Batboard

What has been the group experience regarding the low end transmit range of the GTX portable? I've tried to get a couple to lock up to 910 on the low-end, with no real capability beyond 905.

Has anyone done any mods on the portable to help this problem?

Rob

What are your RSS settings as read currently?

Here's the settings I have currently programmed into 3 GTX portables, all are 900 radios that transmit on 902 and 927 at 2.76 watts(which is super).

Deviation Balance: 26

Deviation attenuation: 175

Oscillator warp: 78

TX power: 105

Squelch: 7

I adjust squelch from open, to first number that quiets the receiver, then go up one more number.

Always write down your base adjustments to refer back to later, play as needed, fine tune as required.

Deviation should be close to 3 Khz. under the above settings.

Due to the lack of proper heatsinking of the PA modules in these radios, as well as the GP300 series, LTS and so on...keep your output levels on the 'light' side to prevent PA failure, and besides, a less than 1.2dB power loss is NOT going to make or break a conversation, but it will help battery life though.

Even testing a repeater with a yagi at 8' above ground and INSIDE a house with a bare receiver as well, I could EASILY access the machine from 2 miles away and hear it without any difficulty, even though I could not use 927.500 as a talk back frequency, the repeater beats T/A hands down.

From Tempe to Mesa, while driving with the GTX inside the van, I had no trouble getting into this repeater and hearing it as well, but the radios are 900 Mhz. 'Tracs, instead of the converted ones.

TX power was 6 watts out of the duplexer, through 12 feet of *cough* RG58/U cable feeding a Cushcraft 7 element yagi.



Enterprize.....One to beam up!

The units simply go out of lock at anything above 904.8. I have the need to transmit at 908, but, not with these. I have three of them, and, they all stop at exactly the same point.

Rob

I have two H11Ws and one M11W GTX, all with the modified mdf files, and none of
them will work on the "old" 900 mHz band. The radios accept the 919 program
but do nothing when I try to transmit. Looks to me as if the commonly-used
mdf file for 902/928 leaves out the midband, which is fine with me.

And AEC I think your GTX setup info should be made into a "sticky" for the
900 mhz section of the board. I intend to check out all three of my radios to see
how they compare to your setup first chance I get.

Rob:

What version of RSS are you using to program the radios?

You have to have the 'modified' version 4 of the .MDF to allow out of band frequencies to be entered and used by the GTX, older versions such as 1.00.00 or 02.00.02 will NOT work, neither will older versions of lab.

With the modified .MDF file, you can enter your channel data after the read cycle, and program the radio, just write down the tuning data before you program/reprogram, you'll need that 'baseline' information to properly tune the radio.

I have good tuning data for the GTX as I have been playing with the deviation, balance and so forth, and have come up with a good range the radios operate well with, this includes transmitting at 902 and 927.500 for T/A, so you should have NO trouble getting your GTXs to work within the ham bands.

Let me know via Email if I can be of assistance to you, I'd be happy to work with you to get your radios up and running, we need as many on 900 as we can get so we do not lose this to commercial interests, or another Fed-Ex/UPS fiasco that stole our lower portion of 220 from us.

I will also have a peek at the .MDF file to see if there is a correlation with the VCO lock ranges, and radio performance between operating at 902 and 927, maybe there is a 'dead zone' I have never noticed before, I'll program a couple with reverse splits to see if there is indeed a problem area we batlabbers can work around.

Odd splits should not be a problem if the radios transmit at 902 AND 927, but there could be...More research is needed in this regard.


Enterprize.....One to beam up!

So, your GTX portables will transmit at 908-909? Did I read that right?

My RSS takes the data, and the programming takes fine. The receive at 920-921 works (a little deaf) but the 908 TX does nothing at all. I'm using a RSS version just over '4', and, I modified the definition file to allow anything to be entered.

If I program 904.7 I can transmit, if I program 904.8 or higher (until I get to the T/A VCO) it doesn't.

Rob

After programming and testing, I too find that my GTX portables do NOT transmit on either 908, or 909 Mhz.

I programmed these odd splits to test my theory, and proved the theory to be sound.

The radio does NOT like to be operated outside the 902 range, and is also outside the upper range for T/A use, those frequencies are not usable with the current .MDF settings, and in order to get this range to not only program(which it will), but transmit there as well, there will be some toying with the range of the VCO so that a lock is possible.

If operation in this range is needed, I think it would be safe to say that you will lose some upper and lower end band usage due to the 'new' VCO range the radio has been adjusted to.


But dealing with a dual range VCO(which I suspect this radio has) there will be losses in the lower end range, from 902 up to possibly 905 or so, since the band would be shifted upwards this would seem logical.

I'll have to do some more testing on this and see what actual ranges I can work with, and what I will lose in the process, I'm certain there will be band loss over this, I just hope the TX audio or the softpot settings are not affected by this to any degree.

I need to obtain some more service manuals...Grrrr...
I HATE working without a manual!!!!

Like flying without instruments!

I think it is safe to say that the GTX will NOT work on the 900 ham band if you expect to operate outside the 'normal' band split of 25 Mhz.
Although there are repeaters that do not follow this, it is the 'norm' in the western parts of the nation where frequency reuse is in full effect.

Just my personal observations.

The radio will NOT function on 908-915 and work at 902-907, something has to give, unfortunately, the VCO range is what you have to give up to make it happen.

Unfortunately, my needs include both mid-band and band edge (aka 12 and 25 MHz splits) repeater use. Some of the country is still in the 12 MHz, 5 KHz wide camp. No need to debate which is better - some places have one, or the other, and some have both!

I've played with the voltage to try to get the thing to move. I've been operating under the theory the original VCO transmit range was wide enough, so, it should be possible. Using some of the tricks around on the web hasn't produced any results on these models, and neither has falsing the D/A and/or providing the control voltage directly. It is pretty difficult to work on.

I haven't given up, yet, since I have a half dozen of these things.

Rob

The GTX mobile I own has a dual VCO configuration. One is used for simplex transmission. The other is used for repeater transmission and mixing down repeater and simplex transmissions.

One issue is that without changing the IF of the radio, the receive VCO needs to be much wider than originally intended. That vco needs to cover from about 880 (bottom of small split repeater inputs -45 MHz) to the top of the small split outputs. This is significantly wider than the 6 megs that the VCO is originally designed for. Unfortunately both VCO's use the same loop filter.

On a related note the GTX mobile service manual tells which capacitor to change to move the center frequency and which to change for slope.

I have no idea how this transfers to the handheld. Is the handheld a dual VCO architecture?

BigGuy:

Yes, the handhelds are also dual VCO radios, for the same offsets on T/A and standard split.

Due to the design of the radio's VCOs and the method of how they are designed, neither VCO appears to be able to shift enough and be stable enough to operate very far outside its intended band width.

I have not performed andy internal surgery to my portables, and I have to locate a service manual before I will even start tinkering with the VCO.

Only a fool would crack open a radio and begin playing without knowing how things work in the radio, or what the components are designed to do.

Too many golden screwdriver radios lying in the garbage bins I'm betting because of this very mentality.

Without a detailed service manual, component values will be unknown and changing them would probably brick the radio as a result, not what I prefer.

Has anyone had experience with the top frequency transmit capability of
the GTX H11 and M11 radios? I have an M11 that won't do 927.800, though
it's fine at 927.500.

Isn't the service manual available from Motorola any more? Shouldn't cost more than $20 if it is.

I'm surprised that it doesn't operate on one or more particular frequencies. I know the mobile radio has erratic output power on the ham freqs, but that's almost fixable.

Bob M.

kcbooboo wrote:I'm surprised that it doesn't operate on one or more particular frequencies. I know the mobile radio has erratic output power on the ham freqs, but that's almost fixable.

Bob M.

- How is that fixable? I've got many PP & LTR mobiles that won't TX above 927.4125, and our repeater output is 927.5000. Very frustrating for talk-around applications. Any viable solutions?

- trg,