The P25.IO team will post about modifications and repair related to older Astro, Astro25 and Quantar P25 equipment. This is a place to provide information to the P25 community and to prevent good information from being lost. If you have something to contribute, feel free to contact us.



Analog Quantar Linking Using Cisco E&M Cards

Many people are using Cisco routers for P25 linking via the serial WIC cards. If your router can deal with voice hardware, then it is possible to use E&M cards to link with other mixed mode Quantars or analog repeaters, using the same router.

This PDF from Cisco gives you an overview about the necessary hardware, in short you need a router that can accept voice hardware, then depending on the router either a voice network module or a DSP module and a VIC E&M card. Also make sure that the IOS feature set running on the router can do both voice (LMR) and STUN. We use 2600XM series, 2801 and 2811 for example. E&M Type II interface model is used in our case, if you look at the E&M cards RJ45,  pin 1 is  left and pin 8 right, the TX and RX Audio pins 6&3 and 5&4 are connected to the Quantars orange analog audio connector at the back. PTT  is connected to the 50 pin Telco connector, E&M pin 8 goes to 7 on the Telco and E&M pin 7 is connected to 11 (AUX 1) on the Telco. E&M 1&2 are not used, we use VAD Ciscos voice activity detection. On the Quantar we need to configure a wildcard, first define AUX 1 to be active low, and then set up a wildcard entry that keys from WL when AUX 1 is low (active). This is only to show what is needed to pass analog wire line audio to the transmitter, you can setup more wildcard tables so that analog and digital not interfere. A little bit creativity is needed here to find the best solution for your needs. If you are using a Astro-TAC 3000 for mixed mode linking, then you don’t need the PTT cable and wildcard entry, the station will be keyed via the V.24 interface, even for analog transmissions.



I assume that  your router has networking configured and you can reach the distant router. Firs add this voice class to the configuration:

voice class permanent 1
signal timing oos timeout disabled
signal keepalive disabled
signal sequence oos no-action

Then apply this connfiguration to each voice port:

voice-class permanent 1
operation 4-wire
type 2
signal lmr
bootup e-lead off
lmr e-lead voice
lmr duplex half
lmr led-on
input gain 3
output attenuation -3
no echo-cancel enable
no comfort-noise
timeouts call-disconnect 3
timeouts wait-release 3
connection trunk 100
description E/M Voice Port 0

The bootup e-lead off and lmr led-on will not work on the 2600XM series, leave it out, it will work just fine, the downside is that the repeater or transceiver will be keyed up during the routers boot period.

If you are using a comparator or voter that needs guard tones, then use lmr duplex full, input and output levels are exaples, you may have to adjust them to fit your needs. Next  create the necessary dial peers first on router 1:

dial-peer voice 100 voip
description -your description here-
destination-pattern 100
session target ipv4: R2 IP
codec g711ulaw
ip qos dscp 5 media
ip qos dscp 5 signaling
vad aggressive

dial-peer voice 101 pots
destination-pattern 101
port 1/0/0

And this needs to be configured on router 2:

dial-peer voice 101 voip
description -your description here-
destination-pattern 101
session target ipv4: R1 IP
codec g711ulaw
ip qos dscp 5 media
ip qos dscp 5 signaling
vad aggressive

dial-peer voice 100 pots
destination-pattern 100
port 1/0/0

You can see how the 100/101 interrelate on both routers, so if you use the second voice port, you can configure more dial peers using 102/103 and port 1/0/1 insted of 1/0/0. The destination-pattern numbers are not important you can use everything as long as you have a matching pair. This setup is a one to one thing, perfectly fine if you use is with a voter or if you only need one link to a distant location. It is also possible to use Multicast, this way you can have multiple destinations and also tie in Cisco phones or listen in via PC for example. I will add Multi cast info as soon as possible.

Quantar V.24 Interface Board

We have taken the idea of a cheap and easy to obtain V.24 interface board one step further. The board size was chosen to stay just under 25 cm² to be within the limit of the lowest price option from many cheap PCB manufactures. A RJ45 socked is used to have a easy to obtain connector, same pin-out as on the original board of course. The relay as part of the clock in/out selection is not needed if a Cisco router is used, in this case a fixed clock in configuration would work just fine, but to encourage experimentation and also support in cabinet connections to a Astro-Tac comparator for example, the necessary components are there.

The project is open source, all necessary files can be downloaded here

V.24 PCB

Known issues / planed improvements

  • PCB version that utilize the internal + – 9,6 V ?

A big thank you to all the fellow P25 enthusiasts that did an amazing job on reverse engineering the protocol used by the Quantar and made Quantar linking via IP a real thing. Also thank you to the p25.ca user kayfox, he published the first version of a V.24 replacement board.

Quantar TTN4094 SCM NO Modulation Repair

U306If your repeater keys up without modulation or very low modulation, either in P25 or analog, it might be because U306 on your SCM is dead. This seems to be a common fault on the TTN4094 board, I have heard about this issue from a lot of P25 enthusiasts and had this issue more then once myself. U306 are MAX292EWE a 8th-order lowpass switched capacitor filter, they are part of the audio processing, you can find the data sheet here. To verify that U306 is dead you can scope the input pin 14 where you should see a signal then scope output pin 11, if there is no signal or a signal which is orders of magnitude smaller then the input, replace U306.


Quantar Onan Power Supply Repair

A while back one of mine low power Onan power supplies failed, but I was able to figured it out and bring it back into operation. From what I read on the net, it seems that the Onan’s don’t have the best reputation, so I will share my experience to help you guys bring them back to work.

I noticed an odd ticking sound coming from the power supply, before I could turned it off, a big bang and some smoke came from it and of course it was no longer working. Time to bring it on the work bench and drill out the rivets. It seems that there is no service manual or schematics available for these supplies, but to get a clue on how the thing works I used the theory of operation section in the Quantar instruction manual. The Onan supplies seems to follow the same design, mains power is rectified after that there is a PFC / SMPS boost circuitry with bring the voltage up to 400V DC regardless of the input voltage. The 400V handled over to the DC -DC converter with gives us the output voltages. It was obviously that the two 270uF caps exploded, so I began looking at the boost circuit and did some measurements and noticed that the 400V are way off, was well over 500V, no wonder that the 450V rated caps let some smoke out. The boost circuit is build around an ML4812, same as in the Motorola supplies, hence I used a schematic from one of these to get a better understanding. I found four dodgy resistors, one open the others increased their resistance. After changing the caps and the resistors, the 400V where spot on, same with the output voltages.

After you drill out the two rivets on the side, remove the front plate and the screw next to the power switch, you can now carefully remove the back plate, disconnect the fan and slide the PCB out of the case. Disassemble the PCB from the heat-sink. If you have the PCB in front of you, on the right side you should see the four resistors.


Don’t trust them only because they look Ok, mine looked fine but all of them were defect.


On the back side of the board notice the brown color, lot of heat was there. On my unit the mains cable going to the switch in the front was laying directly on these resistors, no airflow for cooling, the constant overheating is presumably the cause of the problem.


I haven’t mounted the new resistors flat on the board, so they have a better cooling, also routed the mains cable different. After the repair I found that the resistors not running hot any longer.


From what I see, this could happen on the high power version as well, it seems that on the high voltage board the only difference is the lack of 3 caps and two MOSFETs on the 400V boost circuit.

The defective parts where:

4x 200 KOhm resistors
2x 270uF electrolytic capacitors (5x in the high power)

I could’t find any info on the net about repairing this exploded “fireball” Onan power supplies, if you have discovered other faults, it would be appreciated if you also contribute your experience and leave a comment.

Quantar Exciter Repair

I repaired a few Quantar repeater with broken exciters. The fault condition is most of the time the same. If you power the Quantar up, all lights come up green and when you key up the repeater the red PA Fault LED turns on immediately. However I also heard reports of an more intermittent fault whit power changing from high to low. I was told that early Firmware on the exciter can cause the same behavior, so keep this in mind. With a known working exciter the station works with no problems whatsoever.

On the status report screen the station gives you the error messages shown in the picture below, no TX forward Power and bad internal SWR.

Status Screen

So time to dig out the big service manual and open up the bad exciter. It looks like the Quantar have seen some moisture due to humidity, in the region of the front LEDs is some corrosion, all solder joints are looking dodgy:





If you have the open exciter lay in front of you the LEDs on the left side, then you will notice two black chip resistors an above you will see a capacitor and an inductor, right hand you will see the final MMIC labeled with A03. The two resistor are the bias resistors for the MMIC, the inductor is an RF choke so the MMIC output don’t see the bias resistors. Nothing fancy going on here.


This is the part of the circuit that we are interested in, L3106, C3109 and U3100. I also checked R3108 and R3109 they where ok in all units that where on my bench, but please check them just to be 100% sure that they are ok.


I found out that the isolation of the inductor was completely gone and the wire went open circuit. If you in luck than this is the only fault you have to deal with, change the inductor check the cap besides and if necessary change it. But unfortunately I had some exciters with not only a broken inductor, the MMIC let the magic smoke out and went bad. In this case you have to change the MMIC, at least where I life the original Motorola part is absolutely unobtainable, so I designed another 50 Ohm MMIC in without any problems.



All Quantars are back in service and running perfect without any errors.

Status OKGreen


The discussion on an forum came to the conclusion that the black foam behind the vent holes had a low impedance, this in combination with extreme humidity is very likely the cause of the problem. In my opinion we could remove the foam without any negative impact on the performance. After repairing and especially after changing the MMIC, I highly recommend a realignment of the Quantar, only a aligned  Quantar is a happy Quantar. If you are working on the repeater it is also a good idea update the firmware to the latest version. There will be a separate article on how to do this.

The parts needed for the repair are:

  • L3106 – 220nH +/- 5% SMD case 1008
  • C3109 – 100pF +/- 5% 50V SMD case 0805
  • U3100 – MMIC 50 Ohm 12dB Motorola part nummer: 4882347W01 (MWA0311T1)

I could not get hands on a original MMIC so i decided to build in a MSA1105 that I had. So I hope this will help somebody, if you have any questions feel free to leave a comment or contact us.