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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 11th Nov 2017, 4:35 pm   #21
Philips210
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Default Re: Power transistors in receiver front ends.

Hi.

The excellent Magnetic Loop Aerial Amplifier By Gary Tempest uses medium power transistors (2N5109s). Have a look at this thread for the circuit diagram etc. http://www.vintage-radio.net/forum/s...d.php?t=137089

Regards
Symon
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Old 11th Nov 2017, 6:46 pm   #22
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Default Re: Power transistors in receiver front ends.

Quote:
Thanks for the explanations, David & Jeremy. I've never come across thesee devices, despite working with electronics for almost 50 years
In case you haven't heard of them, the other common type is the classic HBT transistor which is a heterojunction type of BJT. Often Silicon Germanium (SiGe) is used but the other popular type of HBT is based on InGaP technology. See the stuff linked below for Indium/Gallium/Phosphide or InGaP.

https://en.wikipedia.org/wiki/Indium_gallium_phosphide

SiGe and InGaP HBTs have been around for many years (decades) and they offer very good performance up into the GHz region. They can also be used down at VHF.

An old school HBT such as the Stanford/Sirenza (now Qorvo) SBB-1089 is a cheap and small MMIC amplifier that uses InGaP technology. This device has been around for 15-20 years and it would make a fairly respectable front end amplifier for use in the VHF high band at 175MHz for example.
It typically runs from just +5V at 90mA and offers about 15dB gain and a noise figure of about 3dB at VHF. Nothing too spectacular so far but it does offer a +43dBm IP3 performance which is very special in terms of large signal handling.

http://www.qorvo.com/products/p/SBB1089Z

I've used the SBB4089Z and SBB5089Z parts loads of times at work as they offer flat gain and decent signal handling up to 4GHz or so. However, the 850MHz SBB1089Z is probably a better choice for use down at 240MHz. If two of them were used in push pull it would make a great VHF>UHF wideband amplifier with decent IP2 and IP3 performance. Not a bad benchmark to compare others against?

InGaP is generally very rugged and reliable and very linear but these small MMIC devices are generally sub 100mW devices. However there are larger InGaP devices that run at higher power levels than this.

If you look at the periodic table of elements there is a area within it that contain the usual suspects used for semiconductor physics. See the image below where I've circled a few elements in the group III, IV and V columns.
You can see Silicon, Germanium, Gallium and Arsenic in the yellow and green circles. The other elements in the white circles get used for doping. But you can see they are all close neighbours on the table.

TriQuint was a huge semiconductor manufacturer for many years (now owned by Qorvo) and the company got its name from the periodic table. It specialised in GaAs parts and Gallium is a group/column 3 (III) element and Arsenic is group/column 5 (V) so the III+V led to Tri+Quint.
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Old 11th Nov 2017, 7:00 pm   #23
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Default Re: Power transistors in receiver front ends.

Be aware that although some of the interesting compound semiconductors may be great at microwave frequencies, they can be stinkers at HF and even VHF with dramatic riises in noise figure at the low end.

TriQuint started life as part of Tektronix and has recently merged with RFMD to form Qorvo.

If I remember right, Wes Heyward of amateur radio fame went to TriQuint when it was spun out.

David
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Old 11th Nov 2017, 10:15 pm   #24
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Default Re: Power transistors in receiver front ends.

The TriQuint name was nicely chosen! The periodic table is one of those permanent mental impressions from one’s early days of studying science matters. Along that vector, perhaps a company specializing in SiGe type devices might have named itself as TetraQuad. Mixing Greek and Latin derivatives appears to be accepted practice, perhaps even de rigueur in electronics. (But then TetraQuad sounds a bit close to tetraquark, something not associated with longer-term stability.)

Another HF receiver that used a 2N5109 in a feedback circuit as a wideband RF amplifier was the Drake R7 of 1978. This was at the upper end of the consumer class.

The Redifon R551 used a 2N3866 pair in class A push-pull with feedback. The Racal RA1772 used a BFX48 and a BFW17A. The latter described as being intended for CATV service, so was in the same category as the 2N3866 and 2N5109.

So, the evidence is that bipolar power transistors (typically those designed for CATV service) were used as RF amplifiers in professional and upper consumer level HF receivers over the period from c.1968 through to the mid-1990s at least.

A possible VHF-UHF example at the consumer level was the AOR AR2002 scanning receiver of the later 1980s. This had wideband RF amplifiers using thick-film hybrid ICs, the MC-5800 below 550 MHz and the MC-5805 above 800 MHz. The MC-5800 was described as a wideband CATV amplifier, so it appears to have been intended to do a similar job to the 2N3866 and 2N5109, although at lower current consumption. Thus, it might not qualify as a power RF device. The MC-5805 was described as a wideband amplifier for direct broadcast satellite systems.

The contemporary ICOM R7000 tunable VHF-UHF receiver used tuned dual-gate mosfet RF amplifiers up to 1 GHz. That aligned with Japanese HF receiver practice of the time (ICOM, JRC, Kenwood) where dual-gate mosfets or small-signal jfets were used as RF amplifiers. But then these were intended mostly for use with relatively small “domestic” aerial systems, not with professional aerial farms. Possibly the use of power devices as RF amplifiers in consumer-level receivers such as the McKay Dymek series was as much to facilitate a wideband amplifier (for which small-signal fets were less suitable) as it was to provide very good signal handling capability. Though the AOR AR7030 was evidently designed with the high level of signal-handling capability to suit typical European reception conditions.

Returning to the ICOM R7000, for the 1 to 2 GHz range it used a converter that had a wideband RF amplifier using a 2SC2367 bipolar device. I’m not sure, but this appears to have been on the borderline between the small-signal and power devices. In a similar category may have been the BFR90, used as an aperiodic 1st RF amplifier in the Eddystone 1990S professional UHF receiver of the late 1970s. I suspect that the original question probably referred more to transistors, such as the 2N3866 and BFW17A, that could definitely said to be power devices.


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Old 12th Nov 2017, 1:27 am   #25
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Default Re: Power transistors in receiver front ends.

Quote:
Be aware that although some of the interesting compound semiconductors may be great at microwave frequencies, they can be stinkers at HF and even VHF with dramatic riises in noise figure at the low end.
Yes and they can also have stability issues at low frequencies. At work the SBB-5089Z HBT (InGaP) MMIC is a popular device but the Qorvo datasheet specs all start at 50MHz including their own official s parameter data. I have measured this part on a VNA in the past and below about 30MHz this part is no longer unconditionally stable. But if you use the Qorvo S2p data you would never know because it sneakily avoids this region below 50MHz. The gain also creeps up below about 20MHz and I think that some of the internal feedback within the device starts to fade away below 30MHz. To make it oscillate I recall that the output needs to be presented with a high impedance (eg an open) and the input needs to see a shunt inductance of a few uH and the part will oscillate strongly at a few MHz. So it probably wouldn't be a good idea to use this part between some RF filters down in the lower SW bands. It could turn into an oscillator.

The SBB-1089Z is spec'd down to 50MHz with about a 3dB noise figure and with a very high OIP3 performance so it would perform well up on the old VHF high band I think. I've never measured one on a VNA below 50MHz for any potential instability issues though...
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Old 12th Nov 2017, 3:02 am   #26
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Default Re: Power transistors in receiver front ends.

I've had just that sort of fun with the old Watkins-Johnson AH312. The available gain ramps up dramatically at the LF end, and although the strip begins with a nice impedance stabilising pad, the match that the device's s11 forces on me at the intended operating frequency prevents the device from seeing the nice real impedance at LF. If I try to engineer an LF connection, it involves relatively large inductance and all hell breaks loose. Getting a proper match on the wanted frequency is easy, doing it while also presenting the part with a damping impedance across all the frequency range it can oscillate over is a bit awkward.

Qorvo have just made the AH312 NRND, so I get to pick something less challenged on the stability front.

The moral in the story, for any innocent bystanders, is that exotic, fast, parts can be big trouble at lower frequencies.

People used to talk about "VHF construction techniques" and UHF ditto. These continue into styles of PCB layout and circuit design. The sting in the tail is that the level of technique needed to use any device is NOT set by the frequency you intend to use it at, but instead has to be good over all the frequency range the device has enough gain to make oscillation possible.

This applies in the valve world as well. Attempts to use bottles usually seen in TV tuners for audio circuits can oscillate at VHF/UHF. Using RF power valves in audio amplifiers is similarly fraught. The audio world keeps trying this in response to what its own demand for NOS audio valves has done to their prices.

David
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Old 12th Nov 2017, 6:12 pm   #27
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Default Re: Power transistors in receiver front ends.

Using devices at frequencies outside their design-spec can most definitely be 'interesting'. I once built a small solid-state HF transmitter and for the PA used one of the 'capstan' style bipolar transistors more usually found in VHF AM transmitters. Because that's what was in my junkbox.

Taming it was kinda interesting. Gain rises *rapidly* as frequency falls - so lots of VHF-lossy ferrite beads and low-value stopper resistors! but the gain was really rather spectacular at 7MHz. So much so that I could build a solid 25-Watt tx using only four transistors [2N3819 VFO, BC109 buffer, 2N3866 driver and the BFwhatever output stage].
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