MAXAR50/HT440/HT90/MOXY/MT500/MX300 Series


This radio is not software programmable. The PL tone can be changed as per the instructions in the manual.

The pinout of the mic connector is:

1------Spkr hi
3------mic audio
5------mic gnd
6------PL disable (shorted to gnd enables PL)


The HT-440 is nothing more than an HT-90 in a fancy case. It is strictly a crystal type radio and therefore not programmable (even the PL or DPL boards take physical "reeds"). It is, however, a good radio and will generally exceed rated wattage by about 40%. They will go pretty far out of band just by putting in the right xtals + realigning.

Being a rock radio, 1 pair of crystals (Rx and Tx) are needed for each channel. The radio is fitted with either a 2 pole c/o switch for the 2 ch. model or a 4 pole 4 pos. rotary for the 4 ch. version. It is to all intents and purposes an HT 90 radio (same circuit board) but a darker coloured case. The same batteries fit but look odd because of the different colours. This radio exhibited very few vices in service, the 2nd local osc. crystal would give up occasionally and the P.L. element would fall out of its socket on the piggyback tone board. The on/off switch contacts can go high resistance causing some funny symptoms but usually a quick burnish with a relay contact or automotive type points file would sort them out. The battery contacts between the case and the circuit board need to be kept clean (they are tightened by the two screws through the top plate).

The formulae for calculating the crystal frequencies are as follows:

As for the receiver second oscillator frequencies, they depend on what the frequency of the first oscillator is, and they are:


Carrier Frequency
First Oscillator Frequency
Second Oscillator Frequency
403.0-409.0 53.05-53.8 20.945
409.0-413.75 53.8-54.39375 21.855
413.75-417-75 54.39375-54.89375 20.945
417.75-427.0 54.89375-56.05 21.855
427.0-430.0 56.05-56.425 20.945
440.00-448.30 52.3250-53.3625 21.855
448.30-456.25 53.3625-54.3563 20.945
456.25-457.42 54.3563-54.5025 21.855
457.42-460.32 54.5025-54.8650 20.945
460.32-473.50 54.8650-56.5125 21.855
473.50-476.30 56.5125-56.8625 20.945
476.30-486.35 56.8625-58.1188 21.855
486.35-493.10 58.1188-58.9625 20.945
493.10-501.25 58.9625-59.9813 21.855
501.25-512.00 59.9813-61.3250 20.945


Carrier Frequency
First Oscillator Frequency
Second Oscillator Frequency
136.00-138.00 39.3667-40.0333 17.445
138.00-140.48 40.0333-40.8600 18.355
140.48-148.00 40.8600-43.3667 17.445
148.00-154.80 43.3667-45.6333 18.355
154.80-157.00 45.6333-46.3667 17.445
157.00-164.28 46.3667-48.7933 18.355
164.28-171.70 48.7933-51.2667 17.445
171.70-174.00 51.2667-52.0333 18.355

The VHF transmitter uses an oscillator stage followed by two tripler stages to get the 9 times multiplication of the crystal frequency. The UHF transmitter uses an oscillator stage followed by three tripler stages to get the required 27 times multiplication of the crystal frequency. Theoretically the crystal's for VHF and UHF should be quite close in their fundementals and you could use a VHF crystal in a UHF radio for testing and it should oscillate (ie. a 16.26MHz crystal for 146.340MHz should give you 439.020MHz in a UHF radio).

The following are the part numbers and frequency ranges for the VHF boards:

Part Number Frequency (MHz) Power (W)
NUD6421B 136.000-150.799 2
NUD6422B 150.800-161.999 2
NUD6423B 162.000-174.000 2
NUD6431B 136.000-150.799 5
NUD6432B 150.800-161.999 5
NUD6433B 162.000-174.000 5
NUD6682B 150.800-161.999 5

You can find the pinout of the microphone connector here.

Below is the pinout information of a HT90 speaker microphone:

Universal connector, 4-Contact female #0905184J01

Pin 3  Black wire        Ground
Pin 2  Blue wire         Spk Audio from audio pwr amp thru the J202 ext spk jack
Pin 5  Gray wire         Spk Audio to J401/LS401 Internal Speaker
Pin 4  Blue/White wire   For External PTT Switch (ground to key)
Pin 1  White Wire        External Microphone Audio input.

Pins 2 and 5 make up a N.C. switch that opens when a male connector is inserted, disconnecting the internal spkr.

The manual part numbers are as follows:

The UHF Models come in 2 bandsplits, 403-430 MHz and 440-512 MHz. A model chart for this series should look something like:

H 2 4 HMB 1 124A
H Handheld 2 1W 3 VHF HMB Model Series 1 Carrier Sq. 124A Same for all
3 4W UHF 4 UHF HMU 3 Tone PL
3 5W VHF 6 Digital PL

Handie-Talkie RF Link

Motorola made what they called a "Handie-Talkie RF Link". One model number was K24LCF1103BP.

It is a metal gasketed box, that contains a small Celwave duplexer, two HT440's, a power supply and a controller, 1 per radio.

It appears it was available in both VHF and UHF. The second and third digits of the model number determine bandsplit and power level, as follows:

The UHF models were available in either 403-480MHz or 440-512MHz. They are crystal controlled.

The jumper configuration of the interface board is as follows:

Function JU1 JU2 JU3 JU4 JU5
Low Impedence Line Level Output IN
High Impedence Line Level Output OUT
PTT Low to Key IN OUT
PTT High to Key OUT IN
Unsqu. Ind. High with Carrier IN OUT
Unsqu. Ind. Low with Carrier OUT IN

The factory defaults are: High Impedence Line Level Output, Low to Key, and Unsquelched Indicator High with Carrier.

You can see a schematic of the interface board by looking here.

The schematic for the function board containing the power supply and other circuits can be found here.

The manual part numbers are:


The pinout of the power connector is below, a picture can be found here.

A------12v +
B------gnd (12v -)
1------hang up box
2------hang up box gnd
3------horn out (for horn blower decoder)
5------mic hi
7------switched A+
9------int Spkr
10-----meter point 1
11-----meter point 5
12-----RX audio
13-----meter point 2
14-----meter point 3
15-----meter point 7

The meter points are for an adapter cable to use with a Motorola test set.

MAXAR/MOXY 6M Conversion

We've been told that there is a book available for putting the low band Moxy or Maxar onto 6 Meters.  It is by William I. Oglivie (VE7MIT) and is available from Zen-In Design, P.O. Box 390700, Mountain View, Ca.  94039. 


If you need channel elements for these radios, check out this site

For further extensive coverage of this model, you should check out MT500.COM.

MX300 Series

Again, most of these are non-synthesized radios (use crystals).

The pinout of the microphone connector can be found here.


For all the information you could ever want on the HT220, check out