Antennas Direct OTA Antennas & Gear

[Stereocraig]

For whatever reason, AD, your post regarding the combiner box, was not visible to me when I was typing.

I have disassembled this C4 and am currently fitting 1/2 of it as the feed for a 10' parabolic, as in the CM4251 thread and will be trying out the other half on a 7.5 footer.
I was referring to the screws on one of the loops itself, as I have since tossed the combiner in the parts bin.

All in all, I really can't complain about what I paid for this kit, regardless of what I may need to do to it.
It's still a good base to work from.

[lithOTA]

Thanks AD, I will get that done one of these days.

But since I have the cable method going, I decided to play with the "Two Antenna Trick" as descibed by Ken Nist. I didn't have time yet to make a custom cross-brace, so I just left the separation at the stock 16.5 inches.
I figure that if I can get the lobes to spread 60-90 degrees from each other, I would be able to ditch the switch and grab 3 cities from one feed. As I went through the stations and noted signal strength and RF channel, I could see that the lower UHFs (up to about RF30) were really strong, but up high (above RF40) they were weak because the lobes are not split far enough.
I will use a piece of firring strip and one of the C4's mast clamps to make a new cross-brace. I can then experiment with different separation dimensions by simply screwing the C2s into the firring strip. From the looks of Ken Nist's graph, I think 15 inches might do the trick.

[threeflags]

Originally Posted by HWP

Well, I'm interested in getting a new DB4e. I'm going to do a shootout with a 4221hd on a roof-peak satellite mount. I'll test each antenna with and without a pre-amp and post the results on DH.

I hope I can get one before it's too cold to go up on the roof.

...

Just wondering if you gotten a chance to do the shoot out?

Thanks.

[Aburgdxer]

I am also interested in buying a DB4e and would be very interested in your results.

[re_nelson]

I am also interested in buying a DB4e and would be very interested in your results.

I did a shootout between three AntennasDirect UHF (91XG vs. C4 vs. DB4e) antennas a few weeks back.

http://digitalhome.ca/forum/showthread.php?t=148520

DHC member lithOTA provided a chart showing a comparison between the three.

[dragon_eater]

Referring to ADTeck's post #310, which shows the horizontally stacking of two DB4e's.

Question 1) Upon review, I can not find/see any cross-over phase lines in an individual DB4e...instead there exists 2 feed points (in parallel) between each each pair of bow-ties...am I correct?

If the latter is true, (i.e. twin feed points fed by parallel phase lines), then in constructing this 8 bay (2 horizontally stacked DB4es), could not one use, the then now resulting 4 feed points, connect them in parallel (using 300 or 450 ohm wire of equal lengths) to a single central point, as physically in the center of this resulting new 8 bays, and accounting for parallel resistance, use a 1 to 1 balun of 75 ohms, instead??

[ADTech]

Question 1) Upon review, I can not find/see any cross-over phase lines in an individual DB4e...instead there exists 2 feed points (in parallel) between each each pair of bow-ties...am I correct?

Yes, that's correct.

[dragon_eater]

ADTech, question for you; since a DB4e (for all intensive purposes) is the electrically parallel connection of two vertically stacked DB2e's, would not the resulting parallel connection result in one-half the overall impedance, whereby the resulting balun (used on a DB4e) would actually be a 150 to 75 ohm or 2 to 1 balun? Again, I am assuming that each DB2e, is operating at the 300 impedance range for UHF.

[ADTech]

Since antennas are rarely ever perfectly 300 ohms in the real world, we simply accept that the impedance match can never be perfect. We measure the return loss (VSWR) and do the best to keep mismatch losses below a certain level (see spec sheet).

For all intents and purposes, it's as close as it's going to get in a consumer product.

would not the resulting parallel connection result in one-half the overall impedance,

Seems like that's what I recall from basic AC Circuits from a long time ago.

[holl_ands]

When two 300-ohms 4-Bay antennas are interconnected by a Feedline, it acts as
a Transformer, resulting in a combined impedance of 300-ohms when done properly:

mclapp's M8 Vertical 8-Bay:
http://m4antenna.eastmasonvilleweath...dels%20M8.html
http://m4antenna.eastmasonvilleweath...y/8%20bay.html
http://m4antenna.eastmasonvilleweath...se%20lines.pdf

And of course side-by-side 4-Bays (e.g. 2X CM4221HD) and typical 8-Bay antennas:
http://imageevent.com/holl_ands/multibay/8bayrefl

[leszek]

Where I live I have 4 VHF-hi stations. So I decided to add the $20 C2v VHF kit to the DB4e. I used the existing holes and supplied hardware. It works quite well allowing me to receive those 4 stations that I had dropouts before. I did not notice any degradation on the UHF stations, so I'm a happy camper.

[Maury Markowitz]

Hi, Leszek. Is the VHF kit the single dipole in the picture? If so, that's rather simple, and I might consider adding it to my rig.

Does it mount directly to the existing antenna? Or is it generic, so it could be used with any antenna?

[ADTech]

Maury,

The C2v Reflector kit can be disassembled and hacked to resemble the photo in post #294 of this thread. The kit is all screws and nuts as fasteners - no rivets, so it's easy to take apart.

Forum sponsor Save n Replay recently ordered 20 of the conversion kits. They should be available by now.



Leszek,

Would you mind posting a TVFool plot so we can see what's around you? Much appreciated!

[leszek]

My TvFool report:

http://www.tvfool.com/?option=com_wr...0b860ce0ca3e20

My "DB4e-V" antenna is pointed at ~200° and I get everything in the green and yellow zones. If I point the antenna at ~320° I get the stations in the red zone but loose some in the yellow zone and when it came to PBS vs. MeTV, PBS won. I did buy 42XG that I will point to ~320° to get MeTV and CoolTV in the near future. The full list of stations in my area can be found at http://members.shaw.ca/nwbroadcasters/digitaltv.htm

[leszek]

Originally Posted by Maury Markowitz

Hi, Leszek. Is the VHF kit the single dipole in the picture? If so, that's rather simple, and I might consider adding it to my rig.

Does it mount directly to the existing antenna? Or is it generic, so it could be used with any antenna?

Yes it is a simple dipole and it's generic enough to be mounted by itself in any manner you wish. In fact the C2V kit is vey complete and comes with the dipole, UHF/VHF combiner a screen and even a mast mount + all the screws you need, so you can use it as a standalone VHF antenna right out of the box.