Why do most HTs have 2m and 70cm as the two bands? Is it just out of history or tradition, licensing restrictions, or is there something in the transceiver or antenna design that would make these the two obvious frequency bands of choice?
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3 Answers
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Worthy of mention is that 432MHz is a harmonic of 144MHz, meaning that the antenna can be much simpler; if it's (electrically) an odd number of half-waves on 2m, it's also an odd number of half-waves on 432MHz.
answered May 14, 2018 at 1:10
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1$\begingroup$ Oh this is good! Didn't realize that relationship had such a practical effect. $\endgroup$– davidbakCommented May 14, 2018 at 2:22
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1$\begingroup$ Circuit-wise too, Scott. Same reason that the HF bands are harmonically related. Back in the day, frequency multiplier circuits were used extensively. $\endgroup$ Commented May 14, 2018 at 3:05
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1$\begingroup$ Yes, of course. Another reason why 40m antennas are some of the most commonly-sold, as they can also be used on 15m (3 x 7.000-7.200 works well on 21.000-21.450) $\endgroup$– Scott Earle ♦Commented May 14, 2018 at 3:16
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3$\begingroup$ @MikeWaters that and it made it more likely that if a ham was putting out harmonics it would only bother other hams. Long ago, 5m and 2.5m bands even occupied their natural places between 10m and 1.25m (but eventually they morphed into 6m and 2m instead). $\endgroup$ Commented May 14, 2018 at 6:59
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$\begingroup$ Note that 440mhz is not an exact 3rd harmonic of 146mhz but it's very close, which means that your antenna has to have a bit of extra bandwidth for it to work on both bands. Luckily, this isn't hard. $\endgroup$ Commented May 17, 2018 at 11:18
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History and tradition are good choices of words, yes. Historically, they have been the most popular bands for mobile work; the antennas are small enough for a vehicle and many repeaters have been constructed for that reason.
6 meters used to be a popular mobile band back in the 50s and 60s. (For that matter, so were 80 and even 160.) All those bands required a larger antenna, and back in those days many hams made their own. And since 2m and 440 were so popular, 220 never caught on except in some terrestrial and EME circles.
answered May 13, 2018 at 22:53
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1$\begingroup$ 80 for a mobile band? How did that work, antenna-wise? (I remember a Field Day where the club I belonged to took advantage of a loophole and strung a full size 80m quad between two really tall telephone poles on our site on the top of a hill. We were "mobile" but you know, not really mobile.) $\endgroup$– davidbakCommented May 14, 2018 at 2:24
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1$\begingroup$ @davidbak Loaded verticals. Same as for 160m, which BTW have about a 1% efficiency on a truck (according to W8JI. :-) $\endgroup$ Commented May 14, 2018 at 15:17
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1$\begingroup$ How do long wavelengths work as mobile bands? The HF equivalent of the rubber duck -- broadside helical. Modern commercial examples are the hamstick, iron horse, superantenna. $\endgroup$ Commented May 17, 2018 at 11:20
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One reason 1.25m / 220MHz is not too popular is that not many other countries than the US have allocations in it, just like we (the US) do not have the 4m band.
Other reasons including what was previously said, could be size/practicality of antennas and useful RF distance. 6m has better propagation and bigger antennas, 23cm smaller antenna/more manageable but quite a bit line of sight propagation. Everything is a trade off in RF.
Virtually any HF antenna on a mobile is a compromised antenna by using coils to make it electrically longer than it physically is, which reduces its effectiveness, but there are those that do it because they can.
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1$\begingroup$ United Parcel Service bought some of that band from the US Government. IIRC, UPS never even used it. Did that affect the amateur use of 220? $\endgroup$ Commented May 14, 2018 at 15:13