At 09:25 PM 9/17/2007, you wrote:

Welcome to the wonderful world of mast-mounted preamps! 90% of the people who get involved with satellites (INCLUDING myself) think they don't *need* a preamp. After doing all you can (better antenna, lower loss feedline, etc) to get your receive setup maxed out, you finally decide to "just try one; I can always sell it on eBay", and are usually amazed at the improvement it gives you. The _first_ thing I suggest to newcomers is to buy a good preamp. Sadly, most are like I was, and stumble around for weeks or months worrying about other things before finally buying one. Congrats, and enjoy your preamp! 73, Jim KQ6EA

Right on the nose, Jim, and they don't have to be expensive either,....the ones I use are from HAMTRONICS (assume they are still in business). they are at least 20 years old, built from a kit, and mounted in a wx proof box at the antenna, still functioning 100% and as I remember about 18 bucks at the time. They outdid others on a side by side coax switched test, and needless to say the owner of the "big time charlie"was not too happy!! Hamtronics has pre-built for a few bucks more, or did at that time...Use them, and hang just about any kind of antenna on for what we have flying now....One made from coat hangers would work just fine...And I've said this before.....low loss coax, and prime connectors properly attached.

I see the "antenna discussers" on here having the time of their life, and more power to them, probably on of the most fun parts of ham radio for some of us, but don't forget to include and calculate LOSES in the entire system. Your most magic antenna can go down the tubes with them.

73, Dave wb6llo@amsat.org Disagree: I learn....

Pulling for P3E...

I've never used hamtronics *preamps*, but I've built some of their other stuff. It seemed to me that the manuals assumed you'd built things before (not a problem for me), and they weren't real "user friendly" like Heathkit or Elecraft. The pines shouldn't be too much problem at VHF/UHF, but will kill you on 2.4GHz. 73, Jim

--- Bryant bryantcw@cox.net wrote:

Dave and the BB-

The thread on antenna preamps has been very interesting and helpful to me as I'm in the final stages of] putting my satellite station on the air- [determining where to mount the antennas at the moment]. I checked your reference to Hamtronics and they are still in business and do offer a wide range of inexpensive preamps. See http://www.hamtronics.com/lnk.htm.

I wonder if anyone else has had any experience with these preamps and, if so. what were your conclusions?

Also, does anyone know how much affect pine trees have on ham satellite communications? There are two tall ones within 30 meters of where I'm considering mounting my antennas.

Thanks for all the good ideas that the BB members have shared over the years.

Bryant, W2RGG/6, AMSAT member # 25030

Original Message ----- From: Dave Guimont To: Jim Jerzycke Cc: amsat-bb@amsat.org Sent: Monday, September 17, 2007 10:53 PM Subject: [amsat-bb] Re: New Preamp

At 09:25 PM 9/17/2007, you wrote:

...

Welcome to the wonderful world of mast-mounted preamps! 90% of the people who get involved with satellites (INCLUDING myself) think they don't

*need*

...

a preamp. After doing all you can (better

antenna,

...

lower loss feedline, etc) to get your receive

setup

...

maxed out, you finally decide to "just try one; I

can

...

always sell it on eBay", and are usually amazed

at the

...

improvement it gives you. The _first_ thing I suggest to newcomers is to

buy a

...

good preamp. Sadly, most are like I was, and

stumble

...

around for weeks or months worrying about other

things

...

before finally buying one. Congrats, and enjoy your preamp! 73, Jim KQ6EA

Right on the nose, Jim, and they don't have to be expensive either,....the ones I use are from HAMTRONICS (assume they are still in business). they are at least 20 years old, built from a kit, and mounted in a wx proof box at the antenna, still functioning 100% and as I remember about 18 bucks at the time. They outdid others on a side by side coax switched test, and needless to say the owner of the "big time charlie"was not too happy!! Hamtronics has pre-built for a few bucks more, or did at that time...Use them, and hang just about any kind of antenna on for what we have flying now....One made from coat hangers would work just fine...And I've said this before.....low loss coax, and prime connectors properly attached.

I see the "antenna discussers" on here having the time of their life, and more power to them, probably on of the most fun parts of ham radio for some of us, but don't forget to include and calculate LOSES in the entire system. Your most magic antenna can go down the tubes with them.

          73, Dave wb6llo@amsat.org
                  Disagree: I learn....

             Pulling for P3E... 

---

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--- scott wilson s.wilson@yahoo.com wrote:

...

Hamtronics and they are still in business and do offer a wide range of inexpensive preamps. See http://www.hamtronics.com/lnk.htm.

I have a couple of concerns about those preamps. They are probably fine for portable/HT operation, but they may not be up to a permanent base station application. The first concern would be with weather. If you look at the SSB preamps, you'll see that they are enclosed in a weatherproof case with the connectors facing downward, and are inside of an RF sheilded case inside of that.

Second would be the power handling capabilities.

In fact, they have no power handling capabilities, as they don't have a relay. For me, this ruled out both DEM and Hamtronics, as I decided that I simply didn't want to have to put a relay assembly together that would reliably deal with 100 watts at 432. Buying one would have been out of the question, unless I got lucky on ebay. The end result would have been more versatile, but probably not less expensive.

Bob

Indeed....a preamp can be a good thing. I own one myself. But, in my current location, a preamp is causing too much compression and I end up with lots of unwanted noise and other products that make it worse. It is true that I get a good amplification of the received signal, but the total, overall result is worse. Sigh.....the term location, location, location is so true. I overlook the city of Frankfurt, Germany and there is simply too much high power RF that gets sucked into my amp, along with the signals I do want.

I have a WACCOM cavity filter for both VHF and UHF that I'd like to use at the mast head, but they are too big to get up there (and they are not weather proof). Oh, and they are only a couple dozen KHz wide, which makes tuning to a different frequency a bummer.

My moral, if it works, by all means do it. But from my experience, attenuation is just as valuable as amplification. It all depends on your individual situation. Maximum gain doesn't always mean maximum useable signal. Maximum total system noise figure can be a bit daunting to achieve. I sometimes need to keep reminding myself that this is only a hobby and I am getting way too serious!!

Gary, N7BRJ/DA1BRJ

-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Jim Jerzycke Sent: Tuesday, September 18, 2007 6:26 AM To: Bob Stewart; Amsat-BB Subject: [amsat-bb] Re: New Preamp

Welcome to the wonderful world of mast-mounted preamps! 90% of the people who get involved with satellites (INCLUDING myself) think they don't *need* a preamp. After doing all you can (better antenna, lower loss feedline, etc) to get your receive setup maxed out, you finally decide to "just try one; I can always sell it on eBay", and are usually amazed at the improvement it gives you. The _first_ thing I suggest to newcomers is to buy a good preamp. Sadly, most are like I was, and stumble around for weeks or months worrying about other things before finally buying one. Congrats, and enjoy your preamp! 73, Jim KQ6EA

--- Bob Stewart bob@evoria.net wrote:

My new 70cm preamp came in today! I got the ARR mast-mount version. I wasn't sure I'd hear any improvement, but it's very noticeable. I was able to hear QSOs on SO-50 down to about 15 degrees tonight, whereas before, 20 was really stretching. I am using a turnstile in the attic with reflector elements at about 9.25" below the radiators. I can see that I'm eventually going to have to build more robust versions of my turnstiles and put them on top of the roof.

My power supply is a bit odd, so maybe someone will get a kick out of it. I have an Atlas 210X left over from years ago, and the PSU will power either of my bricks. The 210X slides into the PSU which an SO-239 on the back of it. In order to get the power up to the preamp, I added a fused switchbox and sent the power through that SO-239. This allowed me to just screw on a Radio Shack 50 ft length of RG-58 without having to cobble up a connector on the rig end.

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Domenico:

Greetings once again. You sent me a note some time ago that helped to amplify my current belief concerning SNR.

I am willing to bet two things.

First, it is difficult (not impossible, just difficult) to obtain a better front end noise figure than what the original receiver manufacturer has created. Almost certainly the addition of an outboard amp will add more noise. And this is not always a bad thing. A preamp can be a great addition despite the addition of more noise. But then you get into a curve of cost vs true value of gain. Is it worth it? Maybe so.

Second, it is very unlikely that maximum signal strength will be at the same point as maximum signal to noise ratio (SNR). Again, maybe this is not a bad thing in any one individual case. Almost certainly the best SNR will be at a point of gain somewhat less than maximum.

I work with receivers and preamps that cost dozens of thousands of dollars. Cost and receive noise figure is almost a logarithmic curve. And it seems that only with the very best front ends are SNR and gain at the same point.

Once you get the best receiver, coax and antenna you can afford, that is all you can do....which seems like a dumb and obvious thing to say. Beyond that, true magic is hard to come by. And I am not knocking the preamp. Again, I own and use them all the time.

73!

Gary, N7BRJ/DA1BRJ

-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of i8cvs Sent: Tuesday, September 18, 2007 6:17 PM To: Gary Memory; 'Jim Jerzycke'; 'Bob Stewart'; 'Amsat-BB' Subject: [amsat-bb] Re: New Preamp

----- Original Message ----- From: "Gary Memory" gmemory@tks-net.com To: "'Jim Jerzycke'" kq6ea@pacbell.net; "'Bob Stewart'" bob@evoria.net; "'Amsat-BB'" amsat-bb@amsat.org Sent: Tuesday, September 18, 2007 8:22 AM Subject: [amsat-bb] Re: New Preamp

I have a WACCOM cavity filter for both VHF and UHF that I'd like to use at the mast head, but they are too big to get up there (and they are not weather proof). Oh, and they are only a couple dozen KHz wide, which

makes

tuning to a different frequency a bummer.

Gary, N7BRJ/DA1BRJ

Hi Gary, N7BRJ/DA1BRJ

For my similar situation in the bay of Naples wich is full of RF pollution I use the following K3PGP home brewed filter at the mast head in front to the low noise 70 cm preamplifier and a 70 cm cavity filter in the shack in front of my 70 cm downconverter or 70 cm receiver.

Please read the article.

http://www.k3pgp.org/432filter.htm

Similarly for 2 meters I have scaled the dimentions of the above filter wich is antenna mounted in front of the 2 meters preamplifier and a 2 meters cavity filter of the type used for the FM repeaters is in the shack in front of my 2 meters downconverter or receiver.

I remember receiving OSCAR-13 on 145.950 MHz I was able to locally translate the satellite at 145.250 MHz FM transmitting with 2.5 watt using another antenna to show locally the satellite performance without desensing the bird.

This setup is obviously permanently tuned and devoted for receiving the 70 cm and 2 meters satellite bands and it works.

73" de

i8CVS Domenico

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--- Bob Stewart bob@evoria.net wrote:

--- Gary Memory gmemory@tks-net.com wrote:

...

First, it is difficult (not impossible, just difficult) to obtain a better front end noise figure than what the original receiver manufacturer has created.

Is this for the latest whiz-bang radio, or the ~8db NF FT-726R that I have?

I disagree with this comparison of quality mast-mounted, band specific preamps to built-in wideband transceiver pres. I can't imagine that the DC-daylight preamp in my $1000 transceiver could have been engineered to the same performance specs on 70cm as a $500 70cm specific preamp with helical filters. Not that $$$ spent is all gained in return, but it gives an idea about the potential budget that can be allocated to the various materials used in construction.

I was discouraged by the preamp nay-sayers, but for satellite work, I think understanding what makes a preamp useful is the key to deciding if you want one. In my case, it was well worth it.

Regards,

Scott NW2S

----- Original Message ----- From: "Gary Memory" gmemory@tks-net.com To: "'i8cvs'" domenico.i8cvs@tin.it; "'Amsat-BB'" amsat-bb@amsat.org Sent: Tuesday, September 18, 2007 8:26 PM Subject: RE: [amsat-bb] Re: New Preamp

Domenico:

Greetings once again. You sent me a note some time ago that helped to amplify my current belief concerning SNR.

I am willing to bet two things.

First, it is difficult (not impossible, just difficult) to obtain a better front end noise figure than what the original receiver manufacturer has created.

Hi Gary, N7BRJ/DA1BRJ

This is why we use a low noise preamplifiers antenna mounted. Make an example: The noise figure of a commercial receiver like a TS-736 is about NF=6.5 dB corresponding to an equivalent noise temperature T1= 1005 kelvin If you add a low noise preamplifier antenna mounted with a NF= 0.5 dB and if the overall noise figure of the system is degradated to NF= 0.7 dB corresponding to T2 = 51 kelvin then using the same antenna the improvement of S/N using the above preamplifier is: 10 log (1005/51) = 13 dB 10

Almost certainly the addition of an outboard amp will add more

noise. And this is not always a bad thing.

In the above example the more noise that you see on your S-meter is only apparent because the gain of the system probably is too great but you can reduce the noise reading of the S-meter without reducing the S/N ratio adding an attenuator and this is particularly easy to do if you use a preamplifier + downconverter + attenuator + IF receiver

A preamp can be a great addition despite the addition of more noise.

If you get more noise degrading the S/N it meens only that the NF of your preamplifier is greater then the NF of your receiver or its gain is too low.

But then you get into a curve of cost vs true value of gain. Is it worth it? Maybe so.

Adding a low noise preamplifier with the capability of improving the S/N ratio is always wortwhile.

Second, it is very unlikely that maximum signal strength will be at the same point as maximum signal to noise ratio (SNR).

The best noise figure NF of a preamplifier cannot correspond to the maximum gain as the S-parameters of a device for the lowest NF are showing.

Again, maybe this is not a bad thing in any one individual case. Almost certainly the best SNR will be at a point of gain somewhat less than maximum.

The important of the point is that even if the lowest noise factor F1 do not correspond to the maximum gain the gain G1 obtained from it be sufficient to get a satisfactory overall noise factor Ft of the system as the formula for more stages in series is showing:

F2-1 F3-1 Ft = F1 + --------+ --------- + .................. G1 G1xG2

I work with receivers and preamps that cost dozens of thousands of dollars. Cost and receive noise figure is almost a logarithmic curve. And it seems that only with the very best front ends are SNR and gain at the same point.

This is not strictly mandatory for as Radio Amateurs.

Once you get the best receiver, coax and antenna you can afford, that is all you can do....which seems like a dumb and obvious thing to say. Beyond that, true magic is hard to come by. And I am not knocking the preamp. Again, I own and use them all the time.

Once I get the best receiver and the best antenna I must reduce the thermal noise of the coax cable wich noise factor is F1 in the above formula so that to improve the S/N ratio I have to add a low noise preamplifier in F1 with the maximum possible gain in G1

73!

Gary, N7BRJ/DA1BRJ

Best 73" de

i8CVS Domenico

Thanks Domenico,

I was about to insert my comments to Gary.

I would challenge his belief that manufacturers achieve better NF, as the evidence shows the contrary. If you can show me a commercial radio with 0.5 dBNF on the 150-MHz band, then I would love to know it. Almost all commercial two-way radios have a sensitivity of about 0.15 to 0.25 uV at 15-KHz BW. This will result in about MDS of > -124 dBm and a NF well over 3-dB. Commercial equipment is designed for immunity from high RF/noise urban environments and that trades off noise figure in the process (commercial radios are designed for strong signals - hams* are the crazy weak-signal nuts!) *and a few weird radio astronomers, NASA engineers, ....

My 2m eme station has a sensitivity of -147.5 dBm with 2.2 KHz SSB BW; that is a receiver temp= 58K or NF=0.79 dB. This is assuming 0.5 dB loss ahead of the preamp. A good ham radio VHF satellite receiver will be about 100K or NF=1.2 dB with a sensitivity of -145 dBm at 2.2 KHz SSB BW.

Now if you add sky noise, industrial noise, and antenna noise, the system sensitivity (Te) will suffer: Te = Tr+Tsky+Tant+Tindustrial e.g. using Tsky = 210K, Tant = 45K (very good low sidelobe eme class antenna), and no man-made noise (my situation): Te = 313K, and Pn = -140 dBm (note no antenna gain is included in this number) so my environment cost me about 7.5 dB in sensitivity. Obviously if you have several hundred degrees of industrial noise then things do get worse which will minimize the advantage of the low NF preamp. Here the use of well engineered filters may help. Preamps with better strong signal characteristics (though a bit higher NF) may also help.

Tradeoffs of NF vs gain are made in low noise amplifiers (preamps) usually in favor of low NF. As long as there is sufficient gain to overcome the higher NF of the following receiver the overall system will benefit. Usually this means a min of about 16 dB gain. This will lower the noise contribution of the following circuits by 1/40.

For the majority, a good low-noise preamp mounted at the antenna will result in significant increase in hearing ability. caveat emptor

73 Ed

At 12:33 PM 9/18/2007, i8cvs wrote:

----- Original Message ----- From: "Gary Memory" gmemory@tks-net.com To: "'i8cvs'" domenico.i8cvs@tin.it; "'Amsat-BB'" amsat-bb@amsat.org Sent: Tuesday, September 18, 2007 8:26 PM Subject: RE: [amsat-bb] Re: New Preamp

...

Domenico:

Greetings once again. You sent me a note some time ago that helped to amplify my current belief concerning SNR.

I am willing to bet two things.

First, it is difficult (not impossible, just difficult) to obtain a better front end noise figure than what the original receiver manufacturer has created.

Hi Gary, N7BRJ/DA1BRJ

This is why we use a low noise preamplifiers antenna mounted. Make an example: The noise figure of a commercial receiver like a TS-736 is about NF=6.5 dB corresponding to an equivalent noise temperature T1= 1005 kelvin If you add a low noise preamplifier antenna mounted with a NF= 0.5 dB and if the overall noise figure of the system is degradated to NF= 0.7 dB corresponding to T2 = 51 kelvin then using the same antenna the improvement of S/N using the above preamplifier is: 10 log (1005/51) = 13 dB 10

Almost certainly the addition of an outboard amp will add more

...

noise. And this is not always a bad thing.

In the above example the more noise that you see on your S-meter is only apparent because the gain of the system probably is too great but you can reduce the noise reading of the S-meter without reducing the S/N ratio adding an attenuator and this is particularly easy to do if you use a preamplifier + downconverter + attenuator + IF receiver

...

A preamp can be a great addition despite the addition of more noise.

If you get more noise degrading the S/N it meens only that the NF of your preamplifier is greater then the NF of your receiver or its gain is too low.

...

But then you get into a curve of cost vs true value of gain. Is it worth it? Maybe so.

Adding a low noise preamplifier with the capability of improving the S/N ratio is always wortwhile.

...

Second, it is very unlikely that maximum signal strength will be at the same point as maximum signal to noise ratio (SNR).

The best noise figure NF of a preamplifier cannot correspond to the maximum gain as the S-parameters of a device for the lowest NF are showing.

...

Again, maybe this is not a bad thing in any one individual case. Almost certainly the best SNR will be at a point of gain somewhat less than maximum.

The important of the point is that even if the lowest noise factor F1 do not correspond to the maximum gain the gain G1 obtained from it be sufficient to get a satisfactory overall noise factor Ft of the system as the formula for more stages in series is showing:

              F2-1       F3-1

Ft = F1 + --------+ --------- + .................. G1 G1xG2

...

I work with receivers and preamps that cost dozens of thousands of dollars. Cost and receive noise figure is almost a logarithmic curve. And it seems that only with the very best front ends are SNR and gain at the same point.

This is not strictly mandatory for as Radio Amateurs.

...

Once you get the best receiver, coax and antenna you can afford, that is all you can do....which seems like a dumb and obvious thing to say. Beyond that, true magic is hard to come by. And I am not knocking the preamp. Again, I own and use them all the time.

Once I get the best receiver and the best antenna I must reduce the thermal noise of the coax cable wich noise factor is F1 in the above formula so that to improve the S/N ratio I have to add a low noise preamplifier in F1 with the maximum possible gain in G1

...

73!

Gary, N7BRJ/DA1BRJ

Best 73" de

i8CVS Domenico

---

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73, Ed - KL7UW ====================================== BP40IQ 50-MHz - 10-GHz www.kl7uw.com 144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w DUBUS Magazine USA Rep dubususa@hotmail.com ======================================

----- Original Message ----- From: "Gary Memory" gmemory@tks-net.com To: "'Edward Cole'" kl7uw@acsalaska.net; "'i8cvs'" domenico.i8cvs@tin.it; "'Amsat-BB'" amsat-bb@amsat.org Sent: Wednesday, September 19, 2007 7:12 PM Subject: RE: [amsat-bb] Re: New Preamp

Adding a preamp in my case is a total disaster. I could probably put a diode in my coax line and then charge batteries with the resulting DC.

73!

Gary, N7BRJ/DA1BRJ

Hi Gary, N7BRJ/DA1BRJ

Your case is similar to my situation in the bay of Naples and our problem cannot be solved using commercially made GaAsFET preamplifiers because they have a very low 1 dB compression point and a very low IP3 intercept point.

Buy the way very rapid advances have been made in the last twenty years in the development of semiconductors.It seemed that at first the field effect transistor (FET) and then GaAsFET were getting more and more popular over bipolar transistor, especially with respect to the noise figure from VHF to UHF

However the modern bipolar transistor is still of importance in receive technology,especially since a well know type of "Noisless Feedback Circuit" developed by Dr. David Norton allow them to be made more linear and exhibits less noise than a FET and greater IP and dynamic range than a GaAsFET

Since desensitization and overload are becoming a serious problem particularly in 2 meters as more and more amateurs started using high power linears and large directive antennas, the Norton circuit seems to be a modern solid state solution to the designe goals in those case like our case when, for 2 meters satellite communications, an extremely low noise figure less than 1.5 dB is not strictly necessary but, a very high IP and compression performance may be more useful.

On today crowed 2 meters amateur band and the high incidence of very near kilowatt transmitters, strong signal performance (1 dB compression and IP3) in preamplifiers is usually much more important than sensitivity.

For the above mentione reason I have homebrewed a Norton preamplifier for 2 meters using a BFG-195 + BFG-134 that exibit the following measured performance: Noise Figure NF= 1.4 dB Gain G= 20.5 dB 1 dB compression point = + 28 dBm = 631 mW of output power and since +28 dBm - 20.5 dB = +7.5 dBm = 5.6 mW it means that 5.6 mW applied to the input of this preamplifier are necessary to compress the gain of only 1 dB Third Order Intercept Point IP3 = +22.5 dBm input

For 70 cm I have homebrewed a Norton preamplifier with a AT-42085 + AT42085 that exibit the following measured performance: Noise Figure NF= 1.3 dB Gain G=19 dB 1 dB compression point = + 26 dBm output power IP3 = +22 dBm input

For those who are interested to duplicate the above Norton preamplifiers as well some special type of power GaAsFET preamplifiers having low NF with high intercept point and dinamic range here are some useful references:

1) High Dinamic Range Transistor Amplifier using Lossless Feedback by David Norton Microwave Journal May 1976

2) A new type of Preamplifier for 145 and 435 MHz Receivers by M. Martin DJ7VY VHF Communications 1/1978

3) High IP - LNA for 432 MHz by R. Bertelsmeier DJ9BV DUBUS N° 2 /1992

4) Proceedings of the 24 th Conference of the Central State VHF Society ARRL Catalog Nr 3266 "Power GaAsFET Preamps, by Ken Britain WA5VJB pages 6-8

5) Proceedings of the 25 th Conference of the Central States VHF Society, ARRL Catalog Nr 3614 144 MHz GaAsFET Preamplifier by Tommy Anderson WD5AGO, page 35-36

NOTE: Only a simple noise generator made with a diode and described in any Handbook is necessary to adjust the above preamplifiers for the lowest NF

If the ENR of the noise generator is not calibrated the value of the obtained noise figure will be unknow but it will be the minimum possible obtainable for that device in that preamplifier.

73" de

i8CVS Domenico

----- Original Message ----- From: "Edward Cole" kl7uw@acsalaska.net To: amsat-bb@amsat.org Sent: Thursday, September 20, 2007 8:44 AM Subject: [amsat-bb] Re: New Preamp

Wonder what your opinion is of the mfg-1801 low-power transmitting GasFet? This is what I am using for eme with fabulous results.

Although I stated earlier having no RF interference that is probably not completely accurate. But it seems this preamp is very durable and not particularly susceptible to RF overload. It was measured at 0.15 dB NF with 16.8 dB gain at CSVHFS in 1999.

With four 10-element yagis I am talking with 2m mobile and even a couple HT's over 70-miles from me. That is on FM simplex.

73, Ed - KL7UW

Hi Ed, KL7UW

Following the designe of WA5VJB and WD5AGO described in references 1 and 2 of my previous message and the EME newsletter december 1990 from K2UYH I obtained a few power GaAsFET MGF-1801 and MGF-2116 from KY7B and at 145 MHz preamplifiers I got NF=0.22 dB with G= 25 dB and input IP3= + 1 dBm as measured during official measurements at the eighth Experimentation Symposium Orvieto Italy

My three prototype preamplifiers are fully described in italian with all mechanical drawings in Radio Rivista 1/1994 page 20 to 25 , Radio Rivista 9/1994 page 20 to 24 and Radio Rivista 1/1995 page 36 to 40

Extremely low noise figure, very high gain and high level third-order intercept point can be all obtained at 144 MHz using GaAsFET's designed for power amplifiers at 10 GHz

This very interesting and unexpected effect was at first casually discovered by amateurs in 1990 when WB5GKL needed a high dinamic range preamplifier for a commercial application near 150 Mhz and he hoped that power FET would handle the strong local signals.

Using 10 GHz power FET's WB5GKL obtained at VHF kind of like building an HF 160 meters receiver front-end using a 4CX250 and the same results were obtained and described in the already mentioned references 1 and 2 by WA5VJB and WD5AGO respectively.

Probably the larger gate of power FET's devices for 10 GHz just work better at VHF because the power FET's have 3000 times as much gate area than the small signal FET's and so a very, very low internally generated noise, but what's really happening must be still carefully investigated because power FET's got poor noise figure at 432 MHz and it looks like the present FET's designs are going to be usefull for just 144 and 220 MHz

I am very happy with the performance of my above 145 MHz preamplifiers but the only problem is that they are a very long coaxial resonant line about 45 cm long so that for real life satellite work at 145 MHz I prefere to use a Norton type preamplifier which is smaller and lightweight.

Best 73" de

i8CVS Domenico

Gary Memory wrote:

The only thing I would add to your comments is that to amplify signals before an existing front, with a given antenna and feed line, can't help but have a negative impact somewhere else. Maybe that negative is no big deal.

I haven't jumped into this conversation, but really the issue is that a lot of hams seem to want to "do it once, and never change it" or they want someone ELSE to do the experimentation, real measurements, and WORK for them. They want "Plug and Play"... instant gratification.

This leads to endless online debates by those who WON'T go DO, and keeps the rest of us who HAVE played with pre-amps and the resulting real-world complexity from even commenting.

You might see a "XYZ setup works great for me, but..." from a few people, but not many -- when these threads come up.

The reality is, designing an RF *SYSTEM* for a particular location, site noise floor, receiver, transmitter power level, etc... and making it perform to the absolute best that it theoretically can -- is hard work, that many simply aren't willing to do.

RF Engineers/Professional RF Technicians get paid big bucks to do this level of work in non-Amateur systems, and many are also Amateurs, so they benefit from their knowledge and experience, and know WHICH trade-offs they'd like to make... since every particular setup of any complete RF system, always has a few.

The less stages of anything before demodulation, the better chances you have at a super receive chain. And with another stage of amplification or a preamp, certainly you just have to hope that no strong signal will come up anywhere nearby in frequency or distance to what your receiver is set to. What about dynamic range....wouldn't a preamp toss that into the toilet? Again, maybe it is no big deal to the end you are after.

Yep, you just HAVE to measure, make a theory, test that theory via experimentation, and then wash-rinse-repeat until you're either happy with the result, or you've run out of ideas.

My advice about advice is this: Listen to others, study and learn about it yourself, and then go do whatever you want. In the world of radio, no amount of paperwork, planning and talking beats trying it to see if it works. I have several preamps of all kinds and I use them whenever possible, but I realize their limitations.

Depends on your knowledge level. Those who've "been there done that" can always benefit from running the numbers ahead of time and planning, while taking their experience into account.

Some *might* even share what "works for them" as some do, but your advice is dead-on for newbies. Go try something, learn how to measure it properly, learn the math, and get hard numbers to see how YOUR station works out.

(And frankly, since a lot of us are "just Amateurs" one of the distinct reasons that some of us don't pipe up and say anything is because we don't feel comfortable with the math, or whatever reason... we're not "classically trained" as they say, and people that are sometimes accidentally come across as harsh when they correct mistakes in online forums... I say accidental, because I've done it on other topics, and didn't know I hurt someone's feelings.)

Finally, to those who sent some perty nasty comments via private mail re this thread...Gee...I am sorry. Really I am. I had no idea my comments were so flammable. I'm betting that stealing your wife or girlfriend (boyfriend?) would not be as traumatic? What can I say? I didn't mean to cause trouble. To me, this is a hobby. A fun pastime. I promise, I won't make comments again. I rarely do make comments on this board...because every time I do, there are those who take it so seriously. Geezzooo!

This is what really made me want to comment. Ignore the cowards behind their keyboards who can't be civil. So many people do this, that there are psychological studies about how people's personalities change when they feel "safe" from retribution behind a keyboard and a screen. In any "normal" multiple-person conversation they'd either be shunned or someone would hit them upside the head with a clue-bat. But anyway, it really isn't worth worrying about them.

Let 'em be unhappy, that's their choice to be sour/mean/whatever, and has no impact on you, if you don't allow it to. It's just an extension of their own reality, and once you realize that, you realize that some people live in very drab/angry/sad worlds of their own creation. Not much fun.

Back to the pre-amps and duplex operation, for those that have never worked on them, remember that people building repeaters do exactly that... all the time. And most add pre-amps in some fashion or another to their repeater systems (as someone pointed out, many commercial FM rigs only do anywhere from .2uV - .3uV sensitivity for 12dB SINAD (since we are talking about FM at the moment, you gotta have that 12dB SINAD reference point), and repeater owners/operators everywhere want better receivers than THAT!

There's tons of information on the Net and in books about how to duplex a repeater system, while maintaining high receiver sensitivity, and pushing lots of power out the TX side... which are all similar goals to what Satellite ops are trying to do, perhaps.

I only mention this as a reminder to those that hadn't thought about it, that sites like http://www.repeater-builder.com and others have lots of "basic starting point" information about that type of setup and how to measure it... just change "repeater transmitter" to "uplink", and "repeater receiver" to "downlink" in your mind and keep in mind that you're often not on the same BAND in satellite operations for those two frequencies, so duplexer/filter stuff won't be "quite right"...

But, it gives your brain a frame of reference to get your head around the measurements the super-smart folks are doing on their RF systems.

And most of all, folks gotta remember to HAVE FUN with all this stuff... it's not a job, it's a hobby... And it's not even more important than the family dog, when the dog is sick and needs to go to the vet.

Nate WY0X