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RX pre amps

JohnE

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JohnE Enthusiast

JohnE

Posted
Posted

putting this out there again

these are RX only amplifiers

 http://www.anglelinear.com/

one of the best out there for commercial or HAM. I have these in multiples in many sites, low noise high gain.

http://www.downeastmicrowave.com/

mostly HAM related stuff but makes a nice pre amp for commercial use. again low noise high gain. I have one of these on my private repeater and works great.

http://www.advancedreceiver.com/

had a few of these over the yrs but found they over load pretty easily in high RF environments. on the plus side they make an inline RF switched pre amp that will handle up to 160W. very nice for control or mobile application.

all of these either use GasFet, PHEMT or EPHEMT devices. the old bi-polar transistor types are still out there but have a much higher noise figure.

I also suggest that these be used w/pass/notch filters w/better than 100dB of isolation between the ports.

17 answers to this question

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Logan5 Newbie

Logan5

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Posted

PastorGary, are these mast mounted preamps, to be used in a repeater environment? or for a dedicated scanner or simplex radio antenna? I have used a mast mounted TV preamp in the past, but that is a receive only application. Myself an another myGMRS user have done a few radio checks today and I am thinking a RX pre might help, or maybe wait till I get a new repeater? we are working with 25 watt's at 40' and can't get past 10 miles over flat Florida, anyway were gonna raise it 10 more feet tomorrow. well see how that goes.  Best Regards Jim....

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PastorGary Newbie

PastorGary

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Posted

PastorGary, are these mast mounted preamps, to be used in a repeater environment? or for a dedicated scanner or simplex radio antenna? I have used a mast mounted TV preamp in the past, but that is a receive only application. Myself an another myGMRS user have done a few radio checks today and I am thinking a RX pre might help, or maybe wait till I get a new repeater? we are working with 25 watt's at 40' and can't get past 10 miles over flat Florida, anyway were gonna raise it 10 more feet tomorrow. well see how that goes.  Best Regards Jim....

 

Jim - If you check with the originator of this thread up in Post # 1, I'm sure that John can answer your questions. I am not involved in RX preamps and have never seen one in operation.

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JohnE Enthusiast

JohnE

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Logan5

  ARR makes 2 types of rf switched pre amps, one is a tower mount that can handle 160W the other is a smaller indoor 25W version. these are ok for mobile or control set ups.

on a repeater the RX only pre amps increase RX sensitivity. on my stand alone private repeater (tkr850) the front end opens at 0.25uV, w/DEI pre amp in line it will do 0.12uV. in terms of dB that is a 6dB increase and when on the fringes or noisy areas it makes a difference of being heard or not.

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JohnE Enthusiast

JohnE

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passing on that Chip from Angle linear had closed up shop and gone fishing.

sad to see him go as he had some of the best preamps and duplexers around not to mention his technical expertise in the field.

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ASRM Newbie

ASRM

Posted
Posted

Post Resurrection  :)

 

I have my repeater up and running, range is good at 40 feet, actually surprised. I have some areas that the portable or mobile will key the repeater but is scratchy or choppy (every other word or will break squelch but not the repeater), will a pre-amp in the receive side help the signal be more solid and clear, I figure that the signals in the noise will not be pulled out, but looking for a way to make the signals I can hear be more clear.

 

I know I would need to replace the duplexer since I am using one of the "mobile type" duplexers, the $150-$300 kind.

 

I also realize raising my height will help, goal is 60-70 feet, and upgrade the antenna from the Comet 172 (9dbi/6.5-7db) to a more commercial DB stacked dipole or a decent fiberglass at 7-9db. 

 

Thanks in advance.

 

(If I should have started a separate thread I can remove and start a new one)

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Logan5 Newbie

Logan5

Posted
Posted

for the cost, I think good quality feed line and keeping feed line length minimal would be better. if your feed required coax in lengths over 100' might consider a preamp. but unlikely to do much if you already have a quality setup to begin with. 

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ASRM Newbie

ASRM

Posted
Posted

The repeater is a Vertex VXR7000, I had the shop go over it real hard and he was happy, desense was perfect in his eyes, I have a 30 foot mast mounted on the top of the porch, so an effective 40-42 feet, I have 40 feet of 1/2 inch heliax, using n-connectors on the antenna, a Comet CA-172EFC, that goes thru a lightning arrestor into n-connectors with a small 1 foot jumper to the repeater, the duplexer is mounted in the repeater, kicking about 35 watts out. The Comet is a 9dbi, which I am told is really just a 6 or 7 db gain antenna.

 

As I said, the range is similar to what was predicted via the propagation app, my mobiles do well with an effective 15-20 miles, as expected deep cuts and valleys can be scratchy, portable is good in a car for about 5 to 7 miles, some spots can be almost 10-15, at my job, mobile is good, portables will break squelch but not the PL for the repeater (about 12 miles out). 

 

Just looking to squeeze all I can until I can get some better height with a 60 foot tower with a 10 foot mast or maybe 20, and possibly go for a DB408, the 420 is out of my price range, I would effectively be just at tree top at the base of the antenna, have a lot of pines around me being out in the country.

 

http://i641.photobucket.com/albums/uu140/aussierescueil/Base%20antenna%202.jpg

I should quantify that my repeater seems to get similar range to the other GMRS repeaters operating in my area. 

 

I am happy with the results of my little project, the system is my answer to SHTF prep communications, like tornados and extended power outages (zombies would be another matter ;) We lost cell service in the Washington tornado for hours (need to read up on the solar post more) and couldn't reach family what so ever, towers were down, running out of power, etc. It was a very big eye opener.

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Logan5 Newbie

Logan5

Posted
Posted

I was running that exact same comet antenna, I swapped it out with a Browning Yagi 10.2db, considering my lack of height, the yagi helped overcome some LOS issues.

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zap Newbie

zap

Posted
Posted

I was running that exact same comet antenna, I swapped it out with a Browning Yagi 10.2db, considering my lack of height, the yagi helped overcome some LOS issues.

There is an article on RBTIP about using a yagi array for an omni directional pattern.

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