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Keep talking guys. I am learning a lot.

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

If you look at the table, it's performance narrows and insertion loss increases as you approach 5MHz spacing. There is no way in hell that will have acceptable performance at 3MHz spacing.

Since it's in my repeater and my repeater has 5MHz spacing I would say that it can be tuned for that spacing.

Conflicting info 50W RF Power Handling 6 Cavity Design Minimum Tx and Rx frequency difference: UHF 3MHz Maximum Tx and Rx frequency difference: UHF 12MHz Fequency Range: UHF 400-470MHz(the full band) Bandwidth:±500kHz Standard Termination: N Connector Frequency Spacing: 8-10MHz Insertion Loss:≤1.0dB Nominal Impedance: 50Ω V.S.W.R:≤1.5 Suppression:>75 Isolation:>75dB Free Frequency Tuning Easy to build your repeater Weight:1.8Kg

Be careful, that specification indicates a minimum spacing of 8-10MHz between RX and TX, but the US standard for UHF is 5MHz.

That's the one.

Google is sending me to the same link as i found earlier ... Repeater Duplexer 50W UHF 6 Cavity Duplexer SGQ-450D -

If you broaden your search to “SQG duplexer” you’ll find several hits.

No reference to my-450-sqg-50 on the interwebby And the other number had no reference either.

That would be awesome to mess with for an afternoon. It's small, so it should be cheap to ship, too. If you want me to take a look at it, PM me and I'll send you my info.

I had an Uncle who was an Admiral in the Navy out of Groton. Passed away and only my Aunt is survived. No one in Rhode Island that I know of LOL

It's totally possible. The new one came nicely pack in a bubble bag surrounded by foam in a thin cardboard box. I just pulled it out and the old one that I'm storing in that box I checked the tuning screws and they are as tight as can be. And here's the original one that I replace with the one sent by Btech. Looks like a different brand, probably the cheapest they could find until they found out you need to buy them twice which isn't making it cheaper.

Glad I could help you spend money The black screen is definitely easier on the eyes in bright sunlight and at night. It's worth the extra $50 for me. I can't answer your question about swapping the remote heads between the radios since I have not tried it. I have not noticed any differences in the two radios except for the screen colors. Both work equally well on 2m and 70cm. I didn't bother doing the mod on my 2730B since I am not impressed with how my 2730A performs on GMRS. I've tested the 2730A against my TYT TH-7800 and my Wouxun KG-1000G. I've tried all three with my Comet CA-712EFC and Comet GP-9 antennas. The modded 2730 does not receive GMRS as well as the TH-7800 or KG-1000G no matter which antenna I use. And everyone says my transmissions are louder and clearer with the TH-7800 and KG-1000G

My son in-law just retired from the Navy (damn I'm old). He spent his last few years in Gronton, and lived in Preston. I still have family in Rhode Island and Florida too... funny coincidence. LOL

Ya, thanks for the offer. Up in CT so kinda far to travel. But maybe I'll get sick of working up and take a couple days off and go visiting. Got people as far down as Florida and Texas I'd like to meet up with some day to make the imaginary internet friend real friends.

It's been about a year since we got these and they are by far the most used radios in our household. We use them for simplex in the neighborhood when we're out walking or biking. They have had multiple slips, trips, and falls from bikes and scooters. We get coverage from inside the house to a point about 0.5 mi away in an urban neighborhood with lots of mature live oak trees. If both radios are outside, it's closer to 3/4 mi. I can hit a local repeater from inside Walmart at about the same distance without any problems. Actually, reaching the repeater can be done from inside my house at almost 2 mi away (elevation matters). For a <2W radio that's as small as the bubble pack radios and costs ~$13 ea, we've been very pleased. They're going back to the beach this year where it all started. There's more repeater coverage now so I'll have to reprogram them. I guess that's the biggest complaint is that there are not many DIY programmable channels. Otherwise, we've been happy with the purchase.

I'd love to get my hands on it to see if it's just out of tune. You may have 2 good duplexers now.

I think some companies will pre-tune them for you, but I would be concerned about filters with a more narrow filtering being shaken/vibrated out of adjustment during the shipping process. that may be why the first one you had didn't work so well. I may have asked this before, but if you are anywhere near DC, I'd be willing to meet up with you to tune one, or at least verify one you order stays in tune after you get it.

Yes, thank you.

Damn it, I was content with the 2730A and able to tell myself I didn’t need the 2730B and then you post pictures. I can’t resist pictures! You’re costing me money. In all seriousness though thanks for the comparison. I really like my 2730A. It does pretty good paired with a Comet SBB-5 NMO. I have been thinking about getting the 2730B and moving my 2730A to the house. Looks like it would be an improvement from the bright screen of the 2730A at night especially. Have you noticed any other differences between the two or is it just the screen? I was wondering if you can swap heads between the two? Reason for this would be to keep one with mod in vehicle with the black screen and have a non mod one in the home.

This ^^^

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.

The logical assumption is that there’s are CTCSS tones or DTCSS codes somewhere that you don’t realize are there, either on the FRS radio or on your other friends radios, or the radio is transmitting on frequencies the other radios are not receiving. We can’t really know for sure without more information, such as you posting a screenshot, a chirp file, maybe a device like the SW102 showing the output power and actual frequencies of the transmissions that others are not receiving. But we can speculate a bunch: Bad programming. Bad firmware. Both. But here’s something to try. When it’s transmitting and other people’s radios don’t seem to receive it, put your UV5R into “scan for tones” mode to see if it’s actually sending with a tone that the other radios filter out.