Antennas Direct OTA Antennas & Gear - Page 30 - Canadian TV, Computing and Home Theatre Forums

lithOTA · 2012-05-15, 12:53 PM

ADTech, I just wanted you to see what kinds of crazy things people are doing to your "children"...

I was trying to use stagger-stacking to cancel out an offending co-channel from behind. It didn't work beacuse the power difference between the two stations is just too great, but the exercise did produce a big rear null on the target frequency and several stations a few channels away.
I'll say this about a pair of C2s (or a taken-apart C4)- they are great for experimenting with special combinations like stagger stacks and the "two-antenna trick" described on HDTV Primer.

roger1818 · 2012-05-15, 01:46 PM

^^^lithOTA, it may be just the angle the picture was taken at, but it doesn't look like the 2 coax feeds are the same length. Was this intentional? Normally you would want them the same length, unless they are carefully measured to phase shift one antenna, but I don't know why you would do both that and a stagger stack.

rabbit73 · 2012-05-15, 08:50 PM

The two lengths of coax must be different for stagger stacking to work properly.

I quote from pages 186-187 of TV Antennas and Signal Distribution Systems by M. J. Salvati:

"Stagger stacking is a special variation of vertical stacking in which one antenna is mounted one quarter wavelength ahead of the other (Fig. 8-8). The cable section connecting the forward antenna to the signal combiner is made an electrical quarter wavelength longer than the other so the signals from the front are combined in phase. Signals arriving from the back, however, are 180 degrees out of phase and thus cancel. This results in a very high front-to-back ratio, even if the front-to-back ratio of the antennas is very poor. When this technique is used on antennas having a high front-to-back ratio to begin with, the rearward pickup of the array is virtually zero."

I think lithOTA did a good job of using what he had on hand to make a valid test.

Well done, Mike!

roger1818 · 2012-05-15, 10:48 PM

^^^Oh, OK. That makes sense! Wouldn't you need to compensate for the velocity factor of the coax when making it 1/4 wavelength longer though? I guess that is what they mean by electrical quarter wavelength.

ADTech · 2012-05-16, 12:54 PM

Quote:

ADTech, I just wanted you to see what kinds of crazy things people are doing to your "children"...

Well, I'm more a "step-uncle" for most of these things... I'll show your photo to the "Daddy", he'll get a kick out of it.

Pretty cool!

rabbit73 · 2012-05-16, 07:27 PM

Quote:

Wouldn't you need to compensate for the velocity factor of the coax when making it 1/4 wavelength longer though? I guess that is what they mean by electrical quarter wavelength.

Yes, that's exactly what he did, using the velocity factor of 0.85 that was specified by the manufacturer of his coax.

The wavefront of the incoming signal arrives at the upper antenna sooner than the lower antenna, so you need the extra coax to act as a delay line so that the signals from the two antennas arrive in phase at the combiner.

roger1818 · 2012-05-16, 08:05 PM

^^^Sorry, I didn't see any mention of velocity factor in his original (or suubsiquent) posts.

rabbit73 · 2012-05-17, 02:30 PM

No problem; it took me a long time to go through his posts because I was very interested in high F to B ratios after trying to help Balm with VHF-hi WVNY reception at his summer cottage in Saint Anicet.

threeflags · 2012-05-28, 04:10 PM

How's the DB4e for FM reception. Seems to work but I'm noticeably missing 2 strong local stations from Toronto (about 40 miles away). From those nearby, the 2 stations are CHUM(104.5) and the Q107.

roger1818 · 2012-05-28, 04:44 PM

^^^The DB4e will be about as good for FM as it is for VHF-LO and that is very poor. Strong broadcasts will be receivable by anything, but you will be better off with a simple FM folded dipole.

ADTech · 2012-05-29, 12:12 PM

Roger is quite correct. UHF antennas will work for FM about as well as the power cord on your bedside clock radio. Short-range reception is usually okay, but beyond that, a real FM antenna should be used.

ppauper · 2012-05-30, 04:10 AM

I apologize if this is in the wrong thread

(US) Walmart is now selling 2 Antennas Direct HDTV antennas , ClearStream Micron and ClearStream1

Walmart Embraces Cord-Cutting Movement

ADTech · 2012-05-30, 10:49 AM

Please note they're being positioned in the aisle with the Roku-type products instead of with the other antennas and accessories.

Individual store setups may vary.

roger1818 · 2012-05-30, 11:15 AM

ADTech, any idea if it will come to Walmart Canada? It would also be nice if they sold the indoor C2 (and C2V) as well.

Blackburst · 2012-05-30, 11:20 AM

Need some advice for the DB2e and the DB4e

I've used a DB8 in the past. But since I've moved recently, I have a DB4 temporally placed at a window picking up all the Montreal stations (except for CFJP-DT 35.1) and also WCAX, WPTZ and WCFE from the US. Not bad really for a indoor window placement.

Summer time is here and it'll be time to do a proper roof top install. I'm in a Condo building that allows Dishes and such on the roof. So no problem.
But, at the same time, I would like to use a small footprint antenna on the roof.

The question is which one. Would a DB2e be good enough to replace a DB4, or would I require a DB4e instead. I won't use the DB4 I have as I have promised it to somebody else.

The set up would be on a six storey building. No obstructions, can see Mount Royal, and have a clear path towards the US. The only thing that concerns me is the airplane path as they prepare to land at the local airport. But that would be on the back end of the antenna. The RG6 run would be 6 floors down, and then another 30 to 40 feet back up.

Comments, Suggestions appreciated.

2012-05-15, 12:53 PM	#436
lithOTA Join Date: Jul 2010 Location: Lake in the Hills, Illinois Posts: 100	ADTech, I just wanted you to see what kinds of crazy things people are doing to your "children"... I was trying to use stagger-stacking to cancel out an offending co-channel from behind. It didn't work beacuse the power difference between the two stations is just too great, but the exercise did produce a big rear null on the target frequency and several stations a few channels away. I'll say this about a pair of C2s (or a taken-apart C4)- they are great for experimenting with special combinations like stagger stacks and the "two-antenna trick" described on HDTV Primer. __________________ TV Fool Report: http://www.tvfool.com/?option=com_wr...4033e5a566a704

2012-05-15, 01:46 PM	#437
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,613	^^^lithOTA, it may be just the angle the picture was taken at, but it doesn't look like the 2 coax feeds are the same length. Was this intentional? Normally you would want them the same length, unless they are carefully measured to phase shift one antenna, but I don't know why you would do both that and a stagger stack. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-05-15, 08:50 PM	#438
rabbit73 DHC Supporter Join Date: May 2010 Location: S.E. VA Posts: 181	The two lengths of coax must be different for stagger stacking to work properly. I quote from pages 186-187 of TV Antennas and Signal Distribution Systems by M. J. Salvati: "Stagger stacking is a special variation of vertical stacking in which one antenna is mounted one quarter wavelength ahead of the other (Fig. 8-8). The cable section connecting the forward antenna to the signal combiner is made an electrical quarter wavelength longer than the other so the signals from the front are combined in phase. Signals arriving from the back, however, are 180 degrees out of phase and thus cancel. This results in a very high front-to-back ratio, even if the front-to-back ratio of the antennas is very poor. When this technique is used on antennas having a high front-to-back ratio to begin with, the rearward pickup of the array is virtually zero." I think lithOTA did a good job of using what he had on hand to make a valid test. Well done, Mike! __________________ If you can not measure it, you can not improve it. Lord Kelvin, 1883

2012-05-15, 10:48 PM	#439
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,613	^^^Oh, OK. That makes sense! Wouldn't you need to compensate for the velocity factor of the coax when making it 1/4 wavelength longer though? I guess that is what they mean by electrical quarter wavelength. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-05-16, 08:05 PM	#442
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,613	^^^Sorry, I didn't see any mention of velocity factor in his original (or suubsiquent) posts. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-05-17, 02:30 PM	#443
rabbit73 DHC Supporter Join Date: May 2010 Location: S.E. VA Posts: 181	No problem; it took me a long time to go through his posts because I was very interested in high F to B ratios after trying to help Balm with VHF-hi WVNY reception at his summer cottage in Saint Anicet.

2012-05-28, 04:10 PM	#444
threeflags Join Date: Jan 2011 Location: Newmarket - North of Toronto Posts: 54	How's the DB4e for FM reception. Seems to work but I'm noticeably missing 2 strong local stations from Toronto (about 40 miles away). From those nearby, the 2 stations are CHUM(104.5) and the Q107.

2012-05-28, 04:44 PM	#445
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,613	^^^The DB4e will be about as good for FM as it is for VHF-LO and that is very poor. Strong broadcasts will be receivable by anything, but you will be better off with a simple FM folded dipole. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-05-29, 12:12 PM	#446
ADTech Join Date: Oct 2010 Location: Antennas Direct Tech Support - St Louis Posts: 212	Roger is quite correct. UHF antennas will work for FM about as well as the power cord on your bedside clock radio. Short-range reception is usually okay, but beyond that, a real FM antenna should be used.

2012-05-30, 04:10 AM	#447
ppauper Join Date: May 2007 Posts: 212	I apologize if this is in the wrong thread (US) Walmart is now selling 2 Antennas Direct HDTV antennas , ClearStream Micron and ClearStream1 Walmart Embraces Cord-Cutting Movement

2012-05-30, 10:49 AM	#448
ADTech Join Date: Oct 2010 Location: Antennas Direct Tech Support - St Louis Posts: 212	Please note they're being positioned in the aisle with the Roku-type products instead of with the other antennas and accessories. Individual store setups may vary.

2012-05-30, 11:15 AM	#449
roger1818 Veteran Join Date: Apr 2006 Location: Ottawa (Stittsville), ON, OTA (Radio Shack Omnidirectional Antenna and 5Y6S in Attic), MythTV HTPC Posts: 5,613	ADTech, any idea if it will come to Walmart Canada? It would also be nice if they sold the indoor C2 (and C2V) as well. __________________ Link to my TVFool results is in my profile Homepage URL. I suggest others do the same.

2012-05-30, 11:20 AM	#450
Blackburst Join Date: Dec 2007 Location: Saint-Laurent Borough, Montreal, QC Posts: 804	Need some advice for the DB2e and the DB4e I've used a DB8 in the past. But since I've moved recently, I have a DB4 temporally placed at a window picking up all the Montreal stations (except for CFJP-DT 35.1) and also WCAX, WPTZ and WCFE from the US. Not bad really for a indoor window placement. Summer time is here and it'll be time to do a proper roof top install. I'm in a Condo building that allows Dishes and such on the roof. So no problem. But, at the same time, I would like to use a small footprint antenna on the roof. The question is which one. Would a DB2e be good enough to replace a DB4, or would I require a DB4e instead. I won't use the DB4 I have as I have promised it to somebody else. The set up would be on a six storey building. No obstructions, can see Mount Royal, and have a clear path towards the US. The only thing that concerns me is the airplane path as they prepare to land at the local airport. But that would be on the back end of the antenna. The RG6 run would be 6 floors down, and then another 30 to 40 feet back up. Comments, Suggestions appreciated.

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