: Antennas Direct DB4 Hardware Hacks
2010-10-28, 10:45 PM
The new DB4 could be a winner. I own the old DB4, which worked very well right out of the box.
The stock DB4 needed a bit more oomph though for my deepest fringe channels, so I converted it into an M4 (I call it DBM4), by adding large curved reflector, increasing the whiskers to 8" long, and then sweeping the whiskers forward 2". It works extremely well, slightly outperforming my 91XG on 1-2 Edge stations from 114 miles away.
I also removed the DB4 stock balun and replaced it with my best performing balun (made in China indoor model).
The "Regal T-75" indoor baluns also work great with the DB4, and allowed for "some" reception of very weak VHF-Hi channels. Both of these indoor baluns did outperform the stock DB4 balun for my weakest channels (1-2 edge and -2db to -8db NM according to TVFools)
I also tried the usual suspects, i.e highly rated Channel Master and Winegard baluns, but none of them worked as well as these indoor models.
Antenna Direct should be applauded for their approach to improving antenna designs, they make very good products, and their customer service is 2nd to none. They have always gone the extra mile when I phoned for replacement parts.
For the record, I have no affiliation with AD, but credit should be given when due.
Has the DB4 ever been modeled here...?
or even the DB8...
HDTVPrimer posted the graph but most models are missing
They appear brutal before channel #20
2011-12-06, 02:49 PM
I just have Nists DB2a models.
2011-12-11, 05:47 PM
Dated 5Oct2008, mclapp posted a 4nec2 file for the (old) Antennas Direct DB-4:
On 9Feb2009, d510d180 posted a parameterized 4nec2 file for the (old) DB-4 in the
"How to build a UHF Antenna" thread on that forum that shall remain nameless:
Awhile back I was curious re Hi-VHF (only) performance and analyzed mclapp's DB4_300ohm.nec file,
which required adding and adjusting Rsrc for AGT=1.0. I just finished adding UHF analysis & uploaded:
A-D DB4 has serious frequency roll-off on the lower UHF freqs as well as a high SWR on low-mid freqs.
Hi-VHF SWR is Excessive, with more Gain towards the REAR. These are all due to it being TOO SMALL:
Whisker Length=6.17-in, Tine Separation=1.2-in, Feedline Separation=1.8-in, Hop=1.0-in.
BowInner-Inner=7.85-in, BowInner-Outer=7.9-in, Two Reflectors: 12.7"x18.9", Sep=4-in.
2011-12-12, 01:11 PM
Actually, the roll-off and high VSWR (at the low-end of UHF) on the old DB4 was due to something in the phasing lines as I recall our design engineer describing. I didn't catch all the details.
He fixed that issue with the new designs for the new 4-Bays.
Here in Montreal, because the new models of 4-bays, from any manufacturer, are all back order (not available), the retailers are trying to push out the old DB-4s they managed to get in stock, by the thousands. They claim they are quote "very good antenna, on par with the other 4-bays". :eek: ....so please beware.
Unbelieveable widespread ignorance and dishonesty in this industry (yes, I know im generalizing !)
thank you for those models.
2011-12-12, 05:36 PM
The major limiting factor of the old DB4 for lower and Mid UHF versus other "commercially" sold 4 Bays, was its 6 5/8" whiskers length and small (non continuous) reflector screen. Like all commercially sold 4 Bays (before the DB4e), it was optimised to peak between RF60 and RF70, and also like the other commercially sold 4 bays it has phase lines for aprox 8" bay spacing, that favored mid to high UHF channels.
The old DB4's REAL world performance at this location was still "very good". keeping in mind it was rated (and marketed) as a moderate range antenna.
It was not intended for deep fringe reception. When I had the stock DB4, I did not have any weak UHF channels below RF31 to test it on, but RF38 (-8db NM 2 edge 114 miles TVFools) did come in constantly around SNR25-27, day and night with the old stock DB4.
When discussing how much on par the old DB4 is versus "other 4 Bays", we are talking about what, a grand total of 2 other antennas now being built by major manufacturers not called Antenna Direct? The 4221HD and HD4400
Unfortunately, I did not have access to the 4221HD model to compare versus the old DB4, but I did have the HD4400. The old DB4's real world performance at this location for deepest fringe RF38, RF39, and RF48 was about on par with the "out of the box" HD4400.
I did not have any weak (and reliable) lower UHF channels (below RF30) to test and compare. Today (post digital conversion), is a different story. Example, RF21 repeater station (3.5KW ERP, -24db NM, 57 miles, 1 edge according to TV fools), is now available. This weak 1 edge channel comes in reliably day and night with the modified DB4. Longer whiskers (now 8 3/4") and larger 36" curved reflector screen yes, but still with the old DB4 phase lines for 8" bay spacing.
When you are talking about antennas with only 1-3 db "modeled" difference, other factors can have a MUCH larger impact on real world performance (such as finding the best sweet spot on your property, optimum balun selection and minimising losses downsteam of the antenna).
Lastly, by next summer, I plan on installing a test setup that will allow the swapping of antenna's in about 5-10 minutes without the need to climb ladders. Anyone in the Vancouver area, is welcome to private message me about bringing over ANY UHF antenna to test and compare.