Antenna Gain - Is it the ultimate measure of a better antenna?

JER

DTVUSA Member
#21
Big Antennas versus Antenna Farm

Agreed! Let's steer the thread back to its original intent on discussing relative merits of different factors that are important for reception.

One of the things that strikes me as an antenna engineer is the fact that so many of the designs on the market are still the large VHF/UHF combo antennas. While they are a tried and true designs they only work well for people who are in markets where all the stations are in one direction or for people willing to use a rotator. The truth of course is that most people live in markets where they have to contend with transmitters from multiple directions and multiple bands. The days of using a rotator to watch TV on a single channel pretty much died once we invented the remote control. Most homes now also have several TVs so it seems to me that a small antenna farm makes more sense than a single "big gun" antenna.

The low VHF band is also problematic. Physics makes it hard to design good small antennas and now the market for Low VHF is so small that it would be difficult for to recoup any substantial investment that one might make developing new antennas for that band.

Personally, I think the FCC made a mistake by not forcing all the DTV stations into one big UHF band so that we could accommodate the consumers preference for small TV antennas and in the future mobile TV. They could have easily reallocated the VHF bands to other services that can live with large antennas and that can make better use of the VHF propagation characteristics. What's done is done of course so now we must try to solve the problems...

We are hearing that much of the post transition VHF reception problems have been indoors and related to electronically generated noise (TV's, computers, etc.). The VHF noise in and around most homes is now apparently much higher than the assumptions used in planning the TV coverage areas. So, while signal strengths are still good and in line with predictions, noise margins are too small or even negative indoors. This is causing lots of grief for viewers and VHF station owners alike.

Apparently the problem isn't as bad outdoors away from buildings and electronics. In many cases amplified antennas have been found to worsen the problems as the noise/interference is strong and amplifiers only make it worse. High VHF is apparently strongly affected by harmonics and intermod from strong FM stations so removing amps and installing FM traps apparently helps in some cases.

For FoxTV: I would encourage you to take a look at our C5 VHF antenna if you have time. I think it will suit your needs for a compact high VHF solution. You'll find specs and computed data on the antennas direct website!

Cheers!
 
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EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#22
Couple of things, the ClearStream Antennas are wide beamwidth antennas....much wider than the 4 Bay Bowties that Piggie was talking about in the OP. I have tested both the ClearStream2 and the ClearStream 1 Convertible and both are great antennas on UHF.

Furthermore the Bowtie Antennas are Colinear Broadside Arrays, which are basically stacked Full Wave Dipoles....which have nulls off the ends.....which means serious side rejection. Also they phase cancel each other out from the top and bottom so are also good at rejecting overhead and below(ignition used to be the big one) noise.

There rear rejection can be excellent at the 20 db average level on UHF....which is equivalent to yagis corner reflector or otherwise.


My 2 cents.
 
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Piggie

Super Moderator
#23
Hi,

First off, let me say right up front that I'm the inventor of the Clearstream antennas. I work as a consultant to Antennas Direct as well as many other companies and agencies. If you're interested you can see my website at John Ross and Associates - Electrical Engineering so that you know what I'm all about.

Secondly, I want to say thanks to Fox TV for sharing his field testing experience with the Clearstream antennas. Antennas Direct and I appreciate the feed back and find it gratifying to see that our products being used and appreciated in your application.

Lastly, I'd like to discuss briefly how we came up with the Clearstream tapered loop / reflector idea and what factors tended to make it a success.

The Clearstream effort started out internally as an effort to create a very compact antenna to be integrated with a DTV converter box. We recognized that the antenna was key to such a product so we were focused on finding the most efficient, highest gain, directional antenna that we could fit in the smallest practical space and which would perform over the post 2009 UHF DTV band.

We looked at a lot of options but one option that looked interesting was the full-wave loop in front of a reflector. This geometry has been known for at least 5 decades to produce 9 dBi if you could feed it properly. Best of all the loop could be placed close to the reflector and still retain the forward gain. Right away we knew a thick loop would be required to cover the bands and we iterated solvers (NEC and X-FDTD) to do trade offs on loop size, thickness, reflector spacing and reflector size. Eventually we found one that worked good and covered the band but it still was too big to fit our package requirements.

My background is in UWB radar so one day I stumbled onto an IEEE paper where the authors were using tapered circular slots for pulse radiation so I tried tapering our loops and next thing you know we had better bandwidth and things really started to take shape. In backyard field tests our first single loop (C1) prototypes were performing as well as the double bowtie (DB2) but took up only 1/2 the volume so we began thinking of the antenna as something more than just part of a converter box part and went off and did the double (C2), quad (C4), and high VHF (C5). Other iterations are sure to follow.
I have always like loop antennas, and thought the idea behind the tapered loop was an interesting twist on the tapered dipole antenna, we used to make for more bandwidth on 80 and 40 meters. Two idea from the past incorporated into a new design. I always like that idea.

It's not the antenna, your design or the engineering that causes me trouble. It is the marketing and even you stated above:

The Clearstream effort started out internally as an effort to create a very compact antenna to be integrated with a DTV converter box. We recognized that the antenna was key to such a product so we were focused on finding the most efficient, highest gain, directional antenna that we could fit in the smallest practical space and which would perform over the post 2009 UHF DTV band.
We can call it semantics, but to me the C1,2,4 are UHF antennas, and only happen to have some response on VHF. While they and other antennas have rear screens that resonant at VHF and will provide a lot of urban and suburban viewers with enough VHF response, I personally can't call them VHF antennas.

In looking back on this effort several things stand out insofar as what makes a good DTV antenna for the MASSES:

1. Size - yes, size matters, the smaller the better or it won't sell

2. Size - the smaller it is, the more likely that it will go up on the roof. This dramatically improves reception almost every time!

3. Size - often referred to as Wife Acceptance Factor (WAF). It has to look good (aesthetics) or not be seen (better aesthetics). Ultimately it all boils down to size. See 1 & 2 above.

1. If size mattered that much why do the other companies sell their larger antennas. I also say size matters, when it comes to VHF where the elements are full sized dipoles. Electrically shortened antennas never have the gain of a full sized elements.

Size is a perception in micro electronics that smaller must be better. Even with your innovative design of a loop and tapered elements in one, it doesn't change the laws of physics for reception.

2. True, getting on the roof, outside the indoor or attic antenna is always better for reception. Saying that improves our antenna is simply marketing. If a person needs deep fringe reception on VHF and fails on your antenna, they might give up and think the DTV transition was a failure as they bought the antenna as marked for the DTV Transition but it won't pick up VHF.

3. Having been around during the period antennas became suddenly ugly, the source was not the wife but the cable TV companies. They mounted campaigns to local governments about ugly TV antennas. They also gave kickbacks to developers that put in their deed antenna restrictions for every person that signed up for cable. As a ham I know these conflicts well, fighting to be able to put up my ham antennas, where and who started the problem for me.

It was their marketing that put in the heads of wives and a lot of husbands that antenna were ugly, lowered property values. It is a right to be able to put up an antenna on private property to receive the public airwaves.

There are people like me that think a long boom yagi is a work of art, a sculpture of aluminum.

;) Now that we have the important stuff out of the way...[/qoute]

I would call the first three marketing influences not the important stuff.

Below is the important stuff.

4. Impedance bandwidth - we targeted VSWR less than 3:1 across the whole band and achieved much better than that in most of it

5. Forward gain - We took what we could get, but the gain we got (approx 8 dBi for C1) was very flat versus frequency across the band.

6. 1/2 power Beam width (horizontal plane) - C1 has about 70 degree beam width on all UHF channels. Most antennas have beam width that decreases with frequency so the clearstreams should be easier to point.

Note - I personally think that sometimes people get antennas that have too much gain and beams too narrow to be effective in their markets. Channel surfing - even with a single TV - is so essential that the days of a rotator are pretty much done. I believe that a moderate beamwidth - say 50 to 90 90 degrees - may be a better for most folks.

7. Front-to-back - We took what we could get. The C1 has F/B of 12 to about 18 dB or so depending on channel. Higher channels were better.

8. Side lobes - Clearstream side lobes were generally much lower than F/B since the peak lobe is usually the rear lobe.

9. Forgiving structure - this is important for manufacturing and consumer installed antennas. We can have the best highly tuned antennas in the world but if we can't build them on an assembly line and have a consumer install them without needing an Agilent vector network analyzer then we've failed. The Clearstreams seem to be very forgiving to placement and since they are small we can ship them with simple (in some cases 1 bolt) assembly.

10. Pulse fidelity - This is speculation on my part, but Clearstreams are wideband structures that that can radiate / receive band limited pulses without a lot of distortion. While log-periodic dipole arrays are also wideband they do NOT do well when radiating / receiving pulses due to what is known as phase dispersion. I have a hunch that this may be one of the reasons that the Clearstreams sometimes do better than much larger antennas on digital signals, but have yet to prove it all out in a practical test.

Let me repeat, the above antenna considerations are for the masses, not the deep fringe enthusiast who has no problem with 80 ft towers, 10 ft booms and rotators.

Sorry for the long first post. I hope you all find the information useful.

Best Wishes,

John

PS - I too hate the rating of antennas with mileage. I'd much prefer to see all the gain charts and VSWR graphs on the box but the average Joe will have no idea how to interpret that so I fear we're stuck with miles...
You should put on the boxes, will work ok if you live near a VHF tower. Admitting here that they are not for the deep fringe people or 80 foot tower people has not helped those I helped when they bought the wrong antenna thinking it was a deep fringe antenna.

If the antennas were marketed more for what they really do I would less of a problem with them.
 

Piggie

Super Moderator
#24
During the Antennas Now Road Tour, company president, Richard Schneider, gave away untold thousands of antennas and helped countless numbers of people learn how to save money in a recession by switching from cable or satellite to free OTA DTV. He criss-crossed the country in his bus evangelizing antennas and OTA DTV to just about anyone who would listen. He was often up in the middle of the night giving TV interviews for the morning news casts and then spent the day at a local TV station or Best Buy parking lot helping average Joe's and Joanna's figure out how to solve their reception problems. That doesn't sound like a "snake oil" tour to me?

Antennas Direct, like most US companies these days uses off shore manufacturing. While I think most of us would prefer domestic manufacturing we all know the realities of that situation and its unlikely to change anytime soon. I recommend raising that issue with your elected representatives rather than here.

Thanks again for reading!
Giving away antennas is advertising.

I will continue to support companies that manufacturer in the US.

The reality of the situation is we have moved so many manufacturing jobs off shore in the search for cheaper labor and with government incentives to do so, it's a wonder anything is made in the US.

However this is going to lead to a jobless recovery from the recession and be more just the way it is in the US. We ran for years without the jobs on credit that has now dried up based on inflated home values to a large part. An economic system can't run forever on just increased real estate and new homes, it sooner or later hits a limit that we saw happen.

If find here an excellent place to discuss the merits of the situation. It's gone beyond politics into the wallets of Americans that have been told now for 20 years, it's just the way it is now, sorry.

I am not advocating nationalism, as that is also bad economic policy but just accepting the average worker has less to money and will have even less money in the future because it's just the way it is , is unacceptable to me. It's time to start talking about this every where.

Again, I love the concept of a better UHF antenna in the C1,2,4. I have deep disdain though to take something to be more than it is, things are the way they are, it's ok, and any spin to market a product is just ok anymore, as everyone else does it.
 
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Piggie

Super Moderator
#25
Couple of things, the ClearStream Antennas are wide beamwidth antennas....much wider than the 4 Bay Bowties that Piggie was talking about in the OP. I have tested both the ClearStream2 and the ClearStream 1 Convertible and both are great antennas on UHF.

Furthermore the Bowtie Antennas are Colinear Broadside Arrays, which are basically stacked Full Wave Dipoles....which have nulls off the ends.....which means serious side rejection. Also they phase cancel each other out from the top and bottom so are also good at rejecting overhead and below(ignition used to be the big one) noise.

There rear rejection can be excellent at the 20 db average level on UHF....which is equivalent to yagis corner reflector or otherwise.


My 2 cents.
stacked full wave dipoles?

I believe I said previously I did like the idea of collinear antennas with elements stacked not just vertically but also horizontally to improve front to side rejection.
 

JER

DTVUSA Member
#26
Dead horse

It's not the antenna, your design or the engineering that causes me trouble. It is the marketing and even you stated above:
...

We can call it semantics, but to me the C1,2,4 are UHF antennas, and only happen to have some response on VHF. While they and other antennas have rear screens that resonant at VHF and will provide a lot of urban and suburban viewers with enough VHF response, I personally can't call them VHF antennas.

...

You should put on the boxes, will work ok if you live near a VHF tower. Admitting here that they are not for the deep fringe people or 80 foot tower people has not helped those I helped when they bought the wrong antenna thinking it was a deep fringe antenna.

If the antennas were marketed more for what they really do I would less of a problem with them.

Errors were made early on in the Clearstream marketing materials. To the best of my knowledge those issues have long since been corrected. If you check the Antennas Direct website I believe you will find that the Clearstream models are now accurately characterized. All companies make mistakes. The ones that want to continue correct them.

The horse you're beating is now dead. Antennas Direct is working to put into place systematic measures to ensure technical accuracy of its marketing materials so that it stays that way.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#27
stacked full wave dipoles? --- Piggie

Yes 8 + 8 = 16

16 equals a full wave at Ch. 58. Add in a 1.5 inch gap and it equals a full wave at 48.

The fans are basically dipoles.
 

JER

DTVUSA Member
#28
Advertising and Off-shore manufacturing

Giving away antennas is advertising.

I will continue to support companies that manufacturer in the US.

The reality of the situation is we have moved so many manufacturing jobs off shore in the search for cheaper labor and with government incentives to do so, it's a wonder anything is made in the US.

However this is going to lead to a jobless recovery from the recession and be more just the way it is in the US. We ran for years without the jobs on credit that has now dried up based on inflated home values to a large part. An economic system can't run forever on just increased real estate and new homes, it sooner or later hits a limit that we saw happen.

If find here an excellent place to discuss the merits of the situation. It's gone beyond politics into the wallets of Americans that have been told now for 20 years, it's just the way it is now, sorry.

I am not advocating nationalism, as that is also bad economic policy but just accepting the average worker has less to money and will have even less money in the future because it's just the way it is , is unacceptable to me. It's time to start talking about this every where.

Again, I love the concept of a better UHF antenna in the C1,2,4. I have deep disdain though to take something to be more than it is, things are the way they are, it's ok, and any spin to market a product is just ok anymore, as everyone else does it.
Yes, giving away antennas is advertising, but its good advertising that helped a lot of people save some money in a recession.

Personally, I wish we had domestic manufacturing capability. While we continue to evaluate such options the odds are stacked against us. We are a small company that is competing against some much larger players. We are also generally at the mercy of big box retail that drives prices to the point where the only way anyone can make a profit is by manufacturing overseas. Consider that big box wants a buy price of 70% off list or more and you'll rapidly see how hard it would be to do manufacturing here and make a profit. I wish it weren't this way but like you we are powerless to change it. Again I think this topic deserves its own thread somewhere else.
 

JER

DTVUSA Member
#29
1. If size mattered that much why do the other companies sell their larger antennas. I also say size matters, when it comes to VHF where the elements are full sized dipoles. Electrically shortened antennas never have the gain of a full sized elements.

Size is a perception in micro electronics that smaller must be better. Even with your innovative design of a loop and tapered elements in one, it doesn't change the laws of physics for reception.

2. True, getting on the roof, outside the indoor or attic antenna is always better for reception. Saying that improves our antenna is simply marketing. If a person needs deep fringe reception on VHF and fails on your antenna, they might give up and think the DTV transition was a failure as they bought the antenna as marked for the DTV Transition but it won't pick up VHF.

3. Having been around during the period antennas became suddenly ugly, the source was not the wife but the cable TV companies. They mounted campaigns to local governments about ugly TV antennas. They also gave kickbacks to developers that put in their deed antenna restrictions for every person that signed up for cable. As a ham I know these conflicts well, fighting to be able to put up my ham antennas, where and who started the problem for me.

It was their marketing that put in the heads of wives and a lot of husbands that antenna were ugly, lowered property values. It is a right to be able to put up an antenna on private property to receive the public airwaves.

There are people like me that think a long boom yagi is a work of art, a sculpture of aluminum.
I'm also a ham and have been playing with antennas since I was 12. Like you, I can appreciate antennas large and small. I also live in a place with some of the most amazing landscapes on the planet and to be honest, I prefer to see the beauty of nature rather than my neighbors TV antenna. In this respect I can't say that HOA rules and deed restrictions on certain types of antennas are necessarily a bad thing.

On the other hand I don't think it has to be a zero sum game. If we are innovative and resourceful we should be able to develop antennas that enable us to have TV or pursue radio hobbies but that preserve our views and property values. We simply have to work harder to make our antennas perform better and fit within the constraints of modern living. To that end, size does matter!

Size matters because most consumers nowadays have become accustomed to using a 3 oz cell phone to talk, text, e-mail or surf the web anywhere anytime. They can't comprehend why they need an antenna with a 10 ft boom to get TV? If it has to be that big most of them will just punt and get cable or a small satellite dish.

Courtesy of the computers and iPods consumers come to expect more, better, faster, smaller, cheaper, cooler all the time. No consumer electronics company can afford to ignore this.

Size matters because high shipping costs drive down profits. My local Radio Shack dealer has told me that he cannot carry or sell large antennas because of high shipping costs.

Size matters because box box retail generally won't accept an item unless it generates a certain minimum amount of revenue/profit per INCH of shelf space. That's why you don't see big VHF/UHF combo antennas at your local store.

Size matters because most people buying newer homes in this country are faced with CCNR's that prohibit antennas. Despite laws to the contrary most people don't want to take the risk of putting up a big antenna and getting into a fight with neighbors or the HOA. They will however take a chance and put up something small or covert if they get the chance.

For the most part, the world I live in is not one where I get to make the "biggest baddest" antenna because as I have indicated above with few exceptions those don't sell or make a profit. Instead, I'm working to develop products that pack the best performance, into the smallest, coolest or covert form. To do this we're using our wits, going back and re-examining the old assumptions, and pushing the limits of physics with computers and software that would have been inconceivable just 20 years ago. The Clearstream antennas resulted from exactly this kind of process. While you are right that the physics of reception hasn't changed, our understanding of it and our ability to exploit it has changed courtesy of the computer and software innovations. As an example, consider that we're now using GPU's with Teraflop throughput to run our antenna simulations. This gives us advantages that previous generations of really smart engineers didn't have and allows us to continue to innovate in what is generally regarded as a mature field of study. Again, its all about "more, better, faster, smaller, cheaper, cooler" if we want to be competitive in the market.
 
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EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#30
JER, I really like the Clearstream series.

My biggest gripe (besides the VHF High nonsense) is that the coax attachment point is difficult...limiting cable choices. Some F connector heads wont fit in there. RG59 which is more flexible works better as well.

The seem in the 2 plasctic coverings also might be problematic for outdoor installs, trapping water in the interior, you might think about a drain hole at the bottom.
 
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JER

DTVUSA Member
#31
We're in the process of reworking the base of the Clearstream base now to make it easier to attach the coax. It shouldn't be too long before they are shipping the improved version.

I believe on the seam you refer to is ultrasonically welded so it should be well sealed. The tooling for the plastic molds is expensive to develop and making changes can be risky. I'll check again with the mechanical & manufacturing guys about the sealing and see if they think a drain hole is necessary. Waterproofing enclosures can be tricky and I'm not the expert there. Apparently they need to breath somehow to deal with pressure changes. I'll note that the original idea was to make the Clearstream loops out of thick AL stock so that it would be super solid and impervious to damage but the price of AL is so high we had to switch and do the thin element with the plastic enclosure. In the end, I think the plastic is very strong and perhaps a better use of materials.

We always appreciate constructive suggestions. Thanks!

We also appreciate field reports on our products. Its very helpful for us to know how and where people are using our products and what kind of results they are getting.

As I said we are a small company so for efficiency we use state of the art computer simulators and lab testing in the development process and then follow up with some limited field testing to ensure that what we see in the computer and lab are being realized in the field. The computer sims and lab measurements usually, but not always, show good correlation with performance in the field. We don't however have time or budget to do the kinds of extensive testing that Fox TV is doing as he evaluates his coverage area so having that kind of feed back from experienced and knowledgeable individuals is quite valuable to us.

Thanks again!
 

JER

DTVUSA Member
#33
We're still contemplating a "professional" series with the raw thick AL stock. They would be targeted at commercial type installations where they are mounted on big towers and its expensive to have someone climb a tower to replace an antenna. They would have a premium price though due to materials and short run labor costs.
 

JER

DTVUSA Member
#35
They have improved the sealing process since the first versions began rolling off the line. The latest samples I have seem to be very robust. If you bought the antenna from the website you can probably call customer service and get a replacement. They have a fairly liberal return policy.
 

jwalter

DTVUSA Jr. Member
#36
We can call it semantics, but to me the C1,2,4 are UHF antennas, and only happen to have some response on VHF. While they and other antennas have rear screens that resonant at VHF and will provide a lot of urban and suburban viewers with enough VHF response, I personally can't call them VHF antennas.
For what it’s worth, I get high VHF with a ClearStream 2, I have been impressed with the results. I live about 17 miles from the PBS Ch 11 transmitter in Topeka and maintain about an 80% signal level. (In addition I can also receive the Kansas City UHF transmitters reliably at 35 - 37 miles). I bought one for my dad who’s a little closer and he’s had similar results. I know that’s not exactly deep fringe, but for many people a C2 would probably be fine for upper VHF.

Does that make it a combination antenna? I don’t know, but as an all around antenna, it’s still better than the bowtie designs I have tried.

Mine is mounted outside and I’m slightly above the average terrain so as always, your mileage may vary.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#37
Ive picked up Ch. 7 at 45 miles away with the ClearStream 1 and a CM 7777 amplifier...however it wasnt reliable in bad weather and wind...but on clear still day, even with full summer leaves, it did the trick. Which was pretty impressive. However, Im not calling it a VHF antenna.
 

JER

DTVUSA Member
#38
I'm glad you brought up the bad weather issue.

I used to live in downtown Salt Lake City where all the transmitters are located on a ridge some 5000 ft above the city. It was amazing to me how, even with the very strong signal levels we had there, that digital reception would be affected by weather - especially high wind conditions.

I'm not a receiver expert but it seems reasonable that the problem may not be an antenna issue so much as it is a result of dynamic multi-path signal conditions (caused by swaying tree branches?) changing faster than the receiver multi-path canceling circuits can keep up. I recall one evening when we were having a really severe wind event (no rain actually) that I couldn't receive any channel reliably.

Any thoughts on that idea? Is this purely a receiver issue?

Has anyone tested various receivers under such conditions to see how they perform?

Is there a specification on a receiver or chipset that indicates how well it would cope with such conditions?

Is there something that could be done on the antenna (short of a "laser beam" pattern) that could help?

How well will mobile DTV will work if/when that technology is rolled out?
 

Piggie

Super Moderator
#39
I tried an Insignia, DTVPal Plus, Toshiba TV, Ölevia TV. Not a bit of difference.

I had the problem constantly on ch 31 and ch 36 my two strongest signals with a CM4221A. I replaced it with a Radio Shack U-75R and bingo problem solved. It has less gain and dropped my quality meter about 5 points on all UHF channels, but it is steady as a rock on windy days, dry or wet leaves.

I changed it before the analog cut off and it was clearly much better on wind leaf driven multipath.

The U-75R has a 47 degree beam width, so it's not a long boom, but had the front to side to solve wind leaf branch driven multipath.

There is quite a bit of information on this forum if you look about Mobile DTV.
 

Piggie

Super Moderator
#40
Errors were made early on in the Clearstream marketing materials. To the best of my knowledge those issues have long since been corrected. If you check the Antennas Direct website I believe you will find that the Clearstream models are now accurately characterized. All companies make mistakes. The ones that want to continue correct them.

The horse you're beating is now dead. Antennas Direct is working to put into place systematic measures to ensure technical accuracy of its marketing materials so that it stays that way.
I would have to see the new boxes. But it's obvious to me you came into this thread to add more Google fodder for your company. It's a sneaky way to advertise while promoting your antenna sales.

I must compliment you on changing a thread where I said I was not a fan of your antenna into a promotion thread for them. Like I said, your company is very good at marketing.

I believe my work here is done.

So you, and several others here between constantly stating things, political views that never end it has worked.

You can have this place all to your own.

Call it the antenna sellers forum.

See everyone here later.
 
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