PreAmps

[KingCobra_CDX882]

Hey All...

A good thing about this forum is ability to get others views on things...
i will also post this in antenna section for is related to there as well..

What are the best Pre Amps to use for say..
2 meters
1.25 meters
70CM band
23CM band

Not that it matters too much..
but using with
Icom 706 MKIIG
IC-7000
IC-910H (getting within 3 to 6 weeks)

with dual polarity 9 element beam for 2 meters on 17.5 ft boom
with 12 element horizontal beam for 1.25 meters on 12 ft boom
with 16 element horizontal beam for 70 cm band 12.5 ft boom
nothing yet for the 23 cm band but would be beams ofcourse


Later

 

[Beetle]

With all that antenna gain, what do you need a preamp for?

 

[Moleculo]

Seriously...I'm with Beetle on this one. Can you tell us what you're trying to accomplish on top of all that antenna gain?

 

[KingCobra_CDX882]

it is simple..

i talk further then i can hear..
so my reason for looking into a preamp is to hear further
to know and converse with those who may hear me but i not hear them....pretty simple

i was hoping one would mention the only usable preamps
those not attached to radio or part of radio..

rather PreAmp attached directly to the antenna
such a preamp gets the signal before coax loss and radio loss
so should be able to act as successfull preamp and not simply boast static..but boost a clean signal to be heard better


Thanks

 

[Captain Kilowatt]

it is simple..

i talk further then i can hear..
so my reason for looking into a preamp is to hear further
to know and converse with those who may hear me but i not hear them....pretty simple

The solution is quite simple.Run lower power.

Actually try www.downeastmicrowave.com/ and click on their online catalogue.They have everything you would need in the way of transverters,preamps etc.

 

[nomadradio]

For those bands, conventional wisdom is to mount a preamp at the antenna end of the coax. This way, BOTH the preamp's internal noise AND the desired signal are both attenuated by the long run of coax. This vastly improves the ratio of desired signal to the preamp's internal noise. Putting a receiver preamp at the bottom end of the coax is far less effective at 2 meters and above.

Down East Microwave should have some explanations of this concept, along with ways to switch the preamp OUT of line before your transmitter RF can smash it coming up the coax. Making the relay in the preamp switch over to "standby" so your transmit signal can pass through it has to be done before the otherwise toxic transmit power can damage it.

Kinda like comedy. Timing is everything.

73

 

[Captain Kilowatt]

Nomad that is true about where and why to mount a preamp but if you have REALLY good cable it makes no discernable differance.See my comments where this is ALSO posted in the Meters, Accessories, & Test Equipment forum. FYI it is a pain to have to follow a thread about the same topic when it is posted in several places.Let's try to post a topic ONCE and leave it at that please. :roll: This is the THIRD place for this topic here.

 

[TonyV225]

If you were having trouble hearing depending on the situation or problem I would think that A receive amp may still leave you in the same boat as far as hearing or even create a new problem and that would be bringing in static or noise that would most likely cover up the low level signal you are trying to receive> Although this may be a horse a piece and on those bands i generally quiet but that receive amp may just bring in a level of noise to cover those signals your trying to hear up. If its quiet for the most part then Ide say give it a try but if it were me I would find someone that had an rf amplifier to try ouit before spending $$$ on one.

 

[Beetle]

"i talk further than i can hear."

At any given time, how can you possibly know that?

 

[Captain Kilowatt]

Tony, preamps for the VHF/UHF bands are an entirely differant breed from CB preamps

Here is a cut and paste from my post in the OTHER forum where this is addressed:

I must say that first there are preamps on CB amps and then there are real preamps.The preamps in CB amps are,for the lack of a better word,garbage.They will make the S meter read higher but will also amplify the noise level.Some of the transistors used in those "preamps" actually have a higher noise floor than the radio they are connected to which means that given a quiet freq. and a very weak signal you may be able to hear better without the preamp despite the higher signal reading on the meter.A "real" preamp has a low noise transistor usually a GAsFET type.Some have bandpass filters built in to allow for a rejection of out of band signals that could swamp the rx.One common misconception is the use of a preamp to hear a station better over the noise or QRM.THAT DOES NOT WORK! A preamp is best used on a quiet freq. to bring a very weak signal up over the noise floor of the radio.Weak signal VHF/UHF is where they REALLY shine.I have a GAsFET preamp in my Mirage 2m amp and even though it is in the shack and not at the antenna it works wonders.The fact I use Andrews 1/2 inch heliax means that I am losing almost nothing before the preamp anyway. It's almost like having the preamp at the antenna anyway.KingCobra if you use that type of cable or better,and I believe you do,don't worry about where to put the preamp.Lightning can and will take them out fairly easily and one in the shack at the end of a GOOD cable can be protected by simply unhooking the cable,something you cannot do if it is mounted at the antenna. Here is something you can try.Point your antenna at the sun which is a huge emitter of wideband RF.If the noise increases then you have enough gain already.

 

[jonbah]

I use gasfet mast mounted pre-amps for small signal VHF-UHF work Sats and SSB they make a world of difference for this type of application.

 

[KingCobra_CDX882]

Hey All..

Ok now i am getting a litle better info on these style of preamps

in answer to how i might know i can not hear as far as i talk
i say so for if i hear someone i am able to get to them..
it is rare that if i hear someone that i can not get to them
so logic dictates i am talking further then i could hear..

i did not think of lightning damage
so far (as i knock on wood)
i have not had lightning hits..

coax is fairly good
Andrews Heliax LDF5-50A
likly switching to LDF7-50A and will use smaller for HF

also i suspected it would only work on a quieter band
reason i am asking this
i am getting Icom 910H
which on its own should do better then either the 706 MKIIG or
IC-7000 (although i have not had time to use IC-7000 much yet)..
the 910H lists as accesories these PreAmps
i also am looking into for 1.25 meters

i know of downeastmircowaves
had i gone the route of the TS-2000
i likly would have bought their 222 transconverter that hooks up extremly easily to the TS-2000

now i need go back to see their PreAmps

anyways

i was curious to know how it works in regards to transmit posibly messing up the preamp

i see is a lot more intailled in mounting it at the antenna
will a high end PreAmp really work as well between the radio and coax in my shack..
thereby easing additional mounting and better lightning protection

and sorry posting in 3 sections
wasnt sure what section would have been the best

Thanks

 

[TonyV225]

QRN That was an awsome explanation. I know the setups for these bands are more costly and when you spend that kind of money its nice to know that what you are doing is really making a difference and yes as far as preamps on Amps in 10 11 12 meters they might as well leave them out I never use them there nothing but noise amplifiers. I may also have some question on these gas charges lightning arrestors. Anyways thanks for the info Im actually gonna save that

 

[trash]

I use
a dual gate 3SK121 for 2m. (SSB)
a dual gate BF904 for 70cm (ATV)
a single gate MGF1302 for 13/23cm (ATV)

I don't know what your motives are, usually EME is the reason for running low noise pre-amps. But ATV they are important too.

 

[KingCobra_CDX882]

well...


talking repeaters is fine..
but like trying to get out further on SSB
also interested in EME and sat stuff


Later