EMRFD Message Archive 14216

Message Date From Subject
14216 2017-08-27 11:08:14 Ashhar Farhan Low voltage power amp
Our designs have been long normalized to 12v operations. At the moment, on the benxh here is an attempt at a reboot of the DSP10 with contemporary devices. An additional challenege has been to work at 6 volts.
Power amplifiers are proving to be a challenge. Even the J310 drops gain rapidly below 9 volts, mosfet power devices fail to deliver or report very high distortion. Are there specific pointers to low voltage power amplifications? I am guessing that mobile phone industry must have furthered the low voltage art.
I am trying to build a 1 watt output linear chain with 30db IMDc and about 40 db gain that works off 4.5 to 6 volts (4 nicad cells)
- f
14217 2017-08-27 15:17:56 wb8yyy_curt Re: Low voltage power amp

I am not a power amplifier designer, but this is my stab based upon basic principles.  I am thinking that many devices can be employed, but perhaps try bs170 or even 2n7000 mosfets.  see what power can be obtained at 50 ohm load, and try 2:1 and 4:1 transformers on the output.  honestly the recipe may be combining multiple devices in parallel, and maybe loaded into a common transformer.  I am suspicious that these 2 techniques might he combined in modern high frequency low voltage PAs.  I expect Rick, Dan and others to chime in.

14218 2017-08-27 16:04:30 wb8yyy_curt Re: Low voltage power amp
On second thought ....

some work on a low voltage power amplifiers has been conducted by Hans Summer and builders of the Ultimate 3S transmitter. 

the stock configuration is a single BS170 and a bifillar ouput winding -- this produces about 300 mW at 7 MHz with 5 volt bias.  so a little more at 6 volt bias. 

but my story unravels a bit with paralleling devices.  perhaps the reactive part of the network is hindering higher power at this bias level?  maybe other devices are more suited for your application.  worth reading what this community has determined - i don't have references but Hans may.

14219 2017-08-27 19:27:37 Ashhar Farhan Re: Low voltage power amp
Vk2zay has tried 2n7000 at these power levels. Hans' work has mostly been at the non-linear end. As Noted by EMRFD, MOSFETs need higher voltage for lower distortion. I need a linear power amplifier at low voltage that works at VHF.
I suppose I could drop in a power module, that would be no fun though.
- f

14220 2017-08-28 01:01:07 bubnikv Re: Low voltage power amp
The famous ATS-3b by Steve KD1JV produces roughly 1W at 5V with 3 paralleled BS170 in a class-E like configuration.
14221 2017-08-28 01:15:51 Ashhar Farhan Re: Low voltage power amp
I am looking for a linear amp at VHF. Something that can be used for digital as well as analog modes.

- f

14222 2017-08-28 01:54:10 Thomas S. Knutsen Re: Low voltage power amp
Farhan, you don't say what VHF band you are trying to experiment on. I'll assume 2M, altough most of this works on any of the VHF and low UHF bands.

Using a 7.2V power module is a option. The fairly new RA series from Misubishi has decent IMD (around your 30dB IMDC mark) at such low voltage.  Look at the RA07M1317MSA for a example of such module. 

Alternative, designing a discrete PA isn't that much different on 6V than its on 12V. Only remember that your output impedance is propotional to the square of the voltage, so your impedances will be low. For a VHF design, doing the impedance transformation with a PI or CLC circuit with the LPF works well.

For devices, I'd look at RD00HVS1 driver and RD06HVF1 or maybe RD15HVF1 devices for a total cost around $5. If you want bipolars instead of MOS, there is a lot to choose from, you may even get away with borrowing the devices from a older VHF Handie talkie, but be avare that when linearized those devices may have horrible IMD at such low voltage. Observe that older VHF and UHF devices may have low gain. Found some nice cheap 25W UHF transistors at a hamfest, but their gain is low at 5-6dB, 

That being said, have you considered using a boost converter to drive the PA? that way you can drive the PA stage at a higher voltage and gain some IMD preformance from that. A propper designed Boost should not make any noise at VHF, and you only need it turned on when you are transmitting. Personaly I'd aim for 24V, since this gives 5W with 50 ohms load impedance. 

Remember to keep wires short, and it should be like working at HF. 

73 de Thomas LA3PNA.

2017-08-28 10:08 GMT+02:00 Ashhar Farhan farhanbox@gmail.com [emrfd] <emrfd@yahoogroups.com>:

I am looking for a linear amp at VHF. Something that can be used for digital as well as analog modes.

- f

14223 2017-08-28 02:45:34 Riccardo Montagut... Re: Low voltage power amp
Good Morning,

Farhan I've recently buyed from aliexpress some RQA0009 mosfets, those are used as power amplifier in Baofeng UV5. (I bought them to repair one baofeng)
After that I had 9 unused mosfet so I tryed following the datasheet to build a VHF linear for the 2M band on copperclad (the mosfet is smd but not difficult to work with) the device is able to deliver up to 6W on FM with 0V gate bias and something like 5W in SSB (maybe is better to keep the power output a bit lower to run it cooler), I don't have the instruments to measure distortions but sounded good when received with another radio!
From specs it works exactly at 6V and has a linear gain of 18dB maybe could be great using it in push pull!

73 Riccardo
Inviato da iPhone

Il giorno 28 ago 2017, alle ore 10:01, bubnikv@gmail.combubnikv@gmail.com> [emrfd] <emrfd@yahoogroups.comemrfd@yahoogroups.com>> ha scritto:

The famous ATS-3b by Steve KD1JV produces roughly 1W at 5V with 3 paralleled BS170 in a class-E like configuration.

[Non-text portions of this message have been removed]
14224 2017-08-28 03:20:12 in3otd Re: Low voltage power amp
a push-pull of AFT05MS003N at HF gives quite good results at 7.5 V. The device should work well also at VHF but I did not yet try it there.

73 de Claudio, IN3OTD
14225 2017-08-28 04:09:22 NeilDouglas Re: Low voltage power amp



Mitsubishi shows VHF device -  RD02LUS2 as 2W at 3.6V, spec sheet shows 25dB linear range at 3.6V, they have Vdd – Po graph showing 4W out at 6V.


S Params on the data sheet are from 100MHz to 1.5GHz.




14226 2017-08-28 09:11:37 Ashhar Farhan Re: Low voltage power amp

Yes, I am trying to build a 2M transceiver with the teensy as the 'backend'. I also wanted to use 6v to 5v as the power supply to break out of the '12v' normativity.

Guys, thanks for pointing out these devices. It appears that there is more choice on VHF than HF! I will see what mouser can deliver from these.

- f

14227 2017-08-28 11:08:32 jim Re: Low voltage power amp
14228 2017-08-28 11:56:33 Ashhar Farhan Re: Low voltage power amp
Was this on 144 MHz?
- f

14230 2017-08-28 13:09:28 jim Re: Low voltage power amp
14231 2017-08-29 13:26:08 Sandeep Lohia Re: Low voltage power amp
How will U know when 4 nicad cells R fully charged? Or they needs charging?
Alternatively U can also use a mobile phone's lippo power bank...

U can also use buck booster for 12 V in TX mode, otherwise there will be more loss in Pi matching network with 5 V, can't use autotransformer...
& other issues

 2N4427 transistor will easily give 1 watt output, but will need a buffer in between...

For class C amp in VHF range linearity is questionable!