pre amps for 2m pre amp or LNA

2m & 70cm discussion - antennas, propagation, operating, etc
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pre amps for 2m pre amp or LNA

Postby VK3MEG » Fri Jul 29, 2016 12:19 pm

looking at preamps for 2m possibly 70cm this is where my station has been lacking lna seem a good alternative at a reasonable cost.
do i mount it in the shack or on the tower my biggst issue is the long run to the top of the tower 30-40m mainly rg 213 cant justify the upgrade to lmr 400 just yet my main iterests are hf and 6m. and the lack of activity on 2m shows my hestiance. my antenna is 9 element lfa @ 11m 70cm qrt atm ( 13 element atn yagi for 70cm unreliable lookign at makign a yu7ef 18-20element for 70 cm). rig ic 7100 with a possiblity of a transverter for my elad sdr for 2m down the track and small rm italy amp for 2m 100w pep. my antenna's would be limited to a max 11 elements possibly stacked but i figured the pre amp will help b4 going the antenna upgrade path evn though my station is in a good postion contacts have been limited to 7-800 klm hoping to stretch that a bit further in the summer i have just heard the vk6 beacon when it was in over summer. thought idea's are welcome
cheers
steve
de vk3meg
cheers
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Re: pre amps for 2m pre amp or LNA

Postby VK2EFM » Fri Jul 29, 2016 12:49 pm

Hi Steve,

Mount the PreAmp/LNA at the antenna. You are using the amplifier to overcome the loss of the coaxial cable and the Noise Figure (NF) of your radio. Google Friis Law.

Basically you will be going from a NF of (Cable loss + Radio Noise Figure) to NF of PreAmp. Also you need enough gain to overcome the cable loss and radio NF and no more.

73,
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Re: pre amps for 2m pre amp or LNA

Postby VK3DXE » Sat Jul 30, 2016 1:22 am

Steve, have a look at Wimo http://wimo.com/mast-preamplifier_e.html#mastvorverstaerker

The Mini 2 and Mini 70 offer reasonable performance at reasonable cost. Certainly better performance and prices than a 2nd hand Icom masthead LNA. You won't lose money on either of these units if you get the bug and decide to go bigger and better (bigger being power handling capability).

Get it as close as practical to the antenna for best performance, but you don't have to be completely anal about it, especially on 2m. Even 10m from the antenna is a bucket load better than your current 30 - 40m.
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Re: pre amps for 2m pre amp or LNA

Postby VK3MEG » Sat Jul 30, 2016 7:55 am

thanks guys it has given me good idea's
cheers
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Re: pre amps for 2m pre amp or LNA

Postby VK5PJ » Sat Jul 30, 2016 8:08 am

Steve,
if you are not scared by a soldering iron, have a look at the minikits selection. http://www.minikits.com.au/electronic-kits/rf-amplifiers/rf-preamplifiers he has a switched version for most bands and a case to put them in (GME TV mast head case) so it ends up being quite economical and the satisfaction of doing it yourself. He also has a BIAS T kit there so you can inject DC up the coax to power the beast.

Not build one myself but gave them serious consideration.
Peter Sumner, vk5pj
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Re: pre amps for 2m pre amp or LNA

Postby VK3ZAZ » Sat Nov 24, 2018 8:42 am

Got mast heads on all three bands now
great cost
great risk
on 23 worked 5PJ 3II 3AXH
that's it

$300 per qso so far
Tread your own path :om:
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Re: pre amps for 2m pre amp or LNA

Postby VK3ALB » Sun Nov 25, 2018 7:52 am

Hi Steve,

I'd go for the MiniKits based on value for money and availability. If it's like other Icom radios I'm pretty sure the 7100 has DC out the coax for powering preamps on 2m/70cm. I like the idea of mounting it in a GME box.
Lou - VK3ALB

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Re: pre amps for 2m pre amp or LNA

Postby VK4UH » Tue Nov 27, 2018 11:50 am

It was a hard concept to accept, at least I found it so, that the only benefit of a preamp, in terms of “system performance” is to overcome loss in the feeder on receive. Anything beyond that is little more than an Smeter amplifier.

So as the “law” above says it has to be as close to the antenna as possible and certainly at the top of the tower.

The hardest problem for a high performance antenna system is achieving the preamp gain and noise figure which can be bypassed effectively, with adequate isolation, for the safety of the preamp , when running high power as well.

The ultimate goal for optimum performance for terrestrial and celestial/EME work
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Re: pre amps for 2m pre amp or LNA

Postby VK4CDI » Tue Nov 27, 2018 2:15 pm

Have built my own for 2/70/23, but never got the expected results, probably lack of proper test gear. Bought preamps for 2/70 from Pete WA2ODO and G4DDK for 23 and 9cm.....brilliant...
With Pete's preamp, if you break them, send it back to him (unopened) and he will repair/retune free of charge, other than postage.....
See KL7UW page for a list of available preamps. No association with either Pete or Sam, just a happy customer.

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