is probably hurting some, especially when you're trying to pull in weak signals. Plus using the adapter probably cancels out the advantages of an N connector, since the signal is still going through the PL-259. But I can't do anything about that at this time. Connectors are hard to install on LMR coax, I hear, and I don't feel like getting all new coax just to get another connector.

Some bending and bouncing is probably going on. I notice on my local police, sometimes the signal is full strength. And then on the next transmission, it may drop to a single bar and then fluctuate up and down until the next transmission. It doesn't do that on all the frequencies though. I seem to be getting that mainly in UHF.

 

[af5rn]

I hate to state the obvious, but are you sure it is not the units transmitting into the repeater that are weak and scratchy, and not the repeater itself? That would result in a full signal to your scanner, but a scratchy reception.

 

[radiopro52]

I'm pretty sure it was the repeater, since it totally dropped out a couple of times. But when it did that, it still said it was three bars strong. But it was also very distant. Looking up the frequency, 29.620, on this website, the nearest repeater to here on that frequency is in Fort Walton Beach, FL, almost 300 miles away.

 

[af5rn]

Ah! Well if it's skip, then yeah, weird things will always happen, lol. All sorts of strange sounds and unpredictable on-again/off-again propagation.

 

[DPD1]

The adapter is required because the end of the LMR has a PL-259 connector on it so that it would connect directly to the 20-176. The adapter is probably hurting some, especially when you're trying to pull in weak signals. Plus using the adapter probably cancels out the advantages of an N connector, since the signal is still going through the PL-259. But I can't do anything about that at this time. Connectors are hard to install on LMR coax, I hear, and I don't feel like getting all new coax just to get another connector.

It's the kind of thing that just takes a little practice, but it's not hard. I know there's a lot of people that have the same issues with cable. I've thought for a long time on how I could help, but I haven't come up with anything. The problem is that, until you start buying thousands of feet of cable, the cable makers will barely give you any price break at all. Unless you buy huge amounts, they prefer you at least go through a distributor. Lots of times I can't even do that. So then it's like I'm almost paying as much as everybody else. It's not like the old days where anybody with a business gets a wholesale price. It's very similar with connectors as well. So even on the expensive stuff, I'd be lucky to get .10 profit a foot. On top of that, I know that no matter what cable I carried, people would always want something else. So now you're looking at having thousands of dollars of cable laying around, just so you can help the occasional person who needs something. It's just tough spending that kind of money these days to inventory something that has so low a profit margin. You'll see the same reflected in what few electronic supply places are left. Most don't stock half of what they did just 10 years ago. Even in a city as big as L.A., you're hard pressed just to find many connectors. The internet is great, but it's also had a very negative effect in that regard.

Dave
http://www.dpdproductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist