The Yaesu MTU-160, -80/40 and -30/20 were designed as the ultimate in (internal) RF front-end protection for Yaesu’s top of the line, no expense spared FTDX-9000 tranceiver. Yaesu later developed somewhat funky external packaging (looks like a high-end techno-Deco stereo component fron the ‘90s) for these units, to allow them to be used (externally) with other transceivers, including the present day FTDX-5000, -3000 and -1200.
In previous reviews, the MTU units have variously been called a charade (fake gear that does nothing but looks like it does to ignorant users) or a wonder tool for improving reception (presumably by the ignorant users). I purchased all three to use and test, both with lab equipment and connected to a well-used FTDX-3000. And have formed some (free) opinions.
Note that my 5-star rating does NOT mean you should buy them. They solve a very specific problem, and if you do not have that problem, you don’t need them and will probably disappointed with their lack of usefulness.
IN SUMMARY:
1. The Yaesu MTU-160, -80/40 and -30/20 are very solid, well made passive/tuned RF pre-selector units, and were initially quite expensive – now much cheaper on the used market, particularly since few stations need them and so many operators have no idea how too use them. 2. They really work, and work well, to solve a specific problem – out of band interference, 3. Yaesu instructions and marketing can be misleading to operators who do not pay attention to details and do not understand the context Yaesu marketing and instructions are written from. 4. Because of their unusual design, they can be placed between a receive antenna and ANY brand of receiver (do NOT TX through them) when used as a fixed, very narrow band-pass filter. Some have reported very good results when paired with the Icom IC-7300. Tuning, if desired, must still be done using the Yaesu control protocol.
MY THOUGHTS ON COMMON MTU QUESTIONS:
Should you buy these units? Are they worth whatever you pay for them (used or not)?
YES – but only if you regularly suffer from strong but out of band interference, either industrial (like a nearby AM BCB station) or under Field-Day like conditions. Because the MTU filters are too broad to mitigate in-band interference well, though they are MUCH narrower that most RX band-pass filters. Because they are tunable, it is possible to attenuate nearby in-band interfering signals to a degree, but they are not really suitable or designed to do that. The 1st IF (sometimes called “roofing”) and (typically) 2nd IF filters (either digital and continuously variable or fixed/switched/crystal) in your receiver have MUCH better selectivity with the 2nd IF filters specifically having the job of suppressing interference very close in.
Why don’t the MTUs help with nearby interference? Yaesu says they are “Ultra-Sharp”. Are they lying?
Yaesu markets the MTU filters as providing “…ultra sharp RF selectivity for the front end of the transceiver”, and that is EXACTLY what they do, and they do it WELL, with a typical 6db bandwidth of 40-60 KHz (with a typical, measured insertion loss of about 6db, not much) compared to perhaps 1-6 MHz for a typical band-pass filter. In context, the MTUs are “Razor Sharp” compared to the band-pass filters. Remember too that Yaesu said “RF selectivity”, not “IF selectivity” or “channel selectivity”, and they said “…for the FRONT END of the tranceiver”, i.e. before ANY active electronics. If you’ve really read and understood this, you’ll immediately realize this is NOT the filter to use to tune out Ralph, next door, running 1.5 KW, just 2 KHz away. But if Ralph is one band down or up, this will do the job just fine, defending your receiver’s front end from overload with minimal signal of interest attenuation (a pure attenuator cannot do this) and in combination with your IF fiilters for final channel selectivity. That’s what its for. When examining the Yaesu MTU filter shape graph, LOOK AT THE FREQUENCY SCALE CLOSELY.
If the MTU preselector is so wide, why is it tunable rather than fixed?
Because the MTU filters, on all but the very narrow 30M band, have enough additional roll-off at band edges (typically 6 db) beyond their insertion loss to be perceptible within the ham band in use. This can be tuned out. If the filter was fixed, the operator would have to live with about twice as much loss at band edges. CW operators, in particular, would not be happy.
Do the MTU preselectors improve signal to noise ratio (SNR)?
Yes, they do. Because much less additive noise and interference is actually making it past them into the active electronics of the receiver. In essence, the receiver noise bandwidth is severely reduced, which reduces noise power into the receiver dramatically, while the signal of interest is reduced in amplitude by just the insertion loss (about 6 db). Note that the NOISE FIGURE of the front end, which is a completely different metric, gets slightly worse, because the signal of interest IS attenuated by insertion loss. To bring it up to its former level would require amplification, which introduces more noise, and this slightly degrades noise figure, which is already quite good in modern receivers. Regardless, in most cases where we have a usable but noise/interference swamped signal, improving the SNR is what “pulls it out of the mud”, with receiver noise figure being a distant second order effect.
So… if MTU insertion loss is only about 6 db, WHY does my S-meter reading drop by 2-3 S-units or more (you’d think this would be about 12-18 db)?
Yaesu S-meter calibration is generally 3 dB per S-unit and does NOT follow the loose “6-dB per S-Unit” meter standard often quoted on-line, so this reflects 6-9 dB of insertion loss in the center of the filter pass-band for the MTUs.
Note that significant out of band noise and interference power can be eliminated by the MTU pre-selectors, depending on band conditions, allowing RF gain to be increased for the key signal(s) of interest within the adjustable MTU pass-band. But even if gain is not increased when using the MTUs, a less noisy signal with a lower S-meter reading and less applied gain can still be much more legible. Skilled operators from days gone by who were used to manual RF gain control knew this very well and used reduced gain as a form of noise reduction.
Why do the MTUs perform better in the lower frequency bands like 160M, 80M and 40M?
160M, 80M and 40M typically have much more background noise and interference than the higher bands, pumping more unwanted power into the receiver front and and (at best) causing desense due to too high an ALC level (to turn down RF front-end amplifier gain) … and … MTU bandwidth is much narrower on the lower bands, making them more effective in limiting noise and interference. The MTU preselectors relatively narrow bandwidth, compared to the receiver’s band-pass filters, lets less noise through, preventing receiver de-sense and preserving dynamic range for the bandwidth of interest. 160M in particular is very noisey - AM BCB interference is just below and lots of man-made and natural noise above that.
Do the MTUs improve receiver dynamic range?
Yes and no. They do not change the dynamic range capability of your receiver at all. But they do limit out of band noise and interference from consuming the dynamic range you do have. In a modern receiver with very good ALC action and wide dynamic range to begin with, expect a modest but real improvement. In receivers with broad front ends, limited dynamic range and limited analog/RF gain/ALC action, the improvement will be more dramatic. Perhaps for this reason, MTU benefits appear to have been more pronounced on earlier Yaesu Tranceivers.
MTU UNIT MEASUREMENTS:
Now, here are a few actual measurements of MTU performance, done with a spectrum analyzer/tracking generator to evaluate -6db bandwidth, insertion loss, in-band roll-off and ultimate band-to band rejection. Both signal source and load impedance were 50 ohms and coax jumper loss and tilt (which was pretty small anyway) was calibrated out before testing. Note that the MTUs have RCA jack RF inputs and outputs.
MTU-160 - Insertion loss at 1.9 MHz: 6.3 db, -6db bandwidth: 45 KHz, Additional attenuation at band edges when centered in mid-band: >17 db, AM BCB attenuation: >28 db, 80M band attenuation : >34 db.
MTU-80/40 on 80M- Insertion loss at 3.75 MHz: 6.2 db, -6db bandwidth: 110 KHz, Additional attenuation at band edges when centered in mid-band: >17 db, 160M band attenuation : >42 db, 60M band attenuation: >29 db.
MTU-80/40 on 40M- Insertion loss at 7.15 MHz: 5 db, -6db bandwidth: 254 KHz, Additional attenuation at band edges when centered in mid-band: >7 db, 60M band attenuation : >30 db, 30M band attenuation: >27 db.
MTU-30/20 on 30M- Insertion loss at 10.125 MHz: 6.1 db, -6db bandwidth: 233 KHz, Additional attenuation at band edges when centered in mid-band: >0.5 db, 40M band attenuation : >36 db, 20M band attenuation: >31 db
MTU-30/20 on 20M- Insertion loss at 14.16 MHz: 6.1 db (not possible to set MTU exactly on band center), -6db bandwidth: 359 KHz, Additional attenuation at band edges when centered in mid-band: >5.1 db, 30M band attenuation : >35 db, 17M band attenuation: >28 db.
As with any amateur review, this is my experience and opinions only, and as I’m not blessed with the divine characteristic of perfection, errors may exist in this write-up. Tests were casually done, out of curiosity, and made available to the community as they might be useful to those considering Yaesu MTU purchase (there is a lot of confusion regarding them). This is not an exacting evaluation, nor does it pretend to be.
Best Regards,
Brian – K6BRN
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