Lscott

Everyone should review this old thread.

The attached file is an example I did to do a hex edit hack on a Kenwood NX-411 code plug to get on the Ham 33cm band. The radio programming software wouldn't allow the entry of the frequencies. How to Hex edit Kenwood code plugs - 20241011.pdf

You need to get a windows hex editor. Then you can load in the binary file and edit the specific memory location. https://en.wikipedia.org/wiki/Hex_editor https://www.av-rd.com/knowhow/data/hexedit_archivists-1.html

See attached file and read the instructions below I had found on-line some time back. ==================================================================================== KPG49D v4.02 Password Bypass -> KPG49D.exe: 0x0000418A change 74 to EB Once modified, when the Data Password dialog box opens, just hit enter or type anything and it will then go onto read the codeplug. The password is located in the .dat file at 0xB5-0xBA. KPG-49D V4.02.zip

If it satisfies your communication requirements then it was a good choice.

Without knowing what frequencies are being used locally there I think that would be a dumb idea. There are warnings all the time against taking FRS, same frequencies as GMRS, radios on foreign vacations since the frequencies could be used by local fire, police etc. services.

I've held off spending money on one of the tiny VNA's since I'm not really convinced they have the dynamic range claimed. I would like to see some verification of the spec's testing against a know high quality lab bench VNA. For tuning these cavity filters you really need the high dynamic range to be sure you have all of the cavities aliened.

I've looked at the spec's for the man-pack radio itself. https://en.wikipedia.org/wiki/AN/PRC-77_Portable_Transceiver At 1.5 to 2 watts for the size at the time seems crazy now days. Just think what a modem commercial, not military, grade P25 HT can do , 5 watts and with AES256 encryption. It would fit in a uniform shirt pocket. I also checked the spec's on the old WWII handie-talkies. I was shocked to see they only did 360 milliwatts! Remember that while watching those old B/W WWII movies. https://en.wikipedia.org/wiki/SCR-536

It might be a secret credit card number to use, billed direct to the government, when ordering out a pizza for deliver.

That's correct.

As pointed out FRS channels 8-14 are low power, 0.5 watts max. That's why mobile radios don't include them since they generally can't lower their power to the legal limit, otherwise GMRS and FRS radios use the same "simplex" frequencies. FRS does not have access to the repeater input frequencies whereas GMRS does. Second if you have a GMRS license it's perfectly legal to communicate with FRS radios, even above 2 watts. On channels 1-7 you can use 5 watts max, and on channels 15-22 it's 50 watts max. The point to remember is FRS radios use exclusively narrow-band FM while GMRS uses normal, wide-band, FM. If it's possible using a GMRS radio the bandwidth should be set to narrow-band when talking to FRS radio users. I use mainly commercial grade radios for GMRS. Those have the ability to use either bandwidth. For those radios I program in two banks of frequencies, one wide-band for GMRS, and the other narrow-band for FRS. FRS-GMRS combined channel chart.pdf

The simple explanation is one is used to isolate the transmitter from the receiver. Since the repeater is a full duplex operation, transmit and receives at the same time, any RF energy from the transmitter will get into the receiver. When this happens the receiver will trigger the transmitter. Now you have a feedback loop where the system will stay locked up on transmit until the power is yanked, destruction of the receiver's input at worse, or simply kills the sensitivity of the receiver then it becomes deaf to weak signals. The typical notch/bandpass duplexer filter is setup such that the receive half of the filter is tuned to notch out the transmitter's frequency as much as possible. The bandpass filter on the transmitter side is tuned to eliminate as much of a spurious signals that are not on the exact transmitter's frequency, thus preventing them from entering the receiver's circuits. For the above to work a certain frequency minimum difference between the transmit and receive frequencies are required. This minimum depends on the quality (design) of the duplexer. https://horwin.info/en/pro-dupleksery/ https://www.repeater-builder.com/antenna/pdf/w6nbc-duplexer-book.pdf

It was also known the NV had captured US man pack radios. These where used to monitor military communications. There were versions with encryption, but were extremely bulky. https://en.wikipedia.org/wiki/NESTOR_(encryption)

At least on the official side. My buddy has his "export" mobile radio for 12/11/10 meters. He's run FM on 11M with a few people, and that's before the FCC allowed it. The question will it replace FRS. I think the answer is no. Why. The usage cases are different. People using FRS have short range communications requirements. The small size, radio plus antenna, fit in a shirt pocket or on a belt very easily. Anyone that's looked at some of the older "HT" style CB radio, well they're about the size of the old WWII walkies-talkies. The antennas for any reasonable radiation efficiency are ridiculously huge. These radios are not convenient to use. The retired cop in my radio coffee group tells us stories how the older Motorola radios were not liked that well. They were large, bulky and the officers complained about the antennas poking them in the armpits all the time with the radio on their utility belt.

I've had the same experience with the monster sized dual band Ham antenna on my ride. https://forums.mygmrs.com/gallery/image/471-mobile-mount-with-antenna-rear-view/?context=new It doesn't look like any common "CB antenna", but I guess people just go with what the are familiar with.