This might be a better question for ham radio groups, but what is currently a good VHF mixer to use for good large signal handling? Leaking/radiation and power draw is a concern as well so i'd like to avoid SD/FST and similar beasts (that might not work that high anyway).
Did anyone experiment with modern car radio ics? Some have image-cancelling mixers, I wonder how these perform in large-signal environment.
Mark
The car radio ics are made for quick and cheap designs. They all work badly in a high signal environment.
Mixers are nonlinear devices, if they were not, they would not work. Thus to make them work well with large interferring signals, it is necessary to have them use large level signals. The double balanced mixers from Minicircuits are about the best you are going to do without a huge amount of work. They are cheap and work well. The downside is that they do not fit in the low leakage and power domain (depending on what you mean by low power).
I have designed radios for high rf environments like Mt Wilson in LA and the diode mixers were the best performing choice there.
I second the recommendation for Mini-Circuits. If a high level (+13 dBm LO) diode DBM won't do it, you're into the MOSFET bridge realm, which is tougher to do.
(An ideal mixer is a perfect analog multiplier, which is bilinear--i.e. it satisfies linearity and superposition at two separate inputs simultaneously--rather than nonlinear. We've had threads about this in the past.)
Cheers,
Phil Hobbs
Of course, practical DBMs are not intended to be linear with respect to LO input, but they certainly are with respect to the other two ports. -- But isn't saying "...satisfies linearity and superposition..." redundant, since superposition is one of the requirements of linearity?
Cheers, Tom
Could you be more explicit about the frequency, the desired IP3, and just what sort of port isolation and drive power requirements you're looking for?
You can trade off LO drive power for power to run the mixer: that is, diode DBMs require significant LO power (and more for higher IP3, in general), but active mixer circuits will instead require DC power while running on low LO power. You'll have a hard time finding active mixers that perform as well as diode DBMs, but check out Analog Devices, Hittite, Linear Technology, and undoubtedly others for some active mixers that will perform a whole lot better than the mixer employed in car radios, which pretty much invariably use highly integrated ICs these days, designed to meet a price point. MOSFET switch versions of DBMs (e.g., H-mode mixers) are really good at HF, but AFAIK you can probably do better in the upper reaches of VHF with diode mixers, especially ones designed for higher LO power.
If you're willing to add "tweaks," you can null the LO feedthrough of a (diode--or other) DBM. This will be easiest to do at a single frequency or over a narrow band, of course, and will likely be temperature sensitive.
You mentioned image-rejection mixers (e.g. quadrature mixers). Do you need that, too? You didn't mention that as a requirement or even that it might be desirable...only that some "car radio ics" have them.
Cheers, Tom
Have you looked at a Tayloe Mixer?
The device discussed in this article is a detector and preamplifier. Its features are based on an extremely compact and simple design compared to other zero IF I/Q quadrature detectors. The device's feature set includes:
a.. Less than 1 dB of conversion loss, b.. ?Free? tracking bandpass selectivity (Q = 3,500 at 7 MHz), with a user definable bandwidth, and c.. A high third-order intercept (+30 dBm). The product detector's upper frequency limit is set by the ability of a field effect transistor (FET) to be turned on for only a quarter cycle of the incoming RF signal being converted to baseband. The maximum useful frequency for this detector readily extends to at least 10 GHz.
The companion I/Q quadrature upconverter is simple and allows the conversion of baseband quadrature signals to RF with negligible conversion loss.
Robert H.
Yes, I meant time-invariance and linearity. My bad.
I agree that diode DBMs aren't linear in the LO, but that's part of the reason for all the spurs they generate. Analogue multipliers generate much lower spurs, within their frequency ranges.
Cheers,
Phil Hobbs
Similar to 2m band, well, it will be often mounted on high locations, with other gear and open to all kinds of strong signals you can imagine. I have now decided to use good tunable filter in RF front to relax these requirements a bit so maybe the next best thing to diode mixer would work here. I'll check AD goodies, 24-25dBm would possibly do it, I guess I'll have to live with high power consumption.
Yes, my first thought would be "cheap" and "bad", however FM bands are full of strong close-by signals and I thought maybe the capable guys at nxp came up with a good solution. These tuners have lots of goodies and simplify design, however I see your point, too, of course.
I did look at H mixers, they don't look very convenient for manufacuring.
I need to cover a wider range and I don't like "tweaks" in production. Heavy shielding is also best avoided, where possible.
Well, it simplifies front-end filtering somewhat as the image is attenuated some 30dB, that's the only reason. I'll probably settle for a bit more complex tunable bandpass.
Mark
In any case, your lowest power, most bulletproof addition is a good front end filter. Stuff that does not get in cannot hurt you. We had receivers sharing a tower with kw transmitters 20MHz away and the filters did a good job. You can calculate what you need by looking at your sites with a spectrum analyzer and then seeing what the response of your front end is. A good interdigital filter is easy to make and works extremely well.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.