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Preamplifier at the antenna ??

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Christoph, DF9CY

Sun Jul 06 2008, 08:54AM
Hi all

is anyone using a (GaAs-Fet) preamplifier at the antenna ? Would it be good or is the noise already so high, that it would be a waste of effort - and money of course ? Some comments welcome ...

73 de Christoph
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Mark, CT1FJC
Sun Jul 06 2008, 09:54AM
Mark, CT1FJC
Registered Member #287
Joined: Sat Apr 19 2008, 12:14PM

Posts: 15
I use a Gasfet at the masthead and has proved useful when background noise is low and for EME. Under normal conditions here the difference is marginal. A lot depends on the Trncvr you are using of course. I have a TS-2000 and have the internal pre-amp switched off when using the Gasfet. To much gain is counter productive. 73 Mark CT1FJC
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Ken, G4IGO
Sun Jul 06 2008, 10:37AM
Ken, G4IGO
Registered Member #31
Joined: Tue Mar 18 2008, 08:16PM

Posts: 62
I have an LNA preamp - in the shack. I use it all time - debatable if useful for signals above S3 - but then I use EME and work EME type signals. I have also ts2000 - but i use preamps as well - no problem as far as i am aware. I do have LDF 5-50 feeder - so feeder loss is very very low. I would recommend using a preamp - under the right circumstances - but I would avoid all the complications etc. of mast head mounting. Also - I do not blow them up !! GL
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Brendan, G4DYO
Sun Jul 06 2008, 01:21PM
Brendan, G4DYO
Registered Member #441
Joined: Sat May 24 2008, 06:56PM

Posts: 42
I always thought - and have preached this elsewhere - that preamps should be up at the antenna. Is this not the case with modern gear?
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Per, LA7DFA
Sun Jul 06 2008, 04:54PM
Per, LA7DFA
Registered Member #189
Joined: Sun Apr 06 2008, 04:05PM

Posts: 44
Preamps should be closest possible to the feedpoint. Ken only have marginal losses with his high quality feedline, so having preamp indoor does not matter too much.
If you have 1dB in cable losses and a indoor preamp, it would equal the same as using a masthead preamp with 1dB higher noise figure.
With a proper sequencer and using relays with high isolation (e.g. 60dB) you will never blow your preamp.
The benefit of using a preamp depends on the local noise level.
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Robbie, Ei2iP
Mon Jul 07 2008, 05:53PM
Robbie, Ei2iP
Registered Member #19
Joined: Tue Mar 18 2008, 04:34PM

Posts: 9
Never used a Pre Amp for 50Mhz, I never felt the need to use one. My current qth is so quite, with only one birdie on 50.007.
With a pre amp too many 599 are reported which do not give a true reflection of an opening. If you can't hear them (DX) a pre amp is not going to be of much use.

Enjoy
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Trev, EA5ISZ
Mon Jul 07 2008, 06:14PM
Trev, EA5ISZ

Registered Member #13
Joined: Tue Mar 18 2008, 01:43PM

Posts: 143
I think we have touched on this subject before. I can categorically state that having used Peter G8BCGs set up in contests over several years, with a mast head pre-amp, the difference in readabilitity on weak signals is very significant. I would agree that a quiet location is probably necessary though.
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Mark, CT1FJC
Mon Jul 07 2008, 09:39PM
Mark, CT1FJC
Registered Member #287
Joined: Sat Apr 19 2008, 12:14PM

Posts: 15
Just a follow up to my previous.
Today I worked 48 USA stations with out my masthead pre-amp because of power line noise here.
Had the power line noise not been present and permitted the pre-amp use, I am sure that a few more, more distant squares could have been worked. Best thing is to have it available and use it when needed, like a good PA. 73
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Ken, G4IGO
Tue Jul 08 2008, 06:54AM
Ken, G4IGO
Registered Member #31
Joined: Tue Mar 18 2008, 08:16PM

Posts: 62
I think that all of the above posts cover it nicely - but I think Marks final comment is the best - and I would add - dont make too much work for yourself - the best preamp is none at all - having NO feeder loss - so the cheapest and best way is to invest your money in the shortest , least lossy coax you can - and remember that means ur TX signal is also better.
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Christoph, DF9CY
Wed Jul 09 2008, 04:56AM
Christoph, DF9CY
Registered Member #65
Joined: Thu Mar 20 2008, 04:27PM

Posts: 31
Thanks all here,
I think I will try out whether an antenna-mounted pre-amp will have any benefit for me. I have some on 2m and 70cm where they give good improvement. My TS690s' RX is quite sensitive and I can "see" noisy directions as well as galactic noise. I received a couple of EME (JT65A) signals in good quality too. All without a pre-amp. I will put one up, and make some careful comparisons. If it gives me any advantage in performance, it will stay up - otherwise it must go.
73 de Christoph

[ Edited Wed Jul 09 2008, 05:13AM ]
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