Need help with Fontek FM-4016H 2M transceiver conversion (160-171 to 144-146)Mhz

Thank you for the advice. Since the lid of the radio is closed already, further mod will wait until the next time it is opened . Ill try to make the quick RX work first. Maybe make the GDO2 to have additional test instrument.

Thanks and BR,

Noli - 4G1ZYS

Try programming 170.000 MHz, but inject your generator at 127.4MHz (170MHz - 2x IF).

If you say it is "locked" to that range then there could be software restricting the synth. Is there a processor onboard?
If not then it could simply be a case of adjusting the VCO to cover the correct range.

If you have access to the loop-voltage (the DC correction from the loop filter to the VCO) then you will see that voltage vary depending on the frequency to which the synth is locked. You can lock it at, say 160MHz, then tune the VCO so that it stays in lock, but the loop voltage rises from 1/2 supply to about 66% of supply volts. Then you should be able to tune the synth lower thant he bottom limit, if there is no software resricting it.

BR Harry

Hi Harry,

I have tested this radio with possible combinations like high side LO but it seems to locked at 160 to 171. Trying even 171.100 wil not work. There is a video of the mod now. Will post a link soon.

Edit:

Added the video here



Thanks and 73s,

Noli - 4G1ZYS

Hi Noli,
I used to work for PYE Telecom in Cambridge and I did a lot of mods for VHF PMR to 2M (and 70cms) bands. Many times you can simply tune the RF front end to the ham-bands and instead of having the LO low, you have it high. That way you do not need to touch the LO chain/multipliers/synthesiser.

BR Harry

Hi Harry,

Thank you for this information. I think in this radio, the RX LO is 21.6MHz lower than TX. This is how I compute for the N and A of the PLL chip when programming.

I still do not intend to transmit yet since it is outside the amateur band. Another thing, a tantalum cap is removed from the final stage because it is already shorted. I have to replace it first before attempting to transmit (after pulling the frequency to the HAM band)

Thanks and Best Regards,

Noli - 4G1ZYS

n0th1n6 wrote:
About TX/RX, is there a difference when setting the synth frequency for TX and RX? 

Hi Noli,
Yes, there is a 21.4MHz difference between TX and RX.

In the loop filter there should be two circuits:
1 - TX delay of a few ms to prevent TX before the synth is settled
2 - Loop "speed-up" circuit to increase lock-time with large changes of frequency

If the RX LO is 21.4MHz lower than the RX requency, then the synth frequency will have to move up 21.4Mhz when you press the PTT. It is for this reason that you need the two circuits.
Some manufacturers have overcome this problem by having two synthesisers, but this also introduces other problems.

If you have a PTT signal sent to the EPROM address then you have the more normal method.

You could google for some of the older Tait (New Zealand) mobile radios (eg. T500 series) to get a good idea about the design. They used an MC145152-2 synthesiser. Same chip but parallel load instead of serial load (faster). If you cannot find circuits then let me know and I will see if I can find a scan of one. These manuals were very descriptive in the operation and give loads of good educational information.

Very best regards from Harry - SM0VPO

Admin wrote:Hello Noli
Very interesting. From the picture you provide I can see that the RX is a simple superhet, but not the frequency on the filter. 10.7 pr 21.4MHz is most probable.

BR Harry

Hi Harry,

I am not sure about the filter. The markings says 21.600 but the part number says center frequency is 21.4 Mhz. Using an atmega 328, I am able to program the synth to receive on my desired frequency. 

Here is how I do it.

N = (Fout - IF) / channelSpacing / refDivider
A = (Fout - IF) / channelSpacing \ refDivider
R = refFreq /channelSpacing

The IF is at 21.6MHz, I found it out by accident. While testing with a 10.7 in my formula, it received a strong signal  (Antenna is connected but mic is not connected, no dummy load yet). Using an Icom v8, I scanned the band looking for that signal. Then I work out the IF base on that frequency.

About TX/RX, is there a difference when setting the synth frequency for TX and RX? 

Thanks and Best Regards,

Noli - 4G1ZYS

Hello Noli
Very interesting. From the picture you provide I can see that the RX is a simple superhet, but not the frequency on the filter. 10.7 pr 21.4MHz is most probable.

The EPROM only contains programming data, as you stated, but you can use a DIP switch instead of the EPROM to program a single frequency. You can use two parallel DIP swirches with diode switching for TX/RX and if you get the numbers right you can use a BCD thumbwheel switch to get a range of channels. All instead of the EPROM.

All you need do is look at the spec of the synth chip and get the info into it.

They usually program the reference divider (R-counter) to give you 6.26kHz or 12.5kHz (L5, L6 & L7) so that can be hard wired for all combinations.
That means you can simply trnsfer 5x 4-bits of data, but in operation, get the numbers right and you need only transfer one byte for TX/RX.

I have an EPROM burner here when you have got the code sorted out.

Do NOT tune the inductors yet. You need to get a signal through the IF stage before you start adjusting anything.
Also, you can use a signal genertor to inject a signal. You should only need to tune the RF front end (with a plastic tool) when you get a signal through it.

BR Harry

Hi All,

Friend give me this radio as defective. I searched from google but found very little information. No spec sheet or user manual. It uses an old EPROM to store frequency information and I suspect that the EPROM is erased already because the top is already exposed. I went on to investigate on my own, luckily me, it uses an MC145146-2. With data from the datasheet, I am now able to program the PLL and already proven to be working.

I have an amateur license but this radio operates in 160MHz to ~171MHz, way out of the frequency I am allowed. How can I change the frequency range of this radio to the amateur band?

I am not very familiar with analog. You may wonder how I am able to program the PLL but clueless about changing the frequency range, it is because most of my work involves software. 

Below is a picture of the ?IF? section. Should I start turning those inductors?

Thanks and Best Regards,



Noli - 4G1ZYS