hey guys what do you all think is better for a uhf repeater on gmrs a folded dipole such as a db-408 or a fiberglass antenna?
otto
folded dipole or fiberglass omni
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bayfire300
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Tom in D.C.
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- What radios do you own?: Progreso soup can with CRT
Which type antenna?
A folded dipole won't provide any gain unless you stack two or more
of them. A fiberglass antenna, in some configurations, will provide
gain, and on UHF you can get a lot of gain with a relatively small
antenna. OTOH, the stacked dipoles can be made somewhat
directional wheras the fiberglass antenna will most likely have an
omnidirectional pattern.
It depends mostly on what you want and need and can afford.
of them. A fiberglass antenna, in some configurations, will provide
gain, and on UHF you can get a lot of gain with a relatively small
antenna. OTOH, the stacked dipoles can be made somewhat
directional wheras the fiberglass antenna will most likely have an
omnidirectional pattern.
It depends mostly on what you want and need and can afford.
Tom in D.C.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
In 1920, the U.S. Post Office Department ruled
that children may not be sent by parcel post.
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bayfire300
- Posts: 348
- Joined: Tue May 17, 2005 5:19 pm
thanks guys for your input........i was told a folded dipole was a true repeater antenna and although a fiberglass would work it wasnt ideal.
i'll keep the antenna i have which is a comet gp-9nc its dual band but tuned for commercial.i also like it's performance i was just wondering if i should have went w/ a folded dipole.
thanks again
otto
i'll keep the antenna i have which is a comet gp-9nc its dual band but tuned for commercial.i also like it's performance i was just wondering if i should have went w/ a folded dipole.
thanks again
otto
Folded dipoles or fiberglas collinear....
Since I fell in love with the DB-420, I will choose that antenna over a fiberglass collinear any day.
I love the mechanical design of the DB-408 and DB-420, they are very 'quiet' antennas due to direct D.C grounding, whereas the collinear builds up noise from the radome and is vulnerable to total destruction if struck by lightning.
The DB-408/420 phasing harnesses are completely weather sealed as they are molded to provide a weather tight shield and are U.V resistant as well.
The DB-408 has moderate gain and can be 'adjusted' for different patterns such as omni, cardioid or 'directional' by element placement.
I have only one problem with the DB-420 antenna; it's very hard to find one that is tuned for the amateur band, and most are designed for 450-470 Mhz. ranges.
You can use the 450-470 design on 440, but your radiation pattern will be higher than expected but still well within a usable range.
You may have to special order phasing harnesses for the DB-420, whereas you can probably purchase the DB-408 already tuned for the 440 band.
You can 'tune' a fiberglass collinear with strips of aluminum foil wrapped around the radome, but you will have to set the antenna up off the ground by at least 5 feet to eliminate ground reflections.
The trick works very well and you will probably have to use several 3" wide strips once you locate the initial SWR changes with a single 'test' wrap of foil.
Take one wrap of foil on the antenna, transmit into the antenna and watch the SWR reading as you slide the foil up and down the antenna.
When you get the lowest SWR reading, tape the foil to that spot and make a new strip and begin again to obtain the lowest possible reading.
Once all tests have been done and you have the lowest possible SWR reading, you can coat the strips with varnish to weather seal them and make them permanent.
These strips do not affect the antenna's radiation pattern or performance at all, so don't worry about destroying your pattern.
It's a cheap and very effective means to use out of band fiberglass antennas on the amateur band.
This trick works for most fiberglass collinears that are tuned ABOVE the amateur band, I have not tried this 'trick' on antennas tuned below the amateur band yet personally, so I can't comment about the effectiveness of performing this 'modification'.
Of course, you can't do this on the DB-408/DB-420.
For a quieter site, I would choose the DB-408 over the fibergass collinear especially if the tower site's grounding is unknown.
You can't have too much grounding capability.
Precipitation static is annoying with fiberglass antennas.
(edited to correct information that was improper)
I love the mechanical design of the DB-408 and DB-420, they are very 'quiet' antennas due to direct D.C grounding, whereas the collinear builds up noise from the radome and is vulnerable to total destruction if struck by lightning.
The DB-408/420 phasing harnesses are completely weather sealed as they are molded to provide a weather tight shield and are U.V resistant as well.
The DB-408 has moderate gain and can be 'adjusted' for different patterns such as omni, cardioid or 'directional' by element placement.
I have only one problem with the DB-420 antenna; it's very hard to find one that is tuned for the amateur band, and most are designed for 450-470 Mhz. ranges.
You can use the 450-470 design on 440, but your radiation pattern will be higher than expected but still well within a usable range.
You may have to special order phasing harnesses for the DB-420, whereas you can probably purchase the DB-408 already tuned for the 440 band.
You can 'tune' a fiberglass collinear with strips of aluminum foil wrapped around the radome, but you will have to set the antenna up off the ground by at least 5 feet to eliminate ground reflections.
The trick works very well and you will probably have to use several 3" wide strips once you locate the initial SWR changes with a single 'test' wrap of foil.
Take one wrap of foil on the antenna, transmit into the antenna and watch the SWR reading as you slide the foil up and down the antenna.
When you get the lowest SWR reading, tape the foil to that spot and make a new strip and begin again to obtain the lowest possible reading.
Once all tests have been done and you have the lowest possible SWR reading, you can coat the strips with varnish to weather seal them and make them permanent.
These strips do not affect the antenna's radiation pattern or performance at all, so don't worry about destroying your pattern.
It's a cheap and very effective means to use out of band fiberglass antennas on the amateur band.
This trick works for most fiberglass collinears that are tuned ABOVE the amateur band, I have not tried this 'trick' on antennas tuned below the amateur band yet personally, so I can't comment about the effectiveness of performing this 'modification'.
Of course, you can't do this on the DB-408/DB-420.
For a quieter site, I would choose the DB-408 over the fibergass collinear especially if the tower site's grounding is unknown.
You can't have too much grounding capability.
Precipitation static is annoying with fiberglass antennas.
(edited to correct information that was improper)
Last edited by AEC on Sat May 13, 2006 11:13 pm, edited 1 time in total.
A DB-420 is a monster folded dipole antenna, think of the DB-408 on steroids and you're close.
The 420 has twice the dipole elements the 408 has, and weighs close to 50 pounds due to the heavy two- piece mast and the added phasing harnesses, but most are tuned for the 450-470 Mhz. range but can be ordered for the 440 band at of course, an extra cost.
If I remember the documentation, the antenna had 9dB of gain in an omnidirectional pattern as you stagger the dipoles from top to bottom in 90 degree increments.
I had two of these antennas years ago and used then on both of my ham repeaters, and I can tell you they worked GREAT!
A test was done running the MSY at exciter output of 10 watts and the machine in north Racine, we drove to the north end of Milwaukee and even at a distance greater than 50 miles, we could still access the repeater and hear the output well above the noise floor!
I had an ARR GaAs FET preamp and a six cavity BpBr duplexer.
I could use the repeater at over 40 miles away using my GP-300 at the time, also with very little noise on my signal.
I am sorry I sold those antennas, they were the best I've ever had, and they stood up to 50+ MPH wind storms and ice as well.
Extremely rugged antennas, I'll buy them if they ever come up for sale in this area, no matter how many are available, I'll try to buy them all.
You wil NEVER go wrong with the DB-420 on UHF, they are superb!
(edited to correct improper information)
The 420 has twice the dipole elements the 408 has, and weighs close to 50 pounds due to the heavy two- piece mast and the added phasing harnesses, but most are tuned for the 450-470 Mhz. range but can be ordered for the 440 band at of course, an extra cost.
If I remember the documentation, the antenna had 9dB of gain in an omnidirectional pattern as you stagger the dipoles from top to bottom in 90 degree increments.
I had two of these antennas years ago and used then on both of my ham repeaters, and I can tell you they worked GREAT!
A test was done running the MSY at exciter output of 10 watts and the machine in north Racine, we drove to the north end of Milwaukee and even at a distance greater than 50 miles, we could still access the repeater and hear the output well above the noise floor!
I had an ARR GaAs FET preamp and a six cavity BpBr duplexer.
I could use the repeater at over 40 miles away using my GP-300 at the time, also with very little noise on my signal.
I am sorry I sold those antennas, they were the best I've ever had, and they stood up to 50+ MPH wind storms and ice as well.
Extremely rugged antennas, I'll buy them if they ever come up for sale in this area, no matter how many are available, I'll try to buy them all.
You wil NEVER go wrong with the DB-420 on UHF, they are superb!
(edited to correct improper information)
Last edited by AEC on Sat May 13, 2006 11:15 pm, edited 1 time in total.
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bayfire300
- Posts: 348
- Joined: Tue May 17, 2005 5:19 pm
Sinclair
SRL310C series. Now called a SD310-H for single
http://www.sinctech.com/catalog/group.aspx?id=2
SRL310C series. Now called a SD310-H for single
http://www.sinctech.com/catalog/group.aspx?id=2
My BIG BOO-BOO...it IS a DB-420 I was trying to describe, but was caught up with the '412' use for some unknown reason.mastr wrote:It sounds as if you are describing a DB420 to me.
I caught my mental infarction when I read my post again this evening.
But I doubt this will result in a Geico commercial though.
Thanks for catching my mistake...I know others should have as well.
What is your experience comparing the DB-410 to a DB-408? My site is going to be around 700' HAAT and I am going to be at the 125' level on the tower in addition. Tower is a 3 leg free-standing Rohn 300' tall. Going to be side mounted on NE leg with a nice standoff mount. Looking for coverage of 20 miles all directions with an HT. Location is in mountains of NC. Marion to be precise. Receiver is going to be a Mitrek and feedline will be 1 5/8" that is already on the tower. Can't beat that deal! Still trying to decide the pre-amp situation out. Can't decide which one to order
On that note does anyone know where there are some used DB-408 or 420 antennas at, that someone would be willing to ship either via ups or freight line? I get a discount with either company. Would be nice if someone on here got a gold discount from Tessco and would let me pay them to order a new antenna at the gold rate. They are not that expensive when you get the gold discount! Thanks ahead of time
On that note does anyone know where there are some used DB-408 or 420 antennas at, that someone would be willing to ship either via ups or freight line? I get a discount with either company. Would be nice if someone on here got a gold discount from Tessco and would let me pay them to order a new antenna at the gold rate. They are not that expensive when you get the gold discount! Thanks ahead of time
I have worked on Folded Di-Poles and Fiberglasses, and have used both as well. I seem to notice a better signal/range on a folded di-plole (Stacked+Angled) than I would a fiber glass. I tested the range on a GR1225 and MTR setup (2 Different antennas, 1 fiberglass one dipole) and got a better report on the dipole.
That's just my experience.
That's just my experience.
Ah, no I wasn't. The Sinclair antennas are rated in dBd.RFGuy is talking dbi,while all other references were in dbd.just wanted to clear that up.
mod
Here is the cut and paste from the Sinclair spec sheet:
SD310-H Series
1 dipole antenna, 2.0/1.5 dBd gain, HD, Covers 370-512MHz in 2 band splits
SD312-H Series
2 dipole antenna, 4.0/4.8 dBd gain, HD, Covers 370-512MHz in 2 band splits
SD314-H Series
4 dipole antenna, 8.0/8.5 dBd gain, HD, Covers 370-512 MHz in 2 band splits
SD318-H Series 8 dipole antenna, 9.3/10.2 gain, HD, Covers 370-512 MHz in 2 band splits
The other nice thing on the Sinclair folded dipole is a single antenna covers 406 to 512 mHz. Great for multicoupling.