Warning: Since this article got so many views, I have to inform you that modifying your radio to transmit with higher power or out of the CB-band is illegal if you are not a ham. In addition: Warranty void

Info: This article is regularly updated with new information.

Lately I got the chance to work on a new PNI Escort HP 7120 to improve the FM modulation. Moreover, I found some special options that turn the radio into an 10m Ham Radio transceiver. Read along to find out about the advantages and disadvantages of this new and cheap radio!

Inspection

In this picture you can see the inside of the radio. On the top right part of the PCB you can find three potentiometers. They are labeled “AM MOD”, “4W” and “1W”. “AM MOD” sets the AM modulation. For AM the factory setting was already OK (overmodulation already occurred when speaking to loud into the microphone). The “4W” potentiometer sets the transmitting power. The maximum is about 5.2 Watts. The FM frequency deviation was increased by turning the potentiometer on the left side. For checking the bandwidth in FM, a SDR was used. You can set the channel width in your SDR software to 10kHz to check if your FM deviation is too big (compare the displayed box in SDR# with your signal in the waterfall diagram). The bandwidth of your signal should never excess 10kHz otherwise it will interfere with the neighbor channel. Unfortunately, the PNI has a problem with FM. The frequency deviation is stronger in the “positive direction” than in the “negative direction”. Strictly speaking this creates interference with the higher neighbor channel before the signal even touches the area of the lower channel and therefore reduces the maximum usable FM deviation. I will take a deeper look into the circuit of this radio to fix this problem as soon I have my own one.

You can see the asymmetrical FM spectrum in the waterfall diagram where I said “KKKKK” in the end of the transmission.

Here you can see that there is no thermal compound between the case and the driver transistor for the final TX stage. It might not be necessary but I added some.

Options

The PNI has two jumpers that allow you to change the radio to a 10m Ham Radio or to a dual mode device (Ham and CB). In addition, different CB standards are available without changing the jumpers. For changing the standard (or band), first switch of the radio. Press and hold the “A/F” button, then turn on the radio. Now you can release the “A/F” button and change the standard with the arrow keys. To save the standard simply turn your radio ON and OFF again.

By holding PTT and RFG together and then turning the radio on, you can switch to high power mode which increases the TX power to 8W. This only works when at least one jumper is on.

Standard modes

Should be described in the manual.

Jumper setting:

OP1: OFF
OP2: OFF

Jumper setting for CB mode but with 8W TX power:

OP1: ON
OP2: ON

CB + Ham Radio Mode

The band "DE" is equal to the CB-channels 1-40. FM and AM is available on all bands. Power is 4 Watts and drops about 1 Watt near 30MHz. Channel step is 10kHz (as on CB). Between the channels 3 & 4, 7 & 8, 11 & 12, 15 & 16, 19 & 20 the frequency step is 20kHz on all bands. High power mode can be activated.

Jumper setting:

OP1: ON
OP2: OFF

FM and AM is only recommended in a small part of the 10M band. Revere to your local band plan to learn what channels you can use. I marked all possible channels in yellow (there could be repeaters or digi modes) and all recommended ones in green (10NFM channels) following the Austrian band plan in the Excel-sheet you can download below.

Ham Mode

In this mode the channel step size is constantly 5kHz. FM and AM is available with 4 Watts of power. High power mode can be activated.

Jumper setting:

OP1: OFF
OP2: ON

I found it very interesting that the band labels are starting with "H" and go from 28MHz to 29,695MHz (exactly the Ham Band). Of course the same band plan rules mentioned before also apply here.

Downloads

This Excel-sheet contains the frequency for every possible channel on every band.

All frequencies for CB+HAM Mode as PDF
All frequencies for HAM Mode as PDF

First test on 10 meters

On Saturday the 21st of November I tested the PNI on channel 30, band “HE” (29105kHz) in CB + Ham mode. High power mode (8W) was also activated. Unfortunately, I had no car antenna tuned to 10m, so I used my CB antenna. I think the SWR was >2 so I expected no big success. Nevertheless, I reached OE3AMQ who was about 12,7km away. My QTH was the 300m high Pankraz and I received OE3AMQ with S3 R5 on the PNI (he transmitted with 5 Watts). He gave me S3 R3-4 witch was OK for the unmatched antenna. In conclusion the PNI seems to be useful on 10m and is a great radio for mobile use. Sadly, 10m is very silent in my area. Maybe this will change with this cheap radio. Further tests will follow!

Hardware improvements

I started to do some audio measurements on the microphone and modulator circuit. The results will be used to optimize the sound of this radio. Furthermore, I documented the reverse engineered circuit parts for future hacks.

Integrated Circuits & Transistors

List of the main ICs and transistors of the PNI radio. Datasheets available online unless otherwise noted.

Audio measurements on the original radio

I did some basic audio measurements with an Audio Precision to check the quality of the transmitter AF path because many users in online forums and on air stated that the PNI sounds dull. Everything measured with the amplitude modulator transistor desoldered + radio in TX mode.

This diagramm showes the original frequency response measured between the microphone input and the FM modulation potentiometer. The low pass characteristic seems OK but the high pass characteristic ( Pre-Emphasis ) is to flat. A magnitude change of 6dB/octave (through the whole passband) is standard for narrowband FM transmitters. Pre-Emphasis in FM means that high audio frequencies are transmitted louder than low frequencies. This is necessary due to high audio frequencies "faster" disappearing in the noise when using frequency modulation. To normalize the audio again in the receiver, De-Emphasis is performed. Strictly speaking, if the Pre-Emphasis is missing in the transmitter the high audio frequencies are transmitted to quiet but the volume of high frequencies is still reduced in the receiver (De-Emphasis applied) and you get a dull sounding signal.

In the point of view of an audio technician the THT + Noise (Klirrfaktor + Rauschen) was quite bad over the whole AF range (300Hz to 3400Hz).

Even worse on lower audio levels.

In this picture you can see that the gain was negative (attenuation). This seems very strange but I checked my measurement setup several times and found no error. Maybe it was caused by the onboard audio compressor.

The PNI has some discrete circuitry in its AF path that look like an audio compressor. Tests showed that this feature reduces overall gain and causes a bad THT. It should be disconnected. A compressor isn't really helpful in FM. I will describe this and other improvements in the next paragraph.

Improvements

Documentation seems to be lost by now, but it looks like nobody is interested any more anyways.

Measurements on the moded radio

Comming soon.

The frequency modulated spectrum is now symetrical around the carrier frequency, even if I say "KKK".

Audio examples

Original Test Audio that was played through the PNI radio.
Rcorded Test Audio from SDR#.

In my opinion the radio sounds very clear now. Maybe the high pass characteristic is a little bit to strong but on air all station said the modulation is OK.

Other radios

The described modifications might also work on the following radios:

If you have one of these radios and confirmed that some modifications work, please write an E-Mail to the address listed under "About".