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Old 14th Oct 2018, 3:05 pm   #1
Bazz4CQJ
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Default MuTek Pre-amps for the FT290R

The 290 which I have is something I only picked up a couple of years ago, but looking at Google there are frequent comments about fitting the Mutek pre-amps. However, MuTek went out of business a long time ago, so the information I'm finding is a bit thin and scattered.

Can anyone give me a crash-course of the why's and wherefore's on this; is the 290 Rx really that needy. I've seen reference to a lossy PIN diode being replaced by a changeover relay?

Thanks
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Old 14th Oct 2018, 3:55 pm   #2
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Default Re: MuTek Pre-amps for the FT290R

I've owned a couple of original 290's and never once thought they lacked sensitivity.
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Old 14th Oct 2018, 4:28 pm   #3
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Default Re: MuTek Pre-amps for the FT290R

The Japanese manufacturers latched onto sensitivity as their main marketing figure and competed against each other with it. Most of their radios were not short on sensitivity. Rather the reverse. In trying to get lots of sensitivity, their designers took their eye off the ball in terms of overload and non-linearity.

What Chris did with his MuTek front ends was to fix the overload issues so that radios were still useful when there was a pager transmitter banging away several megahertz away or another amateur at the other end of the village.

Don't fit one expecting any sort of revelation in increased sensitivity. Look for one if you're suffering blocking.

Chris Bartram is a very skilled RF designer with a good sense of compromise for all the interacting factors and produced a nicely balanced design... he still does. There are new things from him keep appearing in the microwave groups, and he has been known to play the fiddle at the dinners after meetings of the microwave roundtable. He's still very much on the go, but closed down Mutek and moved into consultancy many years ago.

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Old 14th Oct 2018, 5:02 pm   #4
G4YVM David
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Default Re: MuTek Pre-amps for the FT290R

It was a glorious fashion item for those os us suffering from front end envy c 1980...thats all of us then.

Ive a xx rig 'with a mutek front end'. I still feel good saying it.

Did they resurrect the dead? No.

Even the beautiful FT225RD 'with a mutek front end' was good...possibly very good, but whether its enjoyment factor was enhanced by mutek I dont kniw. Having said that...I STILL want one ...never did get one.
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Old 14th Oct 2018, 5:24 pm   #5
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Default Re: MuTek Pre-amps for the FT290R

My FT290R mk1 has the Mutek preamp fitted and my main issue with it is (in)stability.

It goes unstable when using the whip antenna unless the whip is fully extended and is kept away from other objects. Of course, this would be normal practice but it isn't nice to hear it generating noise and birdies unless it sees an antenna load it likes. It also hoots when removing the coax fed antenna with the whip fully down.

I think the gain can be tweaked down in order to balance NF vs signal handling and I do remember turning this down slightly. I haven't bothered to adjust the front end tuned circuit but I suspect that it was tweaked (by whoever fitted it) for max gain rather than lowest noise figure. I recall that I got an overall receiver noise figure of 2.5-3.0dB with the Mutek preamp when I last played with this radio on my workbench. I suspect it can be adjusted to be better than this but I doubt there is much point because of the band noise level where I live.
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Old 14th Oct 2018, 5:53 pm   #6
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Default Re: MuTek Pre-amps for the FT290R

I have one of the original Mutek Front Ends in an FT221R. I still have the original Yaesu front end too. There is very big difference between them and the Mutek one is never coming out.

It replaced a JFET mixer with a well terminated diode ring followed by a 10.7MHz 15kHz BW roofing filter. The RF amp is a BF981.

Did they do all this for the FT290 or was that one (as titled) just a pre-amp?
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Old 14th Oct 2018, 6:14 pm   #7
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Default Re: MuTek Pre-amps for the FT290R

In the case of my mk1 FT290R the Mutek board is just a little PCB of size approximately 50mm x 35mm. It contains a small TR relay and a dual gate Mosfet amplifier. There is also a tuned circuit at the input to the Mosfet and a simple lumped BPF at the output. Just after the Mosfet there is also a tiny series trimmer resistor that is part of a resistive pi attenuator that can be used to vary the overall gain.
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Old 14th Oct 2018, 8:07 pm   #8
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Default Re: MuTek Pre-amps for the FT290R

Thanks all for the comments.

Quote:
Originally Posted by Radio Wrangler View Post
Don't fit one expecting any sort of revelation in increased sensitivity. Look for one if you're suffering blocking.
I am out in the sticks and deep in a hole; I can only get one mobile phone service here and that is not 100%. Blocking should not be a problem at this QTH .

B
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Old 14th Oct 2018, 8:16 pm   #9
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Default Re: MuTek Pre-amps for the FT290R

OK Bazz and Jeremy, then it sounds like a pre-amp as described.
Cirkit also did something tiny for 2m with a 3SK88 if I recall.

My Mutek equipped 221 does have some surprising behaviour.

I have never detected any signs of instability from it, but sometimes it hears far off things you might not expect to hear. Then you find it doesn't even have an antenna connected.

Sounds strange? It certainly is.
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Old 14th Oct 2018, 9:09 pm   #10
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Default Re: MuTek Pre-amps for the FT290R

I tried to take my mk1 290R apart to show an image of the Mutek board but I stopped part way because it proved harder than I thought to get it out! So I stopped and put it back together. But the good news is that the Mutek board now seems stable. I think by trying to remove the whip assy and the plates around the Mutek board and then refitting them I've improved the RF grounding in some way. The Mutek board seems much better behaved now as I extend the whip. Before, it would go hissy and deliver wandering birdies as the whip was extended.

However, I also took it apart to clean out the black residue from the decaying black sponge inside the top cover. This residue was falling into the radio and making a real sticky mess. This is all done now and the radio looks much cleaner inside. I've removed all of the original sponge so I'll have to find a replacement sponge from somewhere.

I think in the case of the 290R the Mutek board helps with sensitivity but the idea is to turn down the gain with the trimmer resistor so it just gives a useful improvement without causing any overload effects from local signals. I don't know what the sensitivity of an unmodified 290R is but a lot of 2m radios of this era had a NF in the region of 6-8dB. So not that great. The datasheet for the mk1 290R suggests the receiver has a NF of <= 7dB.

In 2018 I'm not sure this matters because of the higher band noise today but I recall that back in the 1980s there were several classic 2m multimode radios that were classed as deaf and this included the Trio TR9130, the Yaesu FT290R and the Yaesu FT225.

The best cure for the deafness was a masthead preamp but in those days there could be 6 operators within 2 miles of your house so overload was often an issue. So I think the more exotic Mutek boards were designed to improve the noise figure and the signal handling. They did this with a low loss TR relay, a low noise amplifier and a better mixer and sharper IF filtering. But for a portable radio like the 290R the popular choice was the little internal Mutek preamp and I do remember that most users were pleased with them. I would expect the Mutek board to improve the noise figure to somewhere close to 2dB. I could measure mine again after rebuilding it but I expect it will be somewhere around 3dB or so because I turned down the gain a fair bit on mine.
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Old 14th Oct 2018, 9:17 pm   #11
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Default Re: MuTek Pre-amps for the FT290R

Quote:
I have never detected any signs of instability from it, but sometimes it hears far off things you might not expect to hear. Then you find it doesn't even have an antenna connected.

Sounds strange? It certainly is.
I think that one of the tricks used by Mutek on their bigger 2m boards was to use an unscreened inductor in the RF network ahead of the first LNA. This also didn't have a ferrite slug and so the overall Q of the inductor was higher. So this helped with the noise figure a bit but it would also act as a tiny pickup antenna. They also used unscreened Toko coils in the post LNA BPF and presumably this could pick up signals too.

By contrast, Yaesu often used screened coils with ferrite slugs ahead of the LNA and they used screened helical filters after it. This would have more loss but was probably less likely to pick up signals with no antenna fitted.

However, my little Mutek board in the 290R does use screened inductors so they didn't always try for optimum Q in the front end network.
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Old 15th Oct 2018, 7:57 pm   #12
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Default Re: MuTek Pre-amps for the FT290R

I think that is pretty close to the nub of the problem.

It just ends up surprising me from time to time. Obviously the lids with their snap on
buttons do not do very much to screen the front end since they are painted and approaching lambda/4 on a side.

It wouldn't fair well in a shack that was hot with 2m RF from a computer or such.

Some ATU manufacturers (one is quite well known- I mention no names) could take some lessons from Chris about spacing around HighQ inductors...
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Old 15th Oct 2018, 10:06 pm   #13
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Default Re: MuTek Pre-amps for the FT290R

Yes, on some Mutek boards the aim was to minimise losses and get a low noise figure but this was combined with a diode ring mixer and a strong IF amplifier and a narrow IF filter.

On the mk1 290R the radio has to support the internal whip option and I think this must affect the front end losses a bit. However, I've never tried to measure these losses. So although the little preamp probably has a noise figure of <= 1dB I think the overall receiver noise figure will be degraded by the need to support the whip antenna. I tried to find a spec for the receiver NF when the Mutek board is fitted to a mk1 290R but couldn't find one. I suspect it will be somewhere between 2 or 3dB but this depends on those front end losses associated with the whip antenna.

When I measure the noise figure I do it with an Agilent noise source and I use the Y factor method. I look at the receiver AF output on an analyser and set a noise marker in the AF passband with the noise source off. Then I turn the noise source on and measure the noise level again. These two noise levels can be used to calculate the Y factor and if the noise source ENR is known (eg 5.73dB ENR) the noise figure can be calculated with fairly low uncertainty using a fairly simple and classic equation. The hot/cold VSWR of the noise source is really low so this minimises uncertainty. I also have a Noisecom noise source and the results with this noise source usually agree very closely with the Agilent noise source.

By contrast, I think a lot of technical reviewers just measure SSB 'noise floor' with a sig gen and they declare the noise floor to be the sig gen level that boosts the AF noise level 3dB. But this isn't a reliable method for various reasons.
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Old 18th Oct 2018, 11:08 pm   #14
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Default Re: MuTek Pre-amps for the FT290R

If it helps I dug out my old Trio/Kenwood TR9130 2m multimode and had a play with it. Back in the mid 1980s the TR9130 was one of the radios classed as being a bit deaf and I did a few quick tests on mine. I've never tried to align it as I've never actually used this radio in transmit (no microphone came with it) and it shows a noise figure of about 8.5dB when I test it with the noise source with the TR9130 set to SSB mode.

The sensitivity specifications for this radio are potentially confusing because of the 6dB difference between uV EMF and uV PD for a receiver with a 50 ohm input. However, I think the Japanese radios are spec'd in the glossy brochures using uV PD but in the service literature the alignment checks are done in dBuV EMF.

So this is potentially confusing! The alignment check in the service manual says in SSB mode the sensitivity for a European (144-146MHz) TR9130 is -8dBuV for 10dB S/N. So this is 0.4uV EMF or 0.2uV PD. This is also in S/N rather than S+N/N.

This roughly translates to a noise figure of about 9.2dB and presumably this will be at the 2m band edges where the sensitivity might be slightly worse.

So my radio is probably quite typical if it measures the noise figure to be about 8.5dB near the middle of the UK 2m band. The spec for a stock Yaesu FT290R in SSB mode is 0.5uV for 20dB S/N and this means the noise figure must be somewhere around 7.2dB.

So the 290R is probably only slightly better than the TR9130 in terms of sensitivity. If we assume the Mutek version can be optimised to get a 2.2dB noise figure then that's up to about a 5dB improvement max. However, once you factor in a ballpark antenna noise temperature at 145MHz of 600K (under fairly favourable conditions for galactic noise etc) and maybe allow about 1.5dB feeder loss the difference between the radios will be reduced to maybe 3dB at times. On a noisy band there will be very little difference at all.

Back in the 1980s when I was active on 2m SSB, there were some very serious operators chasing contests and awards and for them every dB improvement in S/N really mattered. However, in 2018 a fairly casual operator on the 2m SSB band probably won't get to notice/appreciate the difference because the band is noisier today and a difference in S/N ratio of maybe 2 or 3dB isn't that significant unless you are desperately trying to make contacts right down in the noise to grab another locator square or county/country or to get a few more points in a contest.
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Old 18th Oct 2018, 11:23 pm   #15
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Default Re: MuTek Pre-amps for the FT290R

To show why a typical setup using the TR9130 was classed as deaf I put together a quick spreadsheet for antenna temperature, feeder loss and receiver noise temperature (converted from noise figure in dB).

I compared a TR9130 fed via coax with 1.5dB loss to a typical 'serious' setup using a masthead preamp with an overall receiver noise figure of 1.2dB.

I compared the difference using a slightly elevated beam that was pointing in a direction with low galactic noise. I really can't remember how quiet the 2m band noise can be when this is done but I chose an antenna noise temperature of 250K.

So when both are fed with the same antenna there is a difference in S/N ratio of about 7dB. This is because the TR9130 has an 8.5dB noise figure and this is made worse by a typical (longish) feeder loss of 1.5dB. However, if the antenna noise temperature shot up to a not unreasonable 2000K the difference between the TR9130 and the 'serious' setup falls to about 3dB.

So the decision to adopt a low noise preamp depends on what you want to do with the radio and also on how noisy the band is. To really appreciate the difference in 2018 you would probably have to be beaming your antenna in a quiet direction. Maybe someone with experience of the 2m band today can comment because I really don't know how low the rural/urban band noise can go on 144MHz in 2018 when a beam is rotated around at various times of the day/month.
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Old 19th Oct 2018, 2:39 am   #16
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Default Re: MuTek Pre-amps for the FT290R

Be wary of measuring noise figure of complete receivers, you want to be sure there is no agc action at either of the two levels of noise. Any gain reduction or compression of the higher level distorts the result and makes it look better than it really is.

It can be worth comparing results with both 15dB ENR and 6dB ENR sources.

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Old 19th Oct 2018, 1:15 pm   #17
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Default Re: MuTek Pre-amps for the FT290R

Yes, there are a few potential gotchas with the noise source method. My Agilent noise source ENR is typically 5.7dB and the Noisecom ENR is 13.6dB and I check with both.

I do also make sure there is no compression by running the AF at a suitable level with plenty of headroom. The other issue is noise pickup and I always check across several channels to make sure the radio isn't picking up any local noise or mush. The shape of the noise and any internal birdies can be seen easily on the analyser so this helps reduce the risk of a false result. Ideally, it should be done in a screened room. I've got lots of experience at work (getting strange results!) using the old HP8970B noise meter unless it gets used in a screened room. But here at home I rarely see any noise or interference pickup.

I also use the conventional method with a sig gen but the result depends on the tone frequency on SSB as the passband usually isn't flat. So even with a tiny change in test frequency the results can vary a lot. I've also experimented with a small amount of FM with the sig gen to spread the energy across the passband to get a more realistic result when using this method.
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Old 19th Oct 2018, 1:43 pm   #18
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Default Re: MuTek Pre-amps for the FT290R

The 8970 uses a diode detector and its response is a bit affected by the probability density function of the noise, and not all noise creation mechanisms are dependably Gaussian.

Resistor thermal noise is pretty Gaussian stuff, but noise from avalanche mechanisms gets a bit interesting at lower levels. So I stuck a proper true RMS detector in the noise figure analyser that replaced the 8970. People had driven the noisiness of a lot of devices down so low that the difference was beginning to show.

I had an interesting moment when evaluating some new noise diodes. Their output level was increasing as I decreased the bias current. Increasing quite dramatically. What would happen if I turned off the current? would the noise density go to infinity and cause a new big bang setting off the next universe? That was happening was the bandwidth of the noise was coming crashing down, so the total output power wasn't doing anything silly... but I was looking at the density and at a fairly low frequency.

Life has its little surprises!

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Old 20th Oct 2018, 9:56 pm   #19
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Default Re: MuTek Pre-amps for the FT290R

I've got various Noisecom (diode based) noise sources here and I think they all show a slight increase in noise level if I reduce the reverse voltage slightly. I use this feature as a fine tune when setting the noise source via a 1dB step attenuator. When I use these noise sources for a critical task I have to set the reverse voltage accurately using a decent DMM to get it set to 28.00V.

Getting back to the Mutek debate, I dug out a DSP based SINAD meter today and measured the Mutek mk1 FT290R on FM. This DSP based SINAD meter has an ultra sharp AF notch and it is just a few Hz wide. I've done various tests on it over the years using a noise source and a precision step attenuator to prove how accurate it is.

This test method means using a sig gen set to a 1kHz test tone with 3.5kHz deviation. I tried three sig gens and they all agreed very closely in the following test.

The spec for a stock mk1 FT290R in FM mode is 0.25uV PD for 12dB SINAD and my Mutek FT290R managed 0.145uV PD for 12dB SINAD in FM mode. So there is a definite improvement compared to the spec at least. Note that I didn't select any SINAD AF bandpass filter options in the SINAD meter and left the meter filtering to 'flat'.

When testing in SSB mode, I'm not sure when the AGC kicks in on the Mutek 290R but I think it is still some way off from the levels generated by my noise sources. I think any AGC or compression that kicks in with the noise source turned on will make the noise figure appear slightly worse when done with the method that I use.
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