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Message: [QUOTE="JER, post: 32694, member: 4529"]What makes a good DTV antenna?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 <a href="http://www.johnross.com">John Ross and Associates - Electrical Engineering</a> 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.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 sell2. 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.<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" /> Now that we have the important stuff out of the way...4. Impedance bandwidth - we targeted VSWR less than 3:1 across the whole band and achieved much better than that in most of it5. 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,JohnPS - 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...[/QUOTE]

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