Baofeng’s desense when using external antenna is not true for everyone.

Cignus UV85

Modulation with DV1XKG and DV1YWJ both North Caloocan station to Las Piñas on Cignus UV85 a Baofeng UV5R variant for Philippine market. The portable radios internal squelch level was adjusted using Chirp. The modulation fix was applied using hardware modification by disabling the VOX function and use it as preamp for microphone instead.




The complimentary video by DV1XKG from his side, I’m still using the Baofeng with modify squelch level and hardware modulation fix. Notice that even on 1 watt my transmission can still be copied on his side with a quality audio which is not possible with Baofeng default microphone without hardware modification.




What can you say about this, share your comment below…

Some hardware modifications for Baofeng’s UV5R/UV82

Baofeng's

Here are some hardware modification to improve your Baofeng’s radio performance. These are not my own but an article found on the internet from DG2IAQ and KX3DX. If you’re into fixing and breaking things then this article is a must try. I have done some modification on my radio and I can say that the performance enhancement is worth the trouble. See the preamp modification using Vox transistor here.




Modification-Sheet-Baofeng-UV-82L-UV-5R

Another modification lists from KX3DX for UV5R.

UV-5R_tech_discussion_fixes

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Taming your stray RF that causes intermittent SWR reading by using RF Choke

rf-choke

Antenna system works depends on a lot of variables. Radio signals are affected by antenna efficiency, feed line loss, nearby objects, terrain, weather and a lot more factors that are beyond our control. It is difficult to control all factors but we can limit ourselves to optimizing those things that we can control. Like limiting stray RF from travelling to our feed line and cause an intermittent SWR reading.




SWR or Standing Wave Ratio is a measurement of antenna efficiency. When you are transmitting you are sending Radio Frequency along your antenna feed line. The antenna then converts this RF energy to Electro Magnetic energy which is radiated into space. If the antenna and feed line are not working efficiently some of this energy is reflected back to your transmitter along the feed line, thus it becomes wasted energy.

SWR is the ratio between transmitted or Forward energy to the Reflected energy. This ratio can be computed as:

SWR = Forward + Reflected/ Forward – Reflected





The most common piece of test equipment used to tune and test antenna system is an SWR meter. This tool can give you a lot of information about antenna, and can help you to tune your antenna’s resonant frequency, adjust antenna impedance.

So normally when we tune our antenna without using those expensive antenna analyzer (they are handy when doing frequency sweep analysis) we just use our trust worthy SWR meter coupled with our hand held radio and insert the SWR between the radio and our antenna system. In tuning the antenna we select the center operating frequency that we desire for our antenna to have a lowest SWR reading (resonance). We normally set the radio to the lowest transmit power to tune the antenna and to limit the interference we might cause while tuning. Once the acceptable reading is achieved we can expect that the tuned antenna will perform the same or with very minimal deviation on the SWR reading even if we increase the power applied to feed line and the antenna.

Sometimes this is not the case and we can expect a linear increase in SWR measurement with respect to increase of power applied to the antenna system. The way choke work is simple, a small amount of RF radiates from the shield wire in the coax. RF emitting from the antenna surrounds the antenna with a very large pattern filled with RF. Some of it gets on to the coax and can travel down the entire length of the coax, additionally a slight mismatch will cause some RF to be reflected comes back down the surface of the coax.

The RF choke creates an electromagnetic field on the chokes surface, and within the donut hole. This field attracts the stray RF and chokes it off before it travels down the coax, and it is dissipated within the electromagnetic field. Hence the term “Choke”. In some ways, it almost acts like a ground radial and reflects slightly the RF radiated from the antenna, to a more upwards angle sending more of the signal towards the horizon. But unlike a ground radial, the choke does not tune the antenna to any specific frequency. So it is good for all frequencies from 160 through 6 meters.

Here’s a video link demonstrating effects of RF choke on SWR reading, using the home brew choke I made. Pardon the audio it’s not meant for broadcast




Feel free to comment, constructive criticisms are very much welcome:
(Please read the provision for the use of Emergency Channel assignment in the 2m Philippine amateur band)

The center frequency of Philippine Amateur Band (Amateur Radio Service) for 2m happens to be 145Mhz the frequency assignments is from 144 – 146Mhz primary.

The center frequency is currently assigned to
Emergency Channel the channel assignments mentions the following provisions:

3.1 Channel 145.000 Mhz +/ 25KHz shall be used for emergency communication and general calling for radio telephony.

3.2 To facilitate the reception of distress calls, all transmission on 145.000 Mhz shall be kept to a minimum and shall not exceed one minute.

3.3 Before transmitting on the frequency 145.000 Mhz, a station should listen on this frequency for a reasonable period to make sure that no distress traffic is being sent. This provision does not apply to a station in distress.

The above video are for educational purposes only and there was no intention of breaking the above provisions on my part. However since these videos are made using the center frequency as reference it is good to note that the same frequency assignments can be used for general calling for radio telephony. (General; in my interpretations means the same frequency can be used provided that there is no distress traffic going on the channel (subject to other interpretation), and the transmissions shall not exceed one minute (must be 1 minute continuous transmission without gap), and care has been taken to listen carefully on the frequency to be sure that there is no distress traffic being sent.

3.4 Distress communications

3.4.1 The distress call sent by radio telephony consists of:

-The distress signal MAYDAY spoken three (3) times
-The words THIS IS (or DE spoken as DELTA ECHO in case of language difficulties).

3.4.2 The radio telephone distress message consists of:

• The distress signal MAYDAY.
• The name, or other identification of the mobile station in distress.
• Particulars of its position.
• The nature of the distress and the kind of assistance desired.
• Any other information, which might facilitate the rescue.

3.5 Any station in the amateur mobile service which has knowledge of a distress traffic and which cannot itself assist the station in distress is forbidden to transmit on the frequency in which the distress traffic is taking place, until such station receives the message indicating that normal working may be resumed.

Low modulation fix Baofeng UV-5R using built in VOX preamp transistor

If your baofeng UV-5R radio suffers from low transmit audio or low modulation this modification will help in improving your modulation problem. This fix will use your radio VOX preamp transistor to amplify the audio from the radio electret condenser microphone. Using this modification will disable your VOX function so don´t do this modification if you want to use your radio VOX function. As I have no use for it and I am not satisfied with the VOX sensitivity, I preferred this modification which was originally done by PA3FYM. This modification is different from I recently published modification by DG2IAQ which simply replaces and remove some of the capacitors on the UV-5R board.




The modification by DG2IAQ can be found here: https://drive.google.com/file/d/0B0…





If you want to retain your VOX functionality follow the modification by DG2IAQ. Since I have no use for the VOX function and the surface mount devices are difficult to source here locally, and the available components I have are too big to fit under the UV-5R LCD I will do the modification by PA3FYM which just require a single resistor with a value of 500-1000 ohms to couple the transistor emitter to ground. I use a donor board of an old VGA computer card to source the resistor and I found a 900ohms surface mount resistor which is just perfect for this modification. It is important to have the right tools for the job as it is difficult to work with surface mount devices and the UV-5R board is easy enough to damage with an over heated soldering iron, but of course you can do it with soldering iron alone with a little difficulty. I have a rework station and a little experience in handling surface mount devices, but still it is not a walk in the park.


Donor board a VGA card, twizzer, sharp blade, soldering paste, flux. screw drivers and rework station

The modification of PA3FYM. (Do this at your own risk). The schematic of UV-5R radio can be downloaded from the link here on my Google Drive.

PA3FYM
PA3FYM low modulation fix using UV-5R VOX preamp

The transistor involve in this modification is a 2SC1623 general purpose audio frequency amplifier on SOT-23 package mark as L6 on the UV-5R board. We need to lift the emitter and connect a 500-1000ohms resistor to ground. I found a 900 ohms resistor from the VGA donor board and itś just perfect for my use.

The data sheet of the transistor can be found from this link for reference:

A knowledge in reading the schematic is useful when cutting the tracks on the PCB between the inductor L44 and capacitor C137. The track is in the middle of those two components.

voxmod

This is my modification magnified< This is the modified board with the above modification. Baofeng UV5R Modification

Modification on my UV-5R radio

Make sure to test your modification before assembly to make sure your radio will still work. So I did…

perfect

So luckily the operation is perfect and radio is still able to power on 🙂

I have tested the changes and the radio is now sensitive in picking up my audio even if the radio is more than 6 inches from my mouth.

The original thread of the modification can be found from this site:

Good luck on your radio modification. Cheers! de DW1ZWS.