Icom V21AT, W21AT, X21AT Notes

By Dave WB6WKB

Revised October 17, 1998

While the models discussed here are for the most part no longer made by Icom, plenty of them are still around and you can probably find a used one without looking too hard. They have been replaced by later models incorporating many of the same features - as well as many of the same "secret" key sequences. You can also apply some of these techniques to other brands of radios which also allow crossband operation. So, read on and if you can use some of the information below, great!

Have fun and happy hamming!

Extended Receive Unlock

The following information for the W21AT originally came from the now-defunct Amateur Radio Mods Gopher Archive at hamster.business.uwo.ca:70/11/.mods. I do not know who the original author is. This is his procedure on the extended receive unlock for the W21AT:

IC-W21AT Receive only expansion:

1) Turn radio off
2) Press [B]+[#] switch and turn ON radio.
   Release [B] and [#] only when the display shows all functions and
   the radio emits a beep.
3) Go to SET mode and a new function will appear after TONE selection. The
   new function is designed by PL. Set PL to "1"for 1 MHz frqcy. enter,
   to 10 for 10 MHz frqcy. enter and to 100 for 100 MHz frqcy. enter

Note1: This modification does not reset information saved on the CPU.
Note2: Frequency range is  50.0-107.995 MHz FM
                          108.0-135.995 MHz AM (aviation band)
                          136.0-299.900 MHz FM
                                for the VHF portion;
                          300.0-999.900 MHz FM for the UHF portion.
The IC-W21AT is a dual band HT for the 2M and 440 MHz bands. The other models are identical in size and appearance and cover other combinations of bands.
I myself (WB6WKB) have tried the above procedure on an IC-V21AT and an IC-X21AT. The extended receive unlock works on both, although not as well on the V21AT as it does on the other two.

As I briefly mentioned, some of the newer Icom HTs have similar unlock procedures. On the IC-W32A, hold in the Squelch button on the side and the Band button on the front while turning on the radio, then keep them pushed in for at least 5 full seconds. You'll see all of the display segments light up, but no other confirmation that anything happened. Then turn the radio off, then on again normally. Assign the UHF to the left-side tuner, and enjoy your 300-999 MHz coverage [cellular bands blocked].


This dual band model covers the 440 MHz and 1.2 GHz bands, and can also receive 136-174 MHz which includes the 2M band. Unlocking the extended receive gives you:
 50 - 300  MHz ..... from the 2M tuner
300 - 1000 MHz ..... from the 440 tuner
1000- 1310 MHz ..... from the 1.2 GHz tuner

This unlocking gives you a new "PL" function in the SET lineup. A value of 1 allows you to enter a frequency starting with the 1 MHz digit; a value of 100 lets you begin entering with the 100 MHz digit.

You can also select the frequency by using the [f] DSEL function.

Sensitivity will be poor in some frequency ranges. Using an antenna for the proper frequency range may help.


This model covers the 2M and 220 MHz bands. The unlock sequence doesn't seem to do anything to the 2M side, but still gets 136-174 MHz receive there (standard). The 220 side unlocks 215-230 MHz receive. Nothing really earthshaking, unfortunately. Perhaps there are other secret key sequences on this model.

Crossband Repeat

This information also came from the now-defunct Amateur Radio Mods Gopher archive. As before, I do not know who the original author is.

This is a one-way crossband repeat mode. It enables the HT to receive on one band, and retransmit the content to the other band. You can use tone squelch selections, repeater offsets, and many other features available during normal operation.

  1. Select frequencies. Make sure both bands are enabled. You can use memory channels, repeater offsets, tone squelch, etc. The "Main" band will be the transmit side.
  2. Lock the keyboard by pushing [F]+[C] keys. You should see "L" to the right of both frequencies.
  3. Then turn the radio OFF.
  4. (This is the hard part.) Press and hold down [F]+[Moni]+[RPT-M] keys, and, while keeping them pressed, turn the radio ON. You should see a flashing "L" to the right of both frequencies, telling you that the crossband repeat is enabled.
  5. To cancel the crossband repeater mode, just press [F]+[C], which releases the key lock.

The instructions above were written for the W21AT. I have verified it on a V21AT and an X21AT.

This mode is far different from the standard "Whisper Mode" full duplex, which can be enabled using [F]+[RPT-M/wspr], and which requires the battery pack which has the second microphone.

In the Whisper Mode, your radio transmits continuously. In the crossband repeat mode, it only transmits when the squelch on the listening side opens (such as a conversation).

One word of caution! You can't cancel the crossband mode if the listening frequency is in use! You can, however, turn off the radio, but the mode will still be active when you turn it back on!

If you consider that you can use this with the above extended receive option, you get some interesting crosslinking possibilities.

   50 - 300  MHz   to  440-450 MHz
  300 - 1000 MHz   to  144-148 MHz

   50 - 300  MHz   to  1240-1300 MHz *
  300 - 1000 MHz   to  1240-1300 MHz
 1000 - 1310 MHz   to   440-450  MHz

  136 - 174  MHz   to  222-225 MHz
  215 - 230  MHz   to  144-148 MHz

* Some functions, such as offset, PL squelch, etc are
  not available when receiving these frequencies on this model.

I won't say much about the uses this can be put to, but it is extremely important to avoid interference with repeaters and other hams. In fact, remote bases are not welcome on a lot of machines. Going the other way, be very careful about what gets retransmitted. Your HT has no ID'er of its own.

Using Crossband Semi Duplex

The "whisper mode" full duplex, as I mentioned above, requires the battery pack with the second microphone, and it transmits continuously on one band as it listens on the other. This way you can use it like it's a regular telephone.

However! Even if you don't have the special pack, you can do nearly the same thing, with some advantages. Just set up two frequencies, one on each band, and have your friend do the same, only in reverse. Then, just use the PTT button whenever you want to say anything to him and vice-versa. The radio still receives on one band while you transmit on the other!

For example: Suppose WB6WKB and N7JY want to chat in crossband semi duplex. WKB has an Icom V21AT handheld and JY has an IC-901 in his car, equipped with 2 Meters and 222 MHz. WKB arranges to transmit on a 2 Meter simplex frequency to JY, and JY in turn will transmit on low power on 222 MHz back to WKB. Each will listen on the other's transmit frequency. If JY is saying something long winded, WKB can cut in on him on the other frequency to correct him or whatever. This really does work, because N7JY and WB6WKB (that's me) actually did it just that way.

This has advantages. You do not need to be transmitting silence on one frequency while you listen to the other guy talk to you. You only have to key up when you want to talk to him. This saves battery power.

It is also possible for a third person, set up the same as you, to cut in and talk to the other guy; but I doubt that's useful in too many real-world situations.

Decoding an Unknown CTCSS Tone

These Icom models do not have an automatic "find the tone" function like the newer ones, but you can do the same thing manually. Just put it into CTCSS Tone Squelch mode, then put it into SET TONE mode, and slowly turn the selector knob on top. When you come to the right tone, the squelch will open. There is a green light on the front of the HT that is lit whenever there's audio coming in, so you know if the repeater is in use while you do this; also there's the manual open-squelch button you can use just to check.

There are instances where this won't work. If the repeater is linked, and the person talking is coming through from some other repeater, it won't be able to locate the tone. Or it might, but it'll be the one for the repeater the DX is using. Also, I think that some repeaters have filters to keep any PL from the input from going onto the output.

This feature is a good one to have because there are many open repeaters with unpublished CTCSS tones. Often they've been accidentally omitted from repeater directories. Now, sometimes a repeater will announce the tone during the ID but you can't count on that.

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Dave Bartholomew
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