2-meter Preamp?
 

I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ

2-meter Preamp?
 

"998cc" wrote in
et:

I am looking for ways to improve my receive for 2-meter SSB weak
signal work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I
understand mast mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Russ, you may find the article at http://www.vk1od.net/gt/index.htm of
interest. It includes a model framework to allow you to calculate the
improvement that you would obtain from a LNA.

One thing to bear in mind is that laboratory tests of LNAs do not usually
revean the amount of noise that will be generated in the LNA as a result
of intermodulation processes... so it is unlikely to perform quite as
well as indicated. At the same time, the same issue exists for the
transceiver.

The good thing is that your 5WL Yagi will have a good deal of selectivity
whereas it is certainly lacking in the '706IIG and in many of the lower
cost preamps (no money wasted on filtering).

At the end of the day, it depends very much on your own noise
environment, noise generated by IMD in your radio, and the equipment
configuration. Hams tend to regard ambient noise as not an issue on
144MHz, but it probably is if you live in a residential area... and high
ambient noise will limit the benefit of a LNA.

Owen

2-meter Preamp?
 

Russ,

I have used both Landwehr and ARR preamps for 2 meter SSB. One of the
major issues is how much coax, and what quality, you have. Another is
the quality of the preamp which you have in your rig. In my case, I
have about 70' of very low loss coax, almost hard line in performance.
The preamp in my rig is fairly good, and the result is that there is
little difference in performance, though there is a slight nod to the
mast mounted unit. Lossy coax would definitely tip the choice to the
mast mount. And in fact, on 70 cms with equivalent components, the
mast mount is the clear winner. Beware of units which don't give you
noise figures, as that is normally much more important for weak signal
work than gain.

--
Alan
WA4SCA

2-meter Preamp?
 

On Tue, 23 Oct 2007 03:20:50 GMT, "998cc" wrote:

I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ

Am just today experimenting with satellie in-line amplifiers,
the variety for home sat reception, cheap, small.

Some range from 100 MHz to 2,4 GHz, some have limiting
filters on the input which you can easily remove or modify.

Works.

w.

2-meter Preamp?
 

I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ


There are 3 factors that determine if a preamp will help: does the radio
have poor sensitivity to start with, do you have significant feeder loss,and
how high is your ambient noise floor.

Taking the first and last together; no matter how good a pre-amp you use it
will be of no help if you have a high ambient noise floor to start with.
This is governed by where you live, quite country locations are obviously
much better than cities. As a quick check, see on ssb if your noise floor
drops significantly when you disconnect your aerial.
If it does then it is worth doing a better check where you compare the noise
between the aerial and a good dummy load. If the noise still drops
significantly then you are limited by the external ambient noise and all a
preamp will do is amplify this noise. If is does not change then you either
have a quite location or a noisy receiver.

If you are not limited by external noise then a preamp may help if you have
a lot of feeder loss, but the pre-amp must be at the antenna end, and not
the radio end, to improve things (unless you have a very very deaf
receiver).

In any case keep the gain of the preamp as low as possible that is still
consistent with improving the noise floor in order to limit problems with
receiver overload.

73
Jeff

2-meter Preamp?
 

"998cc" wrote in message
et...
I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ

It may not be worth the bother for low power. The receive preamp won't help
them hear you any better. At a KW output, you would want to do it for sure.
Meanwhile, make sure you are using low loss coax. That will help both
receive and transmit.

Tam/WB2TT

2-meter Preamp?
 

Owen Duffy wrote:
"998cc" wrote in
et:



The good thing is that your 5WL Yagi will have a good deal of selectivity
whereas it is certainly lacking in the '706IIG and in many of the lower
cost preamps (no money wasted on filtering).

I suspect the preamp makers would portray this as providing more system
engineering flexibility, letting you, the system builder, decide how
much filter selectivity (and corresponding loss/degradation of NF) you want.

After all, if you were doing EME with a big array pointed up into the
sky, selectivity might not be such a big deal, but absolute lowest
system noise figure might be.

2-meter Preamp?
 

On Oct 23, 2:33 am, Helmut Wabnig hwabnig@ .- --- -. DOT .- t wrote:
On Tue, 23 Oct 2007 03:20:50 GMT, "998cc" wrote:
I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ

Am just today experimenting with satellie in-line amplifiers,
the variety for home sat reception, cheap, small.

Some range from 100 MHz to 2,4 GHz, some have limiting
filters on the input which you can easily remove or modify.

Works.

w.

I used one of these "bullet" preamps once upon a time and the the
improvement in reception was amazing, too amazing.This was a give away
clue that my coax was bad. When I cut the bottom end off about a cup
of water came out of it

Jimmie

2-meter Preamp?
 

998cc wrote:
I am looking for ways to improve my receive for 2-meter SSB weak signal
work. I am running an Icom 706 MkIIG and a M2 5WL yagi. I understand mast
mounted preamps bring the signal up significantly.
Doe any one here use one for 2M SSB? What are your experiences?

Thanks
Russ


Russ- You may improve your senseitivity to a degree, with a preamp,
but it may (or may not) be worth the effort. As the mast mounted
preamp will establish your Rx noise figure, but, the ONLY advantage
from the GAIN of the preamp, would be to overcome the (Coax Loss,+
the Xcvr front end Noise Figure)-
This assumes that the preamp has a Noise Figure LOWER than the rig
, as Lower loss (hardline )coax might be more beneficial!
- the rest of any gain will only
make your receiver subject to front end overloading , from nearby
STRONG signals! Futher, you must have SOMETHING to delay the
transmitter from keying (a " sequencer"), or you may destroy your
preamp, by transmitting into it! Question? What is the Fastest
fuse you can get? Answer: a Transistor! Another way to increase
sensetivity, is to narrow your receiver band width . Halve your
Bandwidth, gain 6 dB increase in senseativity (X-4). And, as a
reliatively good test as to HOW MUCH the preamp will improve your
reception, try this test: 1) attach a 50 ohm non inductive
resistor to your antenna connector, and note your NOISE LEVEL/
S-METER. 2) Now replace your dummy load with your antenna.
Did the noise /or S-METER INCREASE? If so, you are most likely
receiveing at your maximum senseativity. (IF the noise level stays the
same, you MAY make an improvement to your system, tho, HOW much,
is hard to say! Hope this helps-- Jim NN7K

2-meter Preamp?
 

Jim-NN7K . wrote in
t:

....
And, as a
reliatively good test as to HOW MUCH the preamp will improve your
reception, try this test: 1) attach a 50 ohm non inductive
resistor to your antenna connector, and note your NOISE LEVEL/
S-METER. 2) Now replace your dummy load with your antenna.
Did the noise /or S-METER INCREASE? If so, you are most likely
receiveing at your maximum senseativity. (IF the noise level stays the
same, you MAY make an improvement to your system, tho, HOW much,
is hard to say! Hope this helps-- Jim NN7K

It is a relatively simple matter to measure the ambient noise level. The
ambient noise level is one of the factors that is vital to understanding
the benefit of a given preamp.

A simple test along the line of what Jim describes above, but leading to
a quantitative figure for ambient noise is described at
http://www.vk1od.net/sc/anc.htm , including a calculator to perform the
calculations.

Not many hams can tell you what their ambient noise level is on 144MHz,
but lots will wax on about the relative importance of LNA gain, LNA noise
figure, and cable loss. If you don't know the ambient noise level, you
cannot answer any of the other questions.

Note that ambient noise may change by hour of day and with antenna
pointing.

Owen