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post #1 of 17 Old 01-29-2015, 03:19 PM - Thread Starter
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Foster City, CA - Antenna Setup for two towers 180° apart from eachother

Hello All,

Was hoping someone could recommend an antenna configuration given that I am located right in the middle (or pretty close to middle) between two adjacent city transmission towers. I'd like to get signals from both towers.

I want to either get:

A) one DB4 antenna without a reflector (I'm thinking this may have one tower's signal interfere with the other)

-OR-

B) two back-to-back DB4s separated by a reflector (thinking that the reflector will prevent interference from each tower's signal )

Attached is my TV Fool Radar details link and an illustration detailing my two options.

http://www.tvfool.com/?option=com_wr...2c151b634c3377

Currently I have an DB4 antenna setup indoors and gets good reception but I am planning to put an antenna on the roof for more channels and stronger signals.

Thanks.
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post #2 of 17 Old 01-29-2015, 06:53 PM
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You might want to consider posting this on the San Francisco OTA forum where there are more Bay Area people who will see it.

Here's your corrected TV Fool link:

http://www.tvfool.com/?option=com_wr...2c151b634c3377

Your signals are so strong that you may be able to get away with a simple antenna with no reflector. It's definitely preferable to mount such an antenna outdoors to minimize indoor reflections.

Two antennas back-to-back is really the same thing as one antenna with no reflector. Channels 7 and 11 are so strong you can likely receive them on a UHF antenna.

What concerns me is that the Bay Area has a lot of reflections because of the hills which could cause problems with a bi-directional antenna. You can try it and see what happens. You're lucky that Mt. San Bruno and Sutro Tower are only 10 degrees apart from Foster City.
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post #3 of 17 Old 01-29-2015, 06:56 PM
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Quote:
Originally Posted by Nik Kershaw View Post
Sorry for posting the URL like that but AVS Forum didn't grant me enough permissions to post the link correctly stating I didn't have enough posts. Funny how I read the sticky and the sticky stated to post link to TvFool.com for your first post.
The sticky also says to PM Dr. Don to do it for you if you don't have enough posts. Your title should say Foster City instead of Bay Area.
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post #4 of 17 Old 01-29-2015, 09:35 PM - Thread Starter
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Thanks Calaveras!

Appreciate your input on this and posting the link to TV Fool for my area (I managed to get the permissions and made the update to original post). I'll go with purchasing a single DB4 without reflector and see how it works.

I didn't post this in the SF OTA section because I was more interested in the DB4 performance characteristics; namely, is having a single DB4 without reflector is the same as having two back-to-back DB4s sandwiching a reflector to get a bi-directional antenna? I thought that the reflector would shield each opposing signals from being interrupted.

Looked at your DTV page, that is some setup and you get channels from towers that are 110 miles from you.

Quote:
Originally Posted by Calaveras View Post
Your signals are so strong that you may be able to get away with a simple antenna with no reflector. It's definitely preferable to mount such an antenna outdoors to minimize indoor reflections.

Two antennas back-to-back is really the same thing as one antenna with no reflector. Channels 7 and 11 are so strong you can likely receive them on a UHF antenna.

Last edited by Nik Kershaw; 01-29-2015 at 09:43 PM.
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post #5 of 17 Old 01-29-2015, 09:56 PM
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Quote:
Originally Posted by Nik Kershaw View Post
I didn't post this in the SF OTA section because I was more interested in the DB4 performance characteristics; namely, is having a single DB4 without reflector is the same as having two back-to-back DB4s sandwiching a reflector to get a bi-directional antenna? I thought that the reflector would shield each opposing signals from being interrupted.
When you put antennas back to back like that and then sum them together with a 2-way combiner it's pretty much like not having the reflector. All sorts of experiences have been reported combing two antennas but the most common outcome is for some stations from both directions to come in and some stations that were fine with just one antenna are lost. The typical recommendation is an A/B switch or a rotor.
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post #6 of 17 Old 01-29-2015, 10:05 PM
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Channel Master CM 3020 UHF / VHF / FM HDTV Antenna - 100 Mile Range (CM3020) is latest TV antenna of 2015.. Its installation is very easy.. I put this antenna up last weekend and I am receiving about 60 channerls, but it still works excellent in my area.. At first I had issues regarding setting and installation of this TV antenna
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post #7 of 17 Old 01-30-2015, 09:15 AM - Thread Starter
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Quote:
Originally Posted by Calaveras View Post
When you put antennas back to back like that and then sum them together with a 2-way combiner it's pretty much like not having the reflector. All sorts of experiences have been reported combing two antennas but the most common outcome is for some stations from both directions to come in and some stations that were fine with just one antenna are lost. The typical recommendation is an A/B switch or a rotor.
That is the exact information I was hoping to get. You saved me a tons of time and money in conducting the trial and error process for my setup. Even with my current setup, I am getting all the channels I want. I was leaning towards the over-engineered route (back-to-back setup) and I am sure I would have lost some channels--I'm guessing from the 2-way combiner I would experience some signal loss and other strange behavior with this configuration.

So a big thanks again.
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post #8 of 17 Old 01-30-2015, 09:22 AM - Thread Starter
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Quote:
Originally Posted by Gooppoiner View Post
Channel Master CM 3020 UHF / VHF / FM HDTV Antenna - 100 Mile Range (CM3020) is latest TV antenna of 2015.. Its installation is very easy.. I put this antenna up last weekend and I am receiving about 60 channerls, but it still works excellent in my area.. At first I had issues regarding setting and installation of this TV antenna
Not sure if this has anything to do with this post, but thanks. FYI, that antenna seems to be a uni-directional antenna and my setup requires pulling signals from opposing 180º directions (bi-directional). Besides, that antenna would be too large for my taste and would require a rotary thingy and perhaps putting two of these CM3020 up which is something I didn't want to deal with.
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post #9 of 17 Old 01-30-2015, 09:44 AM
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If you ask a Carpenter how he would approach a job, he would immediately grab his Hammer.
If you ask a Surgeon how he would cure a sore throat, he would immediately grab his Scalpel.
If you ask the owner of a Monster Antenna what he recommends.....you get the drift....

Your STRONG Signals have a wide spread in arrival directions, which means DB-4 (e???) is a good choice for UHF.
As you concluded, a Monster Antenna would need to be constantly rotated to bring the Narrow Beamwidth on Target.

HOWEVER, the NEW DB4e uses a Printed Circuit Board (PCB) Balun that severely attenuates VHF signals (Ch2-13).
Although the CM3020 receives these signals, it is a huge overkill....but you MIGHT need some sort of VHF Antenna.

A-D sells a Dipole/Rabbit-Ears Kit (with VHF/UHF Combiner) for attachment to C2, DB-4e and other Antenna....it's Bi-Directional, but it's designed for Hi-VHF Band (Ch7-13) and has some Gain, but poor SWR on Ch2-6....so those channels may or may NOT come in....and provides provides NO Suppression of Multipath:
https://www.antennasdirect.com/store...rofit-Kit.html

IF you MUST receive any of the channels from Ch2-Ch6, you'll probably need a VERY WIDE Antenna that covers all the way down to Ch2, in addition to DB-4's for UHF. Since DB-4e probably isn't adequate for these channels, I recommend you consider and try ONE (OR TWO Vertically Stacked) Moderate Gain Ch2-13 Lo/Hi-VHF Antenna(s), such as $30/ea Antennacraft CS600. VHF/UHF Combiner(s) (A-D, R-S or UVSJ) is used to sum together VHF signals for each of the two Separate UHF Coax Downleads going to an RF A/B Switch--so Multipath picked up and ENHANCED by one Antenna does not degrade the Other:
http://www.antennacraft.net/pdfs/CS600.pdf
If you use TWO CS600's they and the DB-4e's should be connected to SEPARATE Coax Downleads and connected to an RF A/B Switch (R-S make one with Remote Control capability).

If DB-4e isn't adequate for Hi-VHF Channels and you can live without Ch2-6, you might need just ONE (no Ch7-13 to South) Moderate Gain Ch7-13 Hi-VHF Antenna, such as $30 Antennacraft Y5-7-13:
http://www.antennacraft.net/pdfs/Y5-7-13.pdf

Last edited by holl_ands; 01-30-2015 at 10:43 AM.
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post #10 of 17 Old 01-30-2015, 04:13 PM - Thread Starter
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Thanks holl_ands. I didn't even consider a DB4e, is there a significant difference between a DB4e and a DB4?

Thanks.
Quote:
Originally Posted by holl_ands View Post
Your STRONG Signals have a wide spread in arrival directions, which means DB-4 (e???) is a good choice for UHF.
As you concluded, a Monster Antenna would need to be constantly rotated to bring the Narrow Beamwidth on Target.

HOWEVER, the NEW DB4e uses a Printed Circuit Board (PCB) Balun that severely attenuates VHF signals (Ch2-13).
Although the CM3020 receives these signals, it is a huge overkill....but you MIGHT need some sort of VHF Antenna.

Last edited by Nik Kershaw; 01-30-2015 at 04:18 PM.
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post #11 of 17 Old 01-30-2015, 06:20 PM
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Quote:
Originally Posted by Nik Kershaw View Post
Thanks holl_ands. I didn't even consider a DB4e, is there a significant difference between a DB4e and a DB4?

Thanks.
I think he means DB8e. The DB8e has moveable halves so you can point it in two different directions. There will still be the same problem though with possible loss of stations because each half will be receiving reflections which might interfere with the main signal from the other half. It's something you just have to try. It's not easily predictable. I would point a small high VHF antenna at 315° for 7 and 11 and use a VHF/UHF combiner for the two antennas.
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post #12 of 17 Old 01-30-2015, 11:45 PM
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The DB-4 is A-D's OLD model that was designed to operate on the OLD UHF Band, up thru Ch69, which resulted in much lower Gain on lower channels than their NEW DB-4e. Model for OLD DB-4 model shows a sharp dropoff in Raw Gain on lowest UHF Channels, very poor mid-band SWR and F/B & F/R minimum of about 15 dB:
http://imageevent.com/holl_ands/mult...ayrefl/db4refl

Since DB-4 has been discontinued and is very difficult to locate, I presume you will be looking to buy the NEW DB-4e model, which thus far is the ONLY Commercial 4-Bay that has been redesigned for the NEW UHF Band, which provides more Gain on BOTH Ch14 and Ch51, while maintaining the wide beamwidth typical of 4-Bay Antennas:
https://www.antennasdirect.com/cmss_...s/DB4E-TDS.pdf
There are TWO versions: DB-4e is the standard model and DB-4 PRO (mysteriously WITHOUT the "e") is the more expensive Heavy Duty (tested to 80 mph) model for Professional Installations that you'll find on A-D website. I didn't see the lower cost model on A-D website, but it's readily available from a variety of sources:
http://www.amazon.com/Antennas-Direc.../dp/B0074H3IU6
http://www.walmart.com/ip/Antennas-D...tenna/22087581

DB-8e is a pair of DB-4e's on a mount that allows them to be oriented any way you want, including opposite directions....in either a side-by-side arrangement (shown in Installation Instructions) or one to each SIDE, with some distance between the two. The cost is significantly LESS than a pair of DB-4e's:
https://www.antennasdirect.com/store...V-Antenna.html
http://www.amazon.com/Antennas-Direc.../dp/B00C4XVOOC

If you intend to NOT use separate Coax Downlead's and an A/B Switch, I would guesstimate that two back-to-back DB-4e's would provide significantly more "isolation" than either configuration using DB-8e (if it even makes any difference). But I haven't done the simulations to make sure....and would need to use something "similar" like the CM4221HD or DIY M4 model, since I/we don't have a model of the A-D Antennas. [And a single DB-4e WITH Reflector REMOVED could do the same thing.]

Last edited by holl_ands; 01-30-2015 at 11:55 PM.
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post #13 of 17 Old 01-31-2015, 01:36 AM - Thread Starter
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Ok, based on your input, sounds like I'll be getting an DB-4e and removing the reflector.

Thanks for your time and input. It was very informative.

Quote:
Originally Posted by holl_ands View Post
The DB-4 is A-D's OLD model that was designed to operate on the OLD UHF Band, up thru Ch69, which resulted in much lower Gain on lower channels than their NEW DB-4e. Model for OLD DB-4 model shows a sharp dropoff in Raw Gain on lowest UHF Channels, very poor mid-band SWR and F/B & F/R minimum of about 15 dB:
http://imageevent.com/holl_ands/mult...ayrefl/db4refl

If you intend to NOT use separate Coax Downlead's and an A/B Switch, I would guesstimate that two back-to-back DB-4e's would provide significantly more "isolation" than either configuration using DB-8e (if it even makes any difference). But I haven't done the simulations to make sure....and would need to use something "similar" like the CM4221HD or DIY M4 model, since I/we don't have a model of the A-D Antennas. [And a single DB-4e WITH Reflector REMOVED could do the same thing.]
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post #14 of 17 Old 01-31-2015, 01:40 AM
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BTW: When you remove the Reflector from a 4-Bay Antenna, you might consider replacing the A-D PCB Balun with the usual Cylindrical 300:75-ohm Transformer Balun, which will restore the Hi-VHF Performance inherent in the DB-4e, which MIGHT be adequate for your Hi-VHF Channels...although it's still not as good as a dedicated Hi-VHF Antenna, such as Y5-7-13.

WITHOUT the Reflector, I would expect that the UHF performance (and with Balun Replacement, Hi-VHF Gain of about 3.5 with low SWR) will be about the same as mclapp's M4 (DIY Kit is available), which is also Optimized for the NEW UHF Band:
http://imageevent.com/holl_ands/multibay/4bay/superm4
http://imageevent.com/holl_ands/mult...y/super4m10x95

Last edited by holl_ands; 01-31-2015 at 01:52 AM.
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post #15 of 17 Old 02-27-2015, 03:42 AM - Thread Starter
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Quote:
Originally Posted by holl_ands View Post
BTW: When you remove the Reflector from a 4-Bay Antenna, you might consider replacing the A-D PCB Balun with the usual Cylindrical 300:75-ohm Transformer Balun, which will restore the Hi-VHF Performance inherent in the DB-4e, which MIGHT be adequate for your Hi-VHF Channels...although it's still not as good as a dedicated Hi-VHF Antenna, such as Y5-7-13.

WITHOUT the Reflector, I would expect that the UHF performance (and with Balun Replacement, Hi-VHF Gain of about 3.5 with low SWR) will be about the same as mclapp's M4 (DIY Kit is available), which is also Optimized for the NEW UHF Band:
http://imageevent.com/holl_ands/multibay/4bay/superm4
http://imageevent.com/holl_ands/mult...y/super4m10x95
Just an update, I did what you suggested and am very happy with the results. Thanks again for your time and input.
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post #16 of 17 Old 02-28-2015, 03:36 PM
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It's unclear as to which approach you chose.....removing DB4e reflector or just the M4 Bowtie Kit???
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post #17 of 17 Old 03-05-2015, 04:28 PM
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Quote:
Originally Posted by Gooppoiner View Post
Channel Master CM 3020 UHF / VHF / FM HDTV Antenna - 100 Mile Range (CM3020) is latest TV antenna of 2015.. Its installation is very easy.. I put this antenna up last weekend and I am receiving about 60 channerls, but it still works excellent in my area.. At first I had issues regarding setting and installation of this TV antenna
Good lord, thats a thing of beauty, looks like it would pick up everything! I have a similar issue to the OP, in that I want to pick up US stations (south) and Canadian stations (north), and it looked like the DB8 was a better choice as this one is very directional apparently.

Last edited by CanadaJimmy; 03-05-2015 at 04:31 PM.
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