# Transistors : 'Frequency' and 'RF' term

#### Willen

Joined Nov 13, 2015
327
Hi all,

Sometime I found a term 'RF transistor' to a simple TO-92 transistor which has transient frequency little higher than 300MHz. In this case do we need say RF transistor to a UHF transistor?

Also there are some transistor can go to some MHz like BD136 (maybe) and I found somewhere used as 7MHz ham radio RF driver stage. But we do not say it RF transistor. MRF476 (3 watt) also called RF transistor with 3W power and has 50MHz fT, but 2N3904 has 250MHz fT and it's called General Purpose transistor.

Trying to understand specialty of 'RF' (Radio Frequency) term and chemistry on transistor in such case.

#### Papabravo

Joined Feb 24, 2006
18,090
At low frequencies many types of general purpose transistors can be used for RF applications. Are they ideal? Probably not. Do they work? Sure, to some degree. How much do they cost? Small pocket change. As you go up in frequency things get more complicated. Designers need more information about a device over the frequency range of interest. RF transistors have more characterization data in their datasheets. This data is obtained with an instrument called a Vector Network Analyzer. A low end one costs more than a fancy sports car, and a really good one costs more than a medium sized house. These instruments are not common among the hobbyist community. People who do this for a living need to understand how the various parameters of a transistor might affect their designs so they do a lot of component characterizations and testing. They certainly don't take the manufacturer's word for anything.

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
This data is obtained with an instrument called a Vector Network Analyzer.
@Willen
If you can 'live without' 'bells and whistles', there are a few high quality instruments available at very reasonable (i.e. 'hobbyist friendly') prices, FOR EXAMPLE

Disclaimer -- No, I don't own the linked model and yes - the price seems to good to be true! That said Agilent (Keysight) has never let me down! -- 'Tho I advise that you attend carefully to option selection prior to ordering!

As regards re-characterization of semiconductors:

As one of many examples; I've personally had excellent results applying SD1407s to VHF power Amps (Specifically 2M ≈ 144 MHz) for many years -- Though, as per @Papabravo, 'off list' application of devices requires re-characterization of, I might add, each lot if not each device (my preferred approach)!

Best regards and have fun!
HP

PS -- I am not an Agilent/HP/Keysight Shill!!! -- Merely a satisfied customer!

#### Papabravo

Joined Feb 24, 2006
18,090
26 bills is a hobbyist friendly price!? That's still the price of a family sedan rather than a fancy sports car.

#### Aleph(0)

Joined Mar 14, 2015
597
26 bills is a hobbyist friendly price!? That's still the price of a family sedan rather than a fancy sports car.
I say HP's being too nervous about being called elitist For less than twice the price OP can have E5080A which she/he won't outgrow as fast!

HP I say you need to calm down! When you said workers sold their time for just money that was being crass of you cuz they were selling their time to maintain quality of life which is totally different! HP I know you know that now! But suggesting to buy $#!tty instrument because dirt cheap is rude in another way! A NICE low end VNA (which is like E5080A) for less than$50,000 is very good suggestion even before options! It's not being elitist at all! Is like you're always saying to me _it costs what it costs_

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#### GopherT

Joined Nov 23, 2012
8,012
@Willen
If you can 'live without' 'bells and whistles', there are a few high quality instruments available at very reasonable (i.e. 'hobbyist friendly') prices, FOR EXAMPLE

Disclaimer -- No, I don't own the linked model and yes - the price seems to good to be true! That said Agilent (Keysight) has never let me down! -- 'Tho I advise that you attend carefully to option selection prior to ordering!

As regards re-characterization of semiconductors:

As one of many examples; I've personally had excellent results applying SD1407s to VHF power Amps (Specifically 2M ≈ 144 MHz) for many years -- Though, as per @Papabravo, 'off list' application of devices requires re-characterization of, I might add, each lot if not each device (my preferred approach)!

Best regards and have fun!
HP

PS -- I am not an Agilent/HP/Keysight Shill!!! -- Merely a satisfied customer!

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#### GopherT

Joined Nov 23, 2012
8,012
@GopherT How is used market for NAs? Also I say if highest official in land can live on $350/mo then US to Napal exchange rate has to be way better than unity? Cuz I don't think anyone can live on that anywhere in North America unless survivalist or like that! A big fraction of Nepal lives on zero - off the land, and off the grid. #### Aleph(0) Joined Mar 14, 2015 597 A big fraction of Nepal lives on zero - off the land, and off the grid. GopherT I know it sounds trite but I'm saying just thinking about that really makes me count my blessings! Thread Starter #### Willen Joined Nov 13, 2015 327 Hi, Yeh, I recently got a middle-class government job and I am getting paid$175 per month. Buying foods and clothes inside the country is enough (not enough for luxurious life). BUT Buying things from abroad is very painful. Eg. If I need to buy a 100cc motorbike from India, I need to earn whole 8 months. And practically it's impossible because within these 8 months, money goes to home (to buy daily life's necessary things) too. So still mane people are watching 'black and white' TVs which are decades old.

If any American came here as tourist, he could live luxurious here few months spending few thousands dollars. (a level of 'luxurious' for me).

Do anyone can say how they make 'RF' transistor which is different than general purpose? And how they make high gain, high voltage, low noise too?

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#### Hypatia's Protege

Joined Mar 1, 2015
3,226
The OP is from Nepal. The prime minister makes about \$350.00 per month and is one of the highest compensated people in the country. Unless you are donating something, I don't think it is going to happen.
Well... I suppose one could 'walk through it by hand' with the aid of an 'antenna analyzer' still....

Sincerely, best of luck!
Very best regards
HP

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
About RF transistor: Do anyone can say how they make 'RF' transistor which is different than general purpose? And how they make high gain, high voltage, low noise too?
I apologize that I don't understand the question? Are you inquiring as to how the devices are fabricated or merely the distinction?

Best regards
HP

#### Willen

Joined Nov 13, 2015
327
I apologize that I don't understand the question? Are you inquiring as to how the devices are fabricated or merely the distinction?

Best regards
HP
I mean how manufactures make such special transistor? What they make changes around PN junctions? Maybe hard question and need manufacturer engineer.

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
I mean how manufactures make such special transistor?
I can't help you with that (IOW - I have no idea) -- Howbeit I'm certain someone on these fora can

Best regards
HP

#### Aleph(0)

Joined Mar 14, 2015
597
I mean how manufactures make such special transistor? What they make changes around PN junctions? Maybe hard question and need manufacturer engineer.
Willen That's fair question so I say thread needs bump!

#### Aleph(0)

Joined Mar 14, 2015
597
Howbeit I'm certain someone on these fora can
HP I agree! Someone on form must know that! So now thread has second chance

#### Hypatia's Protege

Joined Mar 1, 2015
3,226
Do anyone can say how they make 'RF' transistor which is different than general purpose? And how they make high gain, high voltage, low noise too?
@Willen
Please have a look at this application note although not a treatise on device construction per se, I believe you will find that it affords insight (at least) into many of your questions (Re: RF devices)

Here is a pleasingly quantitative discussion of HV/High power devices -- although the linked paper centers upon SiC technology - 'general principals' apply

Hope this helps! -- Should you have further or specific questions please let me know!

Best regards
HP

PS
My apologies for neglecting this thread! and many thanks to @Aleph(0) for rescue of same from the 'cyber scrap-heap'