1) The factory harness is typical DB construction with lengths of coax that are Not RG11 and connected using their molded "Y" boots. I made a divider once for 432Mhz out of RG-11 with N conn's and used an N Tee connector with jacks on all three ends which worked just fine for me. I used a return loss bridge to determine the velocity factor of the cable and get the lengths cut correctly.
2) ours is very close spaced to the tower leg so we have all the elements in line facing out from the leg. So I can't help you with other combinations of element locations for a DB228. Check the files section of repeater builders and you will find the DB224 sheets that show the patterns for various element arrangements. 3) I have one other DB224 Instl on top of a building for a while is was mounted all in line and then we changed it to the omni arrangement with each element 90 deg from the previous one. We couldn't tell any practical difference in performance between the two configurations. 4) I looked at some photographs that were taken of the Installation. Yes the lower elements are upside down but I don't remember what was done for drainage. I think they had holes on both top and bottom of the loops. I can't tell from the pics. 5) yes our element spacing varied as well. We readjusted to even the spacing out. This spacing variation was discussed about a year or two back on the reflector. you may want to search the archives for more info. 6) Our DB228 instruction sheets and DB224 sheets included no dimensions what we got with our DB228 is available in the files section of Repeater builders web site. There was a lot of discussion on various dimensions for DB224 antennas a year or two back again you may want to check the archive. Pics of the installation I am talking about can be seen at www.warc1.org John Lock kf0m at arrl.net > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] Behalf Of s3hampton > Sent: Sunday, July 29, 2007 6:19 PM > To: [email protected] > Subject: [Repeater-Builder] Two DB224's to make up a DB228 > > > Good day, John (KF0M) and others; > > I was away all last week, and part of the previous, so I was > unable to give you a PROPER reply to your comments. Others had > comments to add to my situation, but none really had as good of a > reference as you! > > From your data on my "assembly" of two DB224 antennas as a DB228 > array, I will make the phasing harness up with a 1/4 and a 3/4 wave > (after the velocity factor computation of my RG-11 coax). > > I have a few other related questions, if you would please allow: > > > MY QUESTIONS: > 1. Is the FACTORY-MADE harness made up as with the RG-11 type coax > cables MOLDED onto the coax cables? -Or, are the cable "legs" simply > made up, then attached to a coax-TEE? (I want to make my own harness, > you see. It is my plan to solder the RG-11 coax directly to the > required type N connectors.)) > > 2. It is my desire to have the top-most DB224 act as a bi-directional > antenna. As such (with no real info), I have arranged the top-most > two elements so that they are directly in line with each other. The > lower two elements are also directly in line with each other, but they > are are on the opposite side of the mast. (Elements 1 and 2 face > North; Elements 3 and 4 face South.) > Or, should elements numbered 1 and 3 be facing North (as an > example) and elements number 2 and 4 be facing South? > -I have NOT put the new DB224 up, yet. > > 3. I have no concrete plans for the lower DB224; It could remain as a > 360 degree coverage, or I could set it up with elements 1 and 4 at > North and South, respectively; Elements 2 and 3 would then "span" one > side of the mast, soas to offer more of a carderoid (sp) pattern. -In > this case, the elements would face 0, 60, 120 and 180 degrees. (Your > suggestion, please?) > > 4. It is my ASSUMPTION that the top-most DB224 be "right side up," > and the lower DB224 be mounted upside-down. Is this correct? > If this is the case, the lower DB224's elements will be "hot side > down," which is opposite from how the top-mounted DB224 has the > elements arranged. > If I mount the lower DB224 upside-down, will this retain water, > which will freeze and damage the antenna? (Yes, the 1/4 and 3/4 > wavelength phasing harness will insure a proper phase, so I will > actually realize GAIN.) > > 5. The SPACING of the elements is far from "even; In my case, as well > as other reported element arrangements, I see from 60 to just over 70 > inches of center-of-element to the next like point. I had fully > expected to see an exact measurement! I have a Cushcraft 4-bay > antenna, whose setup has all four elements at a fixed, and EQUAL > number of inches, +/- 1/8 inch!! (I cannot locate the instruction > manual for my HyGain 4-bay J-Poles, but I am assuming that the > element-to-element spacing is the same (equal), and exact; These > examples are so very much different from what the DB224 units seem to > all be set up as. So: What is correct??? Is there some hidden magic > from the phasing harness and the seemingly inexact element placement > that actually allows a focus of the RF energy where it is needed? > -Or, is this really an important factor?? > > 6. In looking at the pictures and diagrams of the DB228 > documentation, I see that the images (as an example) show that the > top-most DB224's four elements are .75 inches > center-line-to-center-line. I see the exact same for the four > elements on the lower DB224. But, the centerline spacing of the > fourth element (lowest one) to the now-upper element of the lower > DB224 is somewhat more than 1.2 inches. (?????) Is this actually > correct? -Or are the pictures and the drawings simply made up by > someone other than an engineer? Here again, I had assumed that the > element spacing "should be" even, and exactly the same! > > Thank you in advance for your time and effort!! > > 73! > > -Mike- > K0JTA > > > > > > > > Yahoo! Groups Links > > > >
