WRQU355 Posted June 3, 2022 Report Posted June 3, 2022 Is there retuning required for use in 70cm? Anyone with experience in this? Quote
Lscott Posted June 3, 2022 Report Posted June 3, 2022 Which band split does your radio have? The brochure I have in my electronic library shows three, 400-430, 450-490 and 485-512. From my experience with various Kenwood HT’s they will function out to 3 to maybe 4 percent beyond the stated band split. For example the 450-490 split you might get it phase lock down to around 440 or a bit higher. The repeater section of the 70cm Ham band is 440-450, which I’m going to guess is what you’re interested in. There is more to it than just tweaking the VCO voltage to extend the lock range. The radios typically have band pass filters in the input section that are electronically tuned on the fly as the radio changes frequency. The radio’s micro generates the voltage fed to either a number of varactor diodes or inductors that vary their inductance based on a small bias current. I don’t recall seeing any adjustments in these type of circuits. Quote
WRQU355 Posted June 3, 2022 Author Report Posted June 3, 2022 Yes mine are the - 1 or 450-480 split. I found an article shortly after this question which stated they have retuned them and they are working fine. So I'm going to try that. Quote
Lscott Posted June 3, 2022 Report Posted June 3, 2022 59 minutes ago, WRQU355 said: Yes mine are the - 1 or 450-480 split. I found an article shortly after this question which stated they have retuned them and they are working fine. So I'm going to try that. Do you have a link for that? I would like to read it and see specifically what was done out of curiosity. I have some HT's that I specifically looked for, and purchased, with the 400-470 band split so no re-tuning was required. I was also gifted a NX-820HG mobile from a buddy, it was left over from a project that was canceled, nobody wanted it so he took it home otherwise it was going to get junked, which also had the 400-470 band split. The mobile shows up on eBay every once in a while. https://comms.kenwood.com/common/pdf/download/10_NX-720HG&820HGBrochure.pdf I had looked at some of the TK-480's for use on the 33cm band at one point. The info I read highly recommended swapping out the IF filters. The replacements where not an exact fit and required tweaking the pins to fit the PCB pads. I'm wonder if something along those lines might have to be done with the 880's. Quote
axorlov Posted June 4, 2022 Report Posted June 4, 2022 Mine "-1" works fine on repeater portion of the 70cm band. No retuning was needed. Quote
WRQU355 Posted June 8, 2022 Author Report Posted June 8, 2022 I'm not sure where the article went, but it was very simply retuning the vco voltages. If you grab a service manual and look at the alignment section. it will give three frequencies to check the vco voltage. Change the vco tuning frequencies and tune for specified voltages and all should be good. Much of the overseas market goes down to 440Mhz for commercial so the radio is designed to go there, but for US it is tuned upward. Now I'm trying to interface one with my TKR-840 to act as it's transmitter instead of the internal 5 watt one. axorlov 1 Quote
WRQU355 Posted June 9, 2022 Author Report Posted June 9, 2022 Well I abandon the 880 to repeater program as I found an affordable Motorola PA that will do the trick. Quote
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