Radio Testing
I often operate on the 2 meter FM band from my car. Recently, I decided to investigate some of the quirks of several of my 2 meter transcievers.
Kenwood TM-281A:
This unit is currently in production. It is a decent performer, although it has a few limitations. It has only a moderately sized heat sink that can get extremely hot, especially when operating at high power (65 watts). Even at low power (25 watts), it still can become very warm if you make a long transmission. If you find yourself wanting to make long transmissions, consider setting the time-out timer in the menu to shut off the transmitter after 3 minutes (or less). This will keep the heat sink a lot cooler.
Another major annoyance of this radio is that it lacks a front panel squelch control. Instead, you have to go into a menu and select the squelch level setting. Level 0 is off; Level 1 for my sample turned out to be equivalent to ~0.2 uV (in noise squelch mode). This is not a bad choice since it aligns closely with the 12 dB SINAD point. However, the squelch does not have any hysteresis, and that makes a weak signal near the squelch threshold fairly unintelligible (because the squelch "chops" the signal badly during fades). This situation can be mitigated somewhat by programming one of mic buttons to turn the squelch on or off so you don't have to dive into the menu to find that function, which is a bad idea while driving.
However, there is an even better solution. Go into the menu and turn on S meter squelch. For my sample, setting it to S1 aligns with about a 0.25 uV input signal. Thus set, the squelch won't open on quite as weak a signal as it will in noise squelch mode. But as it turns out, it works much better on weak and fading signals. That is, if you also set the squelch "hang time" to 250 or 500 msec in the menu. The hang time is only adjustable if the radio is set to use S meter squelch. I missed this point when I first set it up. For general operation you might choose 250 or even 125 msec, but if you want to work weak stations while driving around out in the country, I'd recommend the 500 msec setting. Now the squelch will stay open through brief fades that you might encounter on the road.
Another helpful thing to consider doing is to program one of the microphone buttons to change between low (25W) and high (65W) power. Then you don't have to take your eyes off the road to kick up the power when you need to. Again, this is normally a difficult operation otherwise because you have to push a button and turn a knob to the correct menu item and then adjust it before returning to normal operation (another button push). You can't safely do this while driving (at least, I can't).
In summary: Choose "S meter squelch" in the menu instead of noise squelch and set the squelch "hang" time to 250 or 500 milliseconds. Program one of the mic buttons to change the transmitter output power between low and high power (it will change with each button push-- easy)! Program another one to turn the squelch on and off. With these settings, the Kenwood TM-281 becomes much easier to use on the road.
Yaesu FT-2900R/2980R:
The second radio I tested was a Yaesu FT-2900R. This unit has now been replaced by the FT-2980R, but they are very similar. The only difference that I could identify was that the 2980 can put out 80 watts vs. 75 for the 2900. Both radios have an enormous heat sink that is well suited to dissipating the large amount of heat developed during full power operation. Another good thing about these radios is that they do have a front panel squelch control. Unfortunately, the squelch circuit is very prone to opening on broadband noise that you will often encounter when going past buildings or when a truck passes you on the highway. It is extremely annoying to hear loud noise bursts for hours on end while driving. Also, the squelch seems to lack hysteresis. It has an S meter squelch mode that you can enable, but there is no adjustment for "hang time" like there is on the Kenwood. If you turn on the S meter mode, it works in conjunction with the noise squelch such that the most restrictive setting "wins". As with the Kenwood, you can set the S meter squelch threshold. I found that the lowest setting corresponds to ~.355 uV on my sample. However, the S meter squelch is useless for preventing those noise bursts from breaking through, because noise levels of S9 or more are frequently encountered while driving and you don't want to set the threshold so high that you effectively have a "wooden" receiver. What to do? I don't use the S meter squelch function on this radio because it's ineffective at stopping the noise bursts and because it limits weak signal reception. After further testing, I discovered that I was probably setting the squelch threshold too low in noise squelch mode. Even if the squelch control is set fully clockwise, only about a 0.355 uV signal is required to open the squelch. I found that a squelch setting of between 1-3 o'clock eliminated a large percentage of those annoying noise bursts while still allowing most weak signals to come through. For working really weak stations, I find that I have to turn off the squelch. You can either reach down and turn the control, or else program a microphone button to do it for you (the "monitor" function). I am not a fan of the way the Yaesu squelch circuit works, but as they say, it is what it is. An ambitious person could probably modify the squelch noise filter to make it more effective, but I didn't see an easy way to add hysteresis. The output of the squelch noise detector directly feeds a pin on the microprocessor chip.
ICOM 2300H:
I found this radio super easy to program. In no time at all, I successfully programmed a half dozen simplex channels and about 30 repeaters into the memories. The power output is adjustable over four levels and it's easy to change from the front panel. The squelch can be programmed to operate in any of several ways. I recommend choosing the option where up to 20 dB of attenuation is available when you turn the squelch knob clockwise beyond the 12 o'clock position. The squelch on this radio is extremely sensitive and it is also friendly to weak and fading signals. It takes about 0.2 uV to open the squelch at threshold but it will hold open until the signal drops below 0.125 uV. It seems fairly immune to opening on broadband noise (unlike the Yaesu FT-2900/FT-2980R). It works just the way you want. Given the relatively small heat sink, if you want to operate at the highest power output, consider limiting the length of your transmissions. The radio has some ability to mitigate excessive heat buildup by limiting the power automatically. You can also set the transmitter to time out when a predetermined period of time has passed. This would be a good idea if you tend to be long-winded. Also consider setting the output power no higher than 25 watts for general operation and only increasing it to full power when needed. Of the three radios that I tested, this is my personal favorite.
Kenwood TM-281A:
This unit is currently in production. It is a decent performer, although it has a few limitations. It has only a moderately sized heat sink that can get extremely hot, especially when operating at high power (65 watts). Even at low power (25 watts), it still can become very warm if you make a long transmission. If you find yourself wanting to make long transmissions, consider setting the time-out timer in the menu to shut off the transmitter after 3 minutes (or less). This will keep the heat sink a lot cooler.
Another major annoyance of this radio is that it lacks a front panel squelch control. Instead, you have to go into a menu and select the squelch level setting. Level 0 is off; Level 1 for my sample turned out to be equivalent to ~0.2 uV (in noise squelch mode). This is not a bad choice since it aligns closely with the 12 dB SINAD point. However, the squelch does not have any hysteresis, and that makes a weak signal near the squelch threshold fairly unintelligible (because the squelch "chops" the signal badly during fades). This situation can be mitigated somewhat by programming one of mic buttons to turn the squelch on or off so you don't have to dive into the menu to find that function, which is a bad idea while driving.
However, there is an even better solution. Go into the menu and turn on S meter squelch. For my sample, setting it to S1 aligns with about a 0.25 uV input signal. Thus set, the squelch won't open on quite as weak a signal as it will in noise squelch mode. But as it turns out, it works much better on weak and fading signals. That is, if you also set the squelch "hang time" to 250 or 500 msec in the menu. The hang time is only adjustable if the radio is set to use S meter squelch. I missed this point when I first set it up. For general operation you might choose 250 or even 125 msec, but if you want to work weak stations while driving around out in the country, I'd recommend the 500 msec setting. Now the squelch will stay open through brief fades that you might encounter on the road.
Another helpful thing to consider doing is to program one of the microphone buttons to change between low (25W) and high (65W) power. Then you don't have to take your eyes off the road to kick up the power when you need to. Again, this is normally a difficult operation otherwise because you have to push a button and turn a knob to the correct menu item and then adjust it before returning to normal operation (another button push). You can't safely do this while driving (at least, I can't).
In summary: Choose "S meter squelch" in the menu instead of noise squelch and set the squelch "hang" time to 250 or 500 milliseconds. Program one of the mic buttons to change the transmitter output power between low and high power (it will change with each button push-- easy)! Program another one to turn the squelch on and off. With these settings, the Kenwood TM-281 becomes much easier to use on the road.
Yaesu FT-2900R/2980R:
The second radio I tested was a Yaesu FT-2900R. This unit has now been replaced by the FT-2980R, but they are very similar. The only difference that I could identify was that the 2980 can put out 80 watts vs. 75 for the 2900. Both radios have an enormous heat sink that is well suited to dissipating the large amount of heat developed during full power operation. Another good thing about these radios is that they do have a front panel squelch control. Unfortunately, the squelch circuit is very prone to opening on broadband noise that you will often encounter when going past buildings or when a truck passes you on the highway. It is extremely annoying to hear loud noise bursts for hours on end while driving. Also, the squelch seems to lack hysteresis. It has an S meter squelch mode that you can enable, but there is no adjustment for "hang time" like there is on the Kenwood. If you turn on the S meter mode, it works in conjunction with the noise squelch such that the most restrictive setting "wins". As with the Kenwood, you can set the S meter squelch threshold. I found that the lowest setting corresponds to ~.355 uV on my sample. However, the S meter squelch is useless for preventing those noise bursts from breaking through, because noise levels of S9 or more are frequently encountered while driving and you don't want to set the threshold so high that you effectively have a "wooden" receiver. What to do? I don't use the S meter squelch function on this radio because it's ineffective at stopping the noise bursts and because it limits weak signal reception. After further testing, I discovered that I was probably setting the squelch threshold too low in noise squelch mode. Even if the squelch control is set fully clockwise, only about a 0.355 uV signal is required to open the squelch. I found that a squelch setting of between 1-3 o'clock eliminated a large percentage of those annoying noise bursts while still allowing most weak signals to come through. For working really weak stations, I find that I have to turn off the squelch. You can either reach down and turn the control, or else program a microphone button to do it for you (the "monitor" function). I am not a fan of the way the Yaesu squelch circuit works, but as they say, it is what it is. An ambitious person could probably modify the squelch noise filter to make it more effective, but I didn't see an easy way to add hysteresis. The output of the squelch noise detector directly feeds a pin on the microprocessor chip.
ICOM 2300H:
I found this radio super easy to program. In no time at all, I successfully programmed a half dozen simplex channels and about 30 repeaters into the memories. The power output is adjustable over four levels and it's easy to change from the front panel. The squelch can be programmed to operate in any of several ways. I recommend choosing the option where up to 20 dB of attenuation is available when you turn the squelch knob clockwise beyond the 12 o'clock position. The squelch on this radio is extremely sensitive and it is also friendly to weak and fading signals. It takes about 0.2 uV to open the squelch at threshold but it will hold open until the signal drops below 0.125 uV. It seems fairly immune to opening on broadband noise (unlike the Yaesu FT-2900/FT-2980R). It works just the way you want. Given the relatively small heat sink, if you want to operate at the highest power output, consider limiting the length of your transmissions. The radio has some ability to mitigate excessive heat buildup by limiting the power automatically. You can also set the transmitter to time out when a predetermined period of time has passed. This would be a good idea if you tend to be long-winded. Also consider setting the output power no higher than 25 watts for general operation and only increasing it to full power when needed. Of the three radios that I tested, this is my personal favorite.