Re: [Repeater-Builder] Side mounted DB-224 for omni coverage?
kc4fwc wrote: Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? The issue is how far the antenna is from the tower. You need to be about one wavelength away from the tower to get close to an omni pattern from a side-mount. Doesn't matter if it's VHF, UHF, SHF, whatever. Pointing the elements into the tower will give you something funky, depending on the shape of the tower and so on. For a 2M repeater, push the antenna out about 5-6 feet from the tower. -- Jim Barbour WD8CHL Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] Side mounted DB-224 for omni coverage?
Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] Side mounted DB-224 for omni coverage?
We have done that here with a DB-224 and 3 DB-268s and we seem to have a pretty good omni pattern. These are side mounted on 6 ft stand-offs on a Rohn 80 tower. Jamey Wright Systems Analyst Morgan County EMCD 911 Decatur, Al 256-552-0911 -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of kc4fwc Sent: Friday, August 12, 2005 4:08 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Side mounted DB-224 for omni coverage? Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Side mounted DB-224 for omni coverage?
I think you would need Decibels 5 foot (60) off the tower side mount to make a reasonably true omni pattern out of that. kc4fwc wrote: Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Side mounted DB-224 for omni coverage?
Here is how my DB-224 was done. You mount it one wave length off the tower at the transmit frequency. Point all four dipoles at the tower. Funny how it works but it will give you near omni for a pattern. This is in the standard antenna placement book for RF engineering. It works well. I have four in our network like this. 1 two meter and 3 222 MHz repeaters. Good luck and 73, Russ, W3CH - Original Message - From: kc4fwc [EMAIL PROTECTED] To: Repeater-Builder@yahoogroups.com Sent: Friday, August 12, 2005 5:08 PM Subject: [Repeater-Builder] Side mounted DB-224 for omni coverage? Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] Side mounted DB-224 for omni coverage?
Probably mounting it further away from the tower will reduce the nulls. Turning the dipoles all one direction into the tower has the effect of directionalizing the pattern and pointing it into the null. When you directionalize, you get about 9 db gain toward the direction of the dipoles and loose 3 db the other way (you still have an average of 6 db). So if you turn the dipoles all toward the tower, you should reduce the null by 3 db but you also reduce coverage in the other direction by 3 db, assuming everything else remains the same. The gain off the sides will not change much and just interpolate in between. I would try it because such a big difference between transmit and receive can be very annoying. For short towers (less than 500 feet or so), I prefer to use the top antenna for receive since it is more irritating to be able to hear the repeater and not get in than vice-versa. Dave Baughn Director of Engineering The University of Alabama Center for Public Television and Radio Box 870150 Tuscaloosa, Alabama 35487 205.348.8622 cell 205-310-8798 NEW EMAIL [EMAIL PROTECTED] [EMAIL PROTECTED] 08/12/05 04:08PM Hello Group, Have a dual antenna system for a 2M repeater. Decibel DB-222 top mounted, clears the tower and is oriented for omni-directional coverage. TX antenna is directly below and is side mounted on the southwest side of the tower. The antenna is a Celwave PD-340-3 with dipoles oriented around the mast (omni). It is mounted on the corner (not the face) of Rohn 25-G and is a factory mount and top sway brace from Decibel Products and they recommend this for side mounting DB- 224's. The mount lets the antenna extend around 22 inches from the leg of the tower. I am noticing VERY significant deficiencies in TX coverage back through the tower, even what I would estimate 8 to 10 dB. In other directions, it seems as if the coverage is as good as can be predicted. I have heard someone mention that taking all four dipoles on the same side of the mast and directing the elements straight into the tower would create more of an omni pattern. I can't remember if this was for UHF or VHF. I would like to eliminate any deep nulls, no more than 3 dB down in any direction if possible. Will turning all elements towards the tower help my situation? Yahoo! Groups Links Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
