problem with pre-amp

[cassidy1190]

I just purchased an 800MHz antenna from radio shack and since the trunked system I'm trying to receive doesn't come in well i also got a pre amp. My reception with the 800Mhz antenna didn't come in so good as i expected so i turned on the pre amp. To my surprise this just made it worse. That doesn't make any sense because aren't amplifiers supposed to improve reception? What is going on?

 

[xusmarine1979]

The problem I had with the pre-amp on 800 is picking up all that noise and interference. One of the more expereinced guys should be able to give ya a link so you can get a filter. I think the ScannerMaster site at the top of the page may sell them.

 

[cassidy1190]

Im not recieving anything at all though when i turn on the pre-amp. Mabey im getting overload, i doubt that though since im barley getting any reception in the first place...

 

[cassidy1190]

Im not recieving anything at all though when i turn on the pre-amp. Mabey im getting overload, i doubt that though since im barley getting any reception in the first place...

 

[N_Jay]

Im not recieving anything at all though when i turn on the pre-amp. Mabey im getting overload, i doubt that though since im barley getting any reception in the first place...

Do a search on pre-ampos, and read all the posts.

In general, they do not help much, and can often reduce reception.

In some cases thay can help, but for scanner listeners it is the unusual case.

 

[xusmarine1979]

When I had mine it did awesome on UHF and VHF. Just not too hot on 800.

 

[LarrySC]

First radio rule of thumb. The best amp is the correct antenna. Amps work in special conditions only. Usually retail amps have 20db gain. In your application maybe 1db to 2db would be max. I installed a GRE amp for Skywatch Traffic for an 800 system 30 miles away using a 6db gain yagi antenna pointed that direction and an 80' run of RG-8 coax. The gain antenna boosted signal for the coax run and the amp runs at 50% or about 10db max. In this installation it works perfect. If your amp has a fixed gain and you cant adjust it, the thing may never give good service. Good Luck, Larry

 

[cassidy1190]

I actually do haver a GRE amp with 20db gain. I can also adjust the amount of db, but it seems that the higher i go the worse the reception gets. This goes for 800MHz, UHF, and VHF too...

 

[xusmarine1979]

Sounds like overload. The exact same problem I was told that I had. Try using the stock rubber duckie with the amp.

 

[W4KRR]

I actually do haver a GRE amp with 20db gain. I can also adjust the amount of db, but it seems that the higher i go the worse the reception gets. This goes for 800MHz, UHF, and VHF too...

The solution is to forget about the pre amp. As you have seen, they often overload the radio and make reception worse than no antenna at all. Like Larry said above, a good antenna is the best solution-without the pre amp!

 

[N_Jay]

The solution is to forget about the pre amp. As you have seen, they often overload the radio and make reception worse than no antenna at all. Like Larry said above, a good antenna is the best solution-without the pre amp!

A good antenna WITH good cable!

 

[cassidy1190]

I actually do have a good discone, with LMR-400 cable (only 10 ft). I figured the 800MHz antenna would obviously be best for 800MHz. I am probably too far from a reapeter or something. Some days are always better than others too so its not all that bad. If u have any suggestions to improve my reception though fell free to let me know...

 

[TeRayCodA]

Only 10 ft? how high is the other 800 Mhz antenna?

Like NJay said,the coax is also the key.LMR 400 is good,low loss. May need more elevation.

I tried a pre-amp once,sent it back,refund.It's like on a tv,if at first you have a snowy picture,the amp will amplify the "snow"

 

[rhutch]

I have the Watson preamp and it works great. Adds approx. 2 bars to the signal strengthe of both the vhf and 800 Mhz trunked systems that I scan. The one system I can't even receive with-out the pre-amp. That being said when I was Toronto the pre-amp was really of no assisstance at all. I thinh they are worth experimenting with if you are in marginal signal areas.

 

[Al42]

I thinh they are worth experimenting with if you are in marginal signal areas.

You should also know where the 'marginality' is coming from. If you listen to my scanner stream (see my sig), you'll hear a lot of noisy signals. But I can't improve them - the repeaters are hearing the portables badly. (I get the same noise with a 13 element beam aimed at the repeater and 20 feet of LMR600.)

 

[flyingwolf]

Rememebr the coders creed.
Garbage in, Garbage out.
If the signal your getting is on the edge and when it comes in its clear but it just needs some help then a n amp MAY halp you.

However if your signal is noisy then you will simply be amplifying the noise.

As its been said. the best cure is a good antenna.

 

[Al42]

If the signal your getting is on the edge and when it comes in its clear but it just needs some help then a n amp MAY halp you.

However if your signal is noisy then you will simply be amplifying the noise.

Well ...

If the noise figure of the preamp is better than the noise figure of the receiver front end, the preamp will help dig the signal out of the noise a bit.

As its been said. the best cure is a good antenna.

No argument with that.

 

[wesct]

if you add a preamp, too much gain will give the results that you are getting. the receiver is sensitive enough- with the preamp, you are bringing up the noise floor. gain above 13 db is mostly noise.

wesct

 

[Al42]

gain above 13 db is mostly noise.

Where did you get that figure? Is that true for any preamp, regardless of the noise figure? Is it true for any receiver?

 

[N_Jay]

Where did you get that figure? Is that true for any preamp, regardless of the noise figure? Is it true for any receiver?

No, it is not true for any receiver, any noise figure amp, or any environment.

It was one person's guess based on their experience.