Low Power 70 cm linear

[K9STH]

First of all, google is NOT my friend, at least on this! I went through over 300 "hits" on google and did not come up with anything! Now I know that "somewhere" in my hundreds of amateur radio magazines that I have the information. But, taking hours to look is a last resort!

What I need is an article that includes the board layout for a solid-state linear amplifier stage that can take between 0.5 and 1 watt input and put out at least 10 watts. The reason for this is that I have made a trade for a 432 MHz transverter that is missing the final amplifier board. The power output right now is just under 1 watt and I really need to get the power up to at least 10 watts to drive my tube-type amplifier (uses a single 4CX250B in a grid driven configuration). The amplifier is from an old Motorola "B" 100 watt output FM unit that puts out a comfortable 150 watts at 432 MHz. I do need to change the bias on the amplifier so that it will operate as a linear amplifier rather than a Class "C" as right now. But that will come after getting the power "up" on the transverter.

The transverter will be in my hands by this time next week and I want to get a "head start". I have plenty of parts including power transistors that are capable of considerably more power than 10 watts. It is just that I haven't been able to locate an article with the desired information.

When everything is completed I plan to get my 27 element simulated plane reflector yagi at about 60 feet above ground fed by 7/8th inch Heliax. The antenna was made by J-Beam Ltd. in the United Kingdom. Since I am 1/2 block from the highest point in the city I expect to be able to "get out" fairly well.

Glen, K9STH

[VK2TIL]

Not quite what you asked-for but MiniKits (Mark VK5EME) has a Mitsubishi-module kit that might do;

http://www.minikits.com.au/kits2.html

Scroll down to the 30W/430MHz kit.

A$80.50 looks like a good deal; our dollar has fallen recently.

The Mitsubishi data sheets for their modules (eg RA30H4047M) have enough information for "rolling your own" if you want to do that.

[K9STH]

The Mitsubishi RA30H4047M is available here in the United States for $39.95 US, at least from r.f. Parts. According to http://www.x-rates.com/calculator.html the amount that he is charging for the module is $44.94 US which is a $5 US difference plus shipping.

The kit without the module is $20.83 US and the entire kit is $65.77 US. The difference between getting the entire kit from Australia and getting the kit less the module from Australia and the module here in the United States would be right at $5 plus the difference in shipping.

I will keep this in mind. However, I have quite a few r.f. transistors and other parts on hand that I definitely would rather use! If I can find a schematic and board layout I can make the assembly at no "out of pocket" cost which, of course, is VERY attractive to me!

I believe that I also have some of the modules around. However, I need to see if these are actually linear or are class "C" since they would normally be used in FM equipment.

Glen, K9STH

[VK2TIL]

Some of the old Motorola appnotes might help, eg;

http://bogor.net/idkf/idkf-1/community-broadcasting/datasheet/application-note/AN548A.pdf

The Motorola (and many other) appnotes of that era were great practical documents thanks to engineers (such as Helge Granberg) who could communicate!!

[W9GB]

It is too bad that Communication Concepts does not offer a UHF version of their MODEL 335A (35 WATT VHF AMPLIFIER)
http://www.communication-concepts.com/335a.htm

w9gb

[K9STH]

I found the circuit that I was looking for! It is in the 1985 edition of the ARRL Handbook. Has a 10 dB gain (which is what I am looking for) and relatively few parts. However, there is one major thing with the text. Therein it is stated that the template for the circuit board is in the back of the handbook along with other templates. Unfortunately, there are quite a number of templates but the one for the amplifier is not there. In fact, it is not even listed in the table of contents for the template section.

Fortunately, there is a full size drawing showing the parts layout. So, I scanned that and then used my graphics program to take out the parts and then make the necessary dark template to make the circuit board.

Then, on the next page is an article on building a single 4CX250B amplifier which just happens to be very close in design to the Motorola "B" amplifier that I have been using for years on CW. The few circuit changes that have to be made to change the class "C" amplifier to a linear amplifier are quite apparent and that will save me some time in redesigning my 432 MHz amplifier. The design says full output (about 300 watts peak) with less than 10 watts drive. Now I have been getting 150 watts output CW without any problem and I will probably not run much more output on SSB just to "save" the tube.

I knew that I had the information "somewhere"! The circuit is not in any of my earlier Handbooks and not in any of my later Handbooks! Now I do not have every Handbook from that era but I do have a "fair" number of them. Frankly, I just "lucked up" when looking for the article because the 1985 edition was the 2nd one that I checked. I did check a couple before and after just to see if the article was in them and it was not!

Now I have to "dig out" some double sided board and get to work!

Glen, K9STH

[KA5LQJ]

Glen, All,

With some Part 90 - Public Safety agencies going to 700 & 800 mHz, wouldn't those units be coming up as surplus? I'm not sure what the comm shops do with them. I think they either scrap them or sent them back to Rotomoola, :rolleyes: :eek:

Seems a shame to scrap them. I don't know why some enterprising radio tech couldn't purchase them at a low cost, since they're being scrapped and convert them to 440-449 mHz use.

There's NOT a lot of 444 "traffic" here in Shreveport, LA. But, I imagine there would be if some of the guys could get these mobile units.

I'd love to have a hi-powered Lo-band, VHF, & UHF FM bases. You know, the ones in the TALL rack cabinets and yes, I have room for them. Then, the Icom 706 MkII-G would be used strictly for HF. ;) I love those old, Motorolas with the old desk mics. We had an old, 75 watter base station when I worked at Western Electric that I used to dispatch low-rise and fork trucks around the plant. When the company decided to get rid of the truck radios and base station, they took them out back on the "scrap dock" and beat them to smittereeen's with 16# sledge hammers.:( :confused: :mad:

Good luck with your project.

Respectfully,
73,

Don/KA5LQJ
Grid Square: EM-32

[K9STH]

There are 2 problems with using a commercial FM amplifier. The first is that the vast majority of them are for class "C" operation which is not linear. They are the most efficient for FM and CW but will not work at all for SSB. I have all sorts of class "C" amplifiers that would work fine if I were wanting to use them on FM. In fact, I have probably about 20 complete FM units around.

The second problem is that I am needing the amplifier for 432 MHz and not 440 MHz to 450 MHz and most of the commercial amplifiers are fixed tuned and will not usually make it down to 432 MHz without modification. Even those that are tunable are hard pressed to make it down to 432 MHz.

As I stated in my original request I have obtained a Microwave Module 432/28 transverter that has had the 10 watt amplifier removed. Since I now have it actually in my hands I find that it only puts out around 300 mW and therefore definitely needs an amplifier, maybe even a 2-stage.

Glen, K9STH

[AC0FP]

There are 2 problems with using a commercial FM amplifier. The first is that the vast majority of them are for class "C" operation which is not linear. They are the most efficient for FM and CW but will not work at all for SSB. I have all sorts of class "C" amplifiers that would work fine if I were wanting to use them on FM. In fact, I have probably about 20 complete FM units around.

The second problem is that I am needing the amplifier for 432 MHz and not 440 MHz to 450 MHz and most of the commercial amplifiers are fixed tuned and will not usually make it down to 432 MHz without modification. Even those that are tunable are hard pressed to make it down to 432 MHz.

As I stated in my original request I have obtained a Microwave Module 432/28 transverter that has had the 10 watt amplifier removed. Since I now have it actually in my hands I find that it only puts out around 300 mW and therefore definitely needs an amplifier, maybe even a 2-stage.

Glen, K9STH

Your going to have problems finding a linear in the 432 Mhz range, but you already know that. I remember seeing an article using a Motorola power module to make a "class C linear" for amateur TV sometime back. :D:D

73,

Frank

[K9STH]

I have found a couple of other articles that involve solid-state linears for 432 MHz SSB. One of them is pretty close to an amplifier that I have which comes from a Standard C766 commercial 450 MHz two-way transceiver. That amplifier is rated at 35 watts continuous FM output and has about 1/2 watt input. There are 3 transistors involved (a pre-driver, a driver, and a final amplifier). The transistors start with a 2SC2379, then an MRF-641, and the final is an MRF-646. It appears that the main thing I am going to have to do is to add a turn, or so, on the tuned circuits and to change a couple of bias resistors. Also, I need to remove the bandpass filter which pretty much covers the 450 MHz to 470 MHz range and attenuates frequencies above and below that range. That is a very simple movement of a wire.

In addition, the amplifier has a PIN diode type of antenna changeover which makes it easier on me because to run at least 35 watts peak output I would not have to have a separate antenna relay. There is a PIN diode antenna changeover in the transverter that will have to be bypassed and the one in the amplifier used instead. But, this will be an easy modification. When I add my 4CX250B amplifier I will have to come up with an outboard changeover relay. But, all that would involve is moving the cable to an added BNC connector on the transverter to the antenna relay.

To prevent overload and possible damage to the receiver "front end" I will use the same circuit as I used to use with my 432 MHz converter and the amplifier when I was running CW. That is I ground the lead to the converter antenna when in transmit before it gets to the changeover relay. This keeps the signal from getting back into the front end.

Also, I was going to use my Heath SB-301 / SB-401 combination that I run into my 2-meter transverter. However, my Hallicrafters HA-2 transverter can take the full output power of the SB-401 without any problems. Unfortunately, the 432 transverter requires a maximum of 1/2 watt at 28 MHz. I had considered putting the modifications that are used with the Heath SB-500 2-meter transverter but the transmitter still puts out over 5 watts and that would require an attenuator as well as considerable work to the SB-401. Therefore, I have decided to go ahead and use one of my Uniden HR-2510 transceivers as the i.f. It is possible to turn down the power to less than 5 watts output with an internal control. I still will have to make a simple attenuator for the transmit power but that is MUCH easier than modifying the SB-401 and then adding the switching to allow full power when I am not using the 432 MHz transverter. I have a control box that I made a number of years ago which allows me to use the Uniden with the Hallicrafters transverter. All that I will have to do to use it is to add the attenuator on the transmit side to the 432 MHz transverter.

The only "problem" is that the HR-2510 transmitter changes frequency in 100 Hz steps and is not continuous tuning like the SB-401. There is an RIT so that the receiver frequency can be varied without affecting the transmitted signal. Since I will not be using the 432 MHz station all that much using the HR-2510 as the i.f. will be OK. I used it with the 2-meter transverter and it worked fine. The only thing is that it takes quite a bit of "cranking" to tune very far looking for signals. On 432 MHz most of the activity, at least in this area, is within a very narrow range of frequencies.

The HR-2510 is an "all mode" unit in that it is capable of USB, LSB, AM, CW, and FM although I doubt very much that I will be running anything except USB and CW on 432 MHz.

Anyway, I am getting MUCH closer to having multi-mode signals on 432 MHz instead of just CW like I had before. Of course I was one of very few operators that have more power on 432 MHz than on 2-meters. My HA-2 puts out between 80 and 100 watts and my 432 MHz amplifier easily puts out 150 watts.

Glen, K9STH

[VK3FAIL]

i seen a few schematic drawings just trying to remember where
will edit my post when i can find them again

honestly loop yagi is the way to go they have better gain over majority of the trash thats made hence why majority of the atv op's in vk3 use them

[K9STH]

Is the antenna that you are referring to as a "loop yagi" the same antenna that was designed by Overbeck and called the quagi? Or, are you referring to an antenna with a folded dipole driven element rather than the usual dipole driven element?

My J-Beam Ltd 27 element 432 MHz yagi uses a folded dipole driven element (of course a 4:1 coaxial balun is required to use the antenna with coaxial cable) and has a simulated plane reflector which consists of 4 elements in the vertical plane. This gives the antenna between 2 and 3 dB additional forward gain.

A friend of mine made a number of 432 MHz quagi antennas for his friends. This person was a salesman for a fiberglass materials company and used fiberglass tubing for the booms instead of wood. Those antennas worked very well and a number of locals used them for mode B on the OSCAR VII satellite.

Glen, K9STH

[N0WVA]

Glen,

Not sure if this outfit can help you, but heres a link:

http://www.downeastmicrowave.com/Catalog.htm

[K9STH]

The main problem with this company is that my wife would go "through the ceiling" if I spent $160 for the amplifier kit!

I have been modifying an old amplifier section from a commercial two-way Standard C766 that requires less than 1/2 watt for 35 watts continuous output. The amplifier is Class "C" and has to be modified to be used as a linear.

Glen, K9STH

[W9PDS]

I just came across this post & have been interested in getting a small amp for my HT.

Looks like the AUS dollar has kept falling since this thread started. Price now is about $52 US for the entire kit + module.





The kit without the module is $20.83 US and the entire kit is $65.77 US.

[K9STH]

As of this morning the total price for the RA30H407M KIT2 (the kit plus the r.f. module) including shipping to the United States is $89.00 Au. The owner of the company, VK5EME, only wants PayPal and the exchange rate as of this morning was $89.00 Au equals $59.07 U.S. Shipping is by air mail. I have been in E-Mail communication with VK5EME and the $89.00 Au is what he quoted.

Therefore, I went ahead and ordered the complete kit.

I will have to pad down the 250 mW that my transverter puts out by 6 dB to get it down to the input power that the module requires for 30 watts output. Fortunately, a couple of 150 ohm resistors and a 39 ohm resistor in a Pi configuration will do that.

Glen, K9STH

[WY6K]

Glen,

I know you already went for that kit, but another solution to consider might be something like the Mirage D100. 200mw in minimum, with a gain of about 25. Maybe 6.25 watts is enough?

Here's one on ebay:
http://cgi.ebay.com/Mirage-D-100-TVN-420-450-Ham-Radio-Linear-Amplifier_W0QQitemZ180298136458QQcmdZViewItem?hash =item180298136458&_trkparms=39%3A1%7C66%3A2%7C65%3A1%7C240%3A1318&_trksid=p3286.c0.m14

[K9STH]

The price of the amplifier is already up to $46.00 with a shipping charge of $10.00 and there are over 6 days to go. That makes $56.00 and climbing. I would bet the final price is definitely more than the $59.07 that the kit cost including shipping and the kit should be here within a week.

30 watts is more than I need to drive my 4CX250B 432 MHz amplifier.

Glen, K9STH

[K9STH]

The 432 MHz amplifier kit came Monday afternoon and I built it right away. Then the "fun" began! The module requires between 50 mW and 100 mW of drive. Since my transverter was putting out 250 mW I put a 6 dB pad (3 resistors in a "Pi" configuration) to get the drive down to about 60 mW. However, when operating on SSB the module kept "taking off". It was fine on FM and AM but SSB was a completely different matter.

I added a 51 ohm resistor to the input of the module and that helped some. Next I moved the attenuator from inside the mini-box that encloses the amplifier and that helped some more. Finally, I retuned the transverter and "played around" with the ALC control in the Uniden HR-2510 that I am using for the i.f. That got the amplifier working properly and it is putting out very close to 20 watts which is the recommended power output for SSB. It will put out right at 40 watts on FM, and CW (the module is rated at a maximum of 45 watts output on FM).

But, I noticed that the receive mixer (a TA-7153 dual gate MOSFET) was getting hot. Now the basic sensitivity of the receiving converter is "OK", but nothing to write home about. Of course the mixer is "shot". The only dual gate MOSFETs that Mouser stocks are the NTE221 and NTE222. The 221 runs over $14 and the 222 runs over $12. As such, I am looking for a replacement that costs less. The RCA SK3050 is the same replacement transistor but, as far as I can tell, those are no longer available. Of course the "replacement" series have always been between 5 and 10 times the price of the "generic" transistors.

Radio Shack used to have the replacement dual gate MOSFET transistors for around $3 but those are no longer stocked. I believe that "somewhere" in my "stock" of old Motorola and General Electric spare parts that I do have at least one dual gate MOSFET. But, that is going to require some "looking" on my part.

I did get the 7/8ths inch Heliax run up my main tower and the 12 meter 2-element yagi down. The 7/8ths runs almost all the way into my main shack so I went the remainder of the way with 1/2 inch Heliax all the way to within 6 inches of where the 432 MHz station is going to be. Since 1/2 inch Heliax has considerably less loss than RG213/U the total feedline loss (even with the 2 different sizes of Heliax) should be less than if I had to use a 10 or 15 foot jumper of RG213/U. Now I have to "shinny" up the tower and install my 27-element 432 MHz yagi. That antenna will be right at 57 feet above ground. Since I live just 1/2 block from the highest point in the city, and it is "downhill" for over 300 degrees and "uphill" for about 15 feet elevation and then downhill again, I should do very well on 432 MHz.

The only thing left to do is to get my 4CX250B amplifier back on line. I need to build a new power supply (have all the parts) and change the bias from Class "C" to a linear mode. That will give me between 200 and 250 watts output.

Glen, K9STH

[K5UOS]

Glenn,

I have SK3050 and 40673 DGM's if you want either type. I have other types too.

A free DGM SMT source:

http://w7zoi.net/ke6f_lab.jpg

Let me know and I will send PPd and PDQ.

K5UOS

[K9STH]

I went through the Mouser website this morning and found 2 different dual gate MOSFET devices that should work. The basic specifications are very close except the noise figures which are considerably lower! The TA-7153 and NTE 221 have 5 dB figures and both of the SOT devices have 1 dB. One is 59 cents in single quantities and the other is 47 cents in single quantities. They are in SOT packages but it should be easy to solder leads and install on the circuit boards. At that price I am going to order several and see if they do work. If one of them doesn't work I'll get with you.

Since Mouser is on the south side of Fort Worth and I am on the north side of Dallas the parts will be here tomorrow afternoon.

Glen, K9STH

[K9STH]

UOS:

The SOT does work. However, the receive portion of the Microwave Modules transverter is not quite as sensitive as it was before the mixer transistor "went south". Therefore, let me know what you want for one of the SK3050 and I will try it.

If that doesn't improve the sensitivity then I will probably build a preamplifier.

By the way, the SOT devices are definitely small! I built a small circuit board on a piece cut from an old Radio Shack multiple pad "hobby" type board that had leads going to the primary circuit board. Then I soldered the SOT to that board. Had to use my magnifying lamp to see! Normally I don't have to use the lamp but in this case it sure was "handy". But, the SOT device is definitely considerably larger than when I worked for a company that produced thin film and thick film circuits (that was almost 40 years ago). The women on the assembly line used binocular microscopes when "wiring" the circuits. Since one of my duties as the applications engineer was occasionally doing quality assurance. That required my learning how to "operate" using a microscope.

Glen, K9STH

[W6GQ]

PM sent






8 9 10

[K5UOS]

Packed and sending this morning. No charge. Hope it works.

GL with the project Glen...K5UOS

[K9STH]

UOS:

Thanks!

Glen, K9STH

[AF6LJ]

Glen;
let us all know how it works, I've been following this thread with interest.
:)

[K9STH]

The replacement dual-gate MOSFET arrived late this afternoon. It definitely increased the basic sensitivity of the receiving converter section of the transverter by about 12 dB. That is the signal required is now about 1/4th what it was. However, the "front end" of the receiving converter section can still use a "little" help for those "really weak" stations.

I have quite a number of 2N4416 JFETs that supposedly have a noise figure of around 2 dB. There are plenty of preamplifier designs around for the 2N4416 that are very simple to build. Therefore, I am going to try one. If the basic sensitivity is still not adequate then the next thing is a GasFet preamplifier.

I also have a few MPF-102 JFET transistors which are similar to the 2N4416. However, they are 3-lead plastic case and not the 4-lead metal case of the 2N4416. Also, the MPF-102 tend to have a noise figure somewhat higher than the 2N4416. Fortunately, the Microwave Modules 432/28 transverter has separate inputs for the transmit section and the receive section. Therefore, adding a receiving preamplifier will be very easy.

If I was extremely serious I could mount the preamplifier at the top of my tower. However, that would require some serious work. Therefore, since I am feeding my 27-element simulated plane reflector yagi with 7/8ths inch Heliax I am going to stay clear of tower mounting any preamplifier for the time being.

Glen, K9STH

[K9STH]

I built a preamplifier using a 2N4416. It works but doesn't really do anything to improve the sensitivity. However, I found a "bad" solder joint (from the factory) in the Microwave Modules 432/28 transverter. When that was redone I now have an LDS (least discernible signal) of less than 0.05 microvolts which is the minimum value that my service monitor can "put out".

Glen, K9STH

[AC0FP]

I built a preamplifier using a 2N4416. It works but doesn't really do anything to improve the sensitivity. However, I found a "bad" solder joint (from the factory) in the Microwave Modules 432/28 transverter. When that was redone I now have an LDS (least discernible signal) of less than 0.05 microvolts which is the minimum value that my service monitor can "put out".

Glen, K9STH

So what is the brand of the service monitor and do you think its leaking? :confused:

Frank:)

[K9STH]

FP:

The service monitor is not leaking. Actually, I should have said that 0.05 microvolts is the lowest calibrated point on the attenuator. The service monitor can have the signal reduced to basically zero. However, that is below the minimum calibration on the attenuator dial.

I have two service monitors. One is a Motorola that actually was made by Systron-Donner and the other is a Singer/Gertsch. I normally use the Motorola because it can go up to 999.9999 MHz whereas the Gertsch only goes to 599.9999 MHz.

Glen, K9STH