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

2-meter Preamp?
 

Jim Lux wrote in
:

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.

Hi Jim,

I suspect that was a bit tounge in cheek! I guess the manufacturers have
done us a bigger favour with hand helds in making them lighter by
minimising filtering.

If you want to fix an IC706IIG's front end selectivity here in Oz, one of
those Canadian filters for about $250 + $300 shipping is just the go.
Wait a minute, $550 to fix a $1000 radio's performance, and on just one
band... I don't think so.

I wrote an article on the performance of a modestly priced kit 144MHz
amplifier in the real world (as opposed to in a shielded room). I have
devised a test configuration that asseses what I term the 'realisable
sensitivity' which may be quite different to the specs derived in a
shielded room. The article is at http://www.vk1od.net/gt/144LNA/index.htm
..

The article also looks at the G/T improvements expected from other
configuration changes like a higher gain antenna and low loss coax, and
whether the preamp is located at the masthead or transceiver. Of course,
it all depends on one's own configuration, but the tools are there to
model a specific configuration.

Owen

2-meter Preamp?
 

Thank you Owen, Jim, Alan, Tam, Helmut, Jimmie and Jeff for all of the
great responses. I guess I should have provided more info
in the first post.

My station is in the foothills of Northern California at about 1200' elev
which is somewhat rural and is relatively quiet most of the time. Power
output is up to 500+ watts on VHF and the feedline to the antenna is about
90' of 1/2" Andrew Heliax hardline. The antenna is 43' up. Using my
previuos yagi, an M2 2M12, I worked stations as far as Oregon and San
Diego.

Good points on noise figures versus selctivity while considering noise floor
of the rig. I did try chercking the receiver noise with a Microlab dummy
load installed at the radio then with the antenna conneted. Yes, there is
more noise with the antenna connected. What is interesting is that with the
dummy load connected, the noise was just higher than wit the ope SO-239 at
the radio.

The responses have also steered my attention toward the 706G itself. While
it has been a great radio for several years, and offers fairly good
performance on many bands, designing this and similar multi-band radios
must include compromises. Perhaps I should be looking toward getting a rig
more tailored
to the 2m band and SSB mode? The Icom IC-910H comes to mind.

At this point, I will look more closely at the antenna/feedline system I
have and look into a better performing radio before investing in a
mast-mounted preamp that will introduce more connectors in the feedline and
which will likely require more maintenance as well.

Thanks again.
Russ W6OHM.

2-meter Preamp?
 

"998cc" wrote in
:

....
floor of the rig. I did try chercking the receiver noise with a
Microlab dummy load installed at the radio then with the antenna
conneted. Yes, there is more noise with the antenna connected. What

The higher the ratio of noise from the antenna to noise from the dummy
load, the less likely you are to get much benefit from a better receiver.

You need this ratio which tells you the ambient noise (albeit with IMD
noise rolled in) to predict how much a LNA or better receiver will
improved things.

Of course, by 'improve' I mean better S/N ratio, not simply higher S
meter deflection.

Alternatively, you suck it and see.

is interesting is that with the dummy load connected, the noise was
just higher than wit the ope SO-239 at the radio.

I assume that was to say "with the open SO-239".

I don't really know what you can conclude, because you don't know enough
about the radio when the input jack is o/c.

Owen

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

Stack another yagi so you can reply to what you hear.

2-meter Preamp?
 

"Hal Rosser" wrote in message
...

"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

Stack another yagi so you can reply to what you hear.


If he has room for it, this may very well be the best way to go. Gets away
from finding an amp that can take 500W on transmit, and does away with
complicated sequencing, which, if not done right could blow the amp if you
accidentally use VOX. For starters, replacing the 706 will probably result
in the best fun factor.

Tam/WB2TT

2-meter Preamp?
 

Stack another yagi so you can reply to what you hear.


If he has room for it, this may very well be the best way to go. Gets away
from finding an amp that can take 500W on transmit, and does away with
complicated sequencing, which, if not done right could blow the amp if
you accidentally use VOX. For starters, replacing the 706 will probably
result in the best fun factor.

Tam/WB2TT

Tam, that would be great, but I live in a community with CC&R's and antenna
restrictions. I was barely able to get permission for my single yagi by
using 911 and the Loma Prieta earthquake as bases for arguments. I really
don't want to push the issue too hard. I do agree that looking into a
better radio is probably the first step. If they made a VHF/UHF radio with
similar features to the Icom 756 Pro-III, I'd grab it in a heartbeat.
Otherwise, the antenna and feedline will be optimized as time permits.

73.

Russ
W6OHM

2-meter Preamp?
 

"998cc" wrote in message
...

Stack another yagi so you can reply to what you hear.


If he has room for it, this may very well be the best way to go. Gets
away from finding an amp that can take 500W on transmit, and does away
with complicated sequencing, which, if not done right could blow the amp
if you accidentally use VOX. For starters, replacing the 706 will
probably result in the best fun factor.

Tam/WB2TT

Tam, that would be great, but I live in a community with CC&R's and
antenna restrictions. I was barely able to get permission for my single
yagi by using 911 and the Loma Prieta earthquake as bases for arguments.
I really don't want to push the issue too hard. I do agree that looking
into a better radio is probably the first step. If they made a VHF/UHF
radio with similar features to the Icom 756 Pro-III, I'd grab it in a
heartbeat. Otherwise, the antenna and feedline will be optimized as time
permits.

73.

Russ
W6OHM

A few years ago I bought an FT847 as a backup/VHF/UHF rig. Wish I had spent
a few hundred more for a TS2000. A friend has one, and it is very nice if
you don't mind the art deco styling.

Tam/WB2TT

2-meter Preamp?
 

"Tam/WB2TT" wrote in
:

A few years ago I bought an FT847 as a backup/VHF/UHF rig. Wish I had
spent a few hundred more for a TS2000. A friend has one, and it is
very nice if you don't mind the art deco styling.

Talking of 144Mhz (the context of the original posting)...

Competition means that all these guys claim similar SSB telephony
sensitivity (measured in a shielded room) which corresponds to an
equivalent noise temperature of about 600K.

A key issue is that on a real antenna, this 600K could easily be 6000K
due to noise created by IMD in the receiver, and that doesn't show up on
the spec sheets, you can only assess that in situ, and it varies from
receiver to receiver and antenna to antenna. (The same issue exists with
any preamp or LNA.)

Carrying on with the (slightly unrealistic) best case of a 600K receiver,
used without a preamp and with say 1dB of line loss, your receiver
equivalent noise temperature is nudging 700K which is probably adequate
unless you are in the quietest of locations.

What 'works' for someone else isn't guaranteed to 'work' the same for
everyone.

An interesting illustration was the case of one of my VHF neighbours who
had a narrow filter (of the type used in two way radio duplexors)
installed between his preamp and transceiver. I asked why that
configuration and the answer was to minimise the loss in front of the
preamp (0.5dB of filter loss would add 35K to the system noise
temperature). On my suggestion, he moved it in front of the preamp and
compared the difference in S/N on a beacon and it was noticeably better
in front of the preamp, so despite the additional 35K, it had reduced
preamp IMD noise by more than that amount.

You don't make contacts in a shielded room, don't depend entirely on
shielded room perspectives for station design.

Owen