Trouble Getting to UHF Repeaters

Discussion in 'General Technical Questions and Answers' started by KE8QYV, Feb 22, 2021 at 10:47 PM.

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  1. KE8QYV

    KE8QYV Ham Member QRZ Page

    Hello, I am new to HAM Radio, just passed the Technical exam last week. I have BAOFENG UV-5R connected to a TRAM-1480 Dual Band antenna mounted outside. I ordered a TYT TH-9800 today, so that should get here on Friday. I have no problems connecting to the VHF Repeaters nearby with the UV-5R. I was trying to get on one for IRLP access that is about 18 miles away and although I was connected, I did an echo test and couldn't understand parts of my test message, so I decided to skip it. Either way, I was impressed I was able to connect and interact with the IRLP node with my little UV-5R. There is another VHF repeater about 13 miles away I can talk on and have a couple of pretty clear conversations. I found a UHF IRLP repeater about 13 miles away (same town as the VHF repeater I connect to), but I cannot connect to it for the life of me. I tried a few other close by UHF repeaters and nothing. Not even an acknowledgement from the repeaters. I am pretty sure I am setting them up right since I have no problems in the VHF band. I have never even heard anything from a UHF repeater when scanning, except on a couple I have heard some digital sounding noises.

    So... I am just curious if there is anything that stands out that I could be missing? It just seems odd I have no problems in the VHF band but nothing in the UHF band. I could wait until Friday when I get my new radio to see if it's related to the UV-5R, but I thought I would throw it out there and see what some more experienced folks have to say.

    Thanks!

    Ken Fitzpatrick
    KE8QYV
     
    KA0HCP likes this.
  2. N7WR

    N7WR Premium Subscriber QRZ Page

    Don't panic. Though 13 miles doesn't seem like much depending on how high or not so high above you the UHF repeater is , or what obstructions are in the way, the UV5R output is likely insufficient on UHF to make the trip. You generally need more power out on UHF than VHF all other things being equal. With your new, higher powered radio coming later this week you should be good on both VHF and UHF at that distance---also, don't know how much coax there is between the UV5R and antenna but there may be some losses reducing the already low power of the HT even more by the time it gets to the antenna
     
  3. KE8QYV

    KE8QYV Ham Member QRZ Page

    Thanks for the response, that's good to know about the power. I wasn't sure since the VHF channels sound so clear at 5w. I guess I don't know exactly how clear I sound though. Can't wait for my new radio. As for the coax, I am using 100ft of LMR-400 because I was worried about losses at 100ft.
     
  4. KD4UPL

    KD4UPL Ham Member QRZ Page

    Assuming a reasonable SWR on 70 cm your loosing roughly half your power in the coax; and assuming your Baofeng is putting out 5 watts (I doubt it) that means you're only transmitting about 2.5 watts or less.
    Even at that you may have something programed wrong. 70 cm repeaters typically use a 5 mhz offset, not 600 khz like 2 meter repeaters do. You likely need a PL tone but the repeater may require a DCS to get into it. Have you verified it's requirements in Repeater Book or some other way? Since you've never heard anything from the repeater are you sure it's actually on the air? Just because a repeater is listed doesn't mean it's operational.
     
  5. KE8QYV

    KE8QYV Ham Member QRZ Page

    I used CHIRP to program in about 80 repeaters within 80 miles of my GPS location. I used the Repeaterbook proximity query in CHIRP to get the info. During my scanning, I haven't heard anything from any of the 70cm repeaters except some occasional static or digital sounds (probably digital repeaters?). I've tried connecting and listening to about 4 of the closest ones and I have even tried to manually program them and then going back to CHIRP. I am leaning towards the issue being the output power of my radio. I have a TYT TH-7800 coming on Friday. That outputs 50w for UHF, so hopefully that will fix my issue.
     
    Last edited: Feb 23, 2021 at 3:31 AM
  6. W2SGM

    W2SGM Ham Member QRZ Page

    The loss is significant. Have a look at this datasheet for LMR-400 (specifically page two, the attenuation vs frequency chart):
    https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-400.pdf

    You can see that at 450 MHz it's pretty close to half, and that applies to receive as well. That figure is just the cable loss and doesn't account for any antenna inefficiency. Do you have any other options for antenna and radio placement? A 10x increase in power will definitely help, but you'll also have a 10x increase in loss.

    It seems that you've heard at least some UHF transmissions, so it's unlikely your radio's receiver is defective. If you want to be sure and can get your hands on an FRS radio, try transmitting from that and receiving it on the Baofeng. If it's exceptionally weak at a distance that seems reasonable (say, from across the house), there might be something wrong with the Baofeng's RX. Keep in mind that the Baofeng can't legally transmit on FRS frequencies.
     
  7. KE8QYV

    KE8QYV Ham Member QRZ Page

    Sounds good. I'll just wait until Friday for ny new radio.

    Speaking of loss and antennas, here are the parameters I am looking at:
    5 w Transmitter output
    Tram 1480 Dual Band Antenna - 8dB Gain at 70 cm, SWR less than 1.5:1
    LMR-400: 443 MHz at 100 ft = 2.666 dB loss
    Additional loss from SWR 1.5:1 = 2.792 dB total loss.

    When I plug that into the calculators at https://www.qsl.net/co8tw/Coax_Calculator.htm, I get an ERP of about 16w. Wouldn't that be the power of the signal leaving the antenna?
    I did the calculation for 2m (6 dB antenna gain at 2 m) and I get about 14w ERP. That makes it seem like I have more effective power at the 70 cm band.

    So, I don't know, I am still learning this stuff and its about experimentation. I am curious how the 50w transmitter will do. I was mostly wondering if there was something glaring I was doing wrong with the 70cm repeaters.
     
  8. K8XG

    K8XG Ham Member QRZ Page

    Your probably doing things fine. BF radios are known to be more deaf on UHF then VHF as well as lower output power. Programing 80 miles is pretty far for even VHF repeaters to hear on a $400 radio even, I'd cut that in half and then put that into the 7800 and I bet you will be fine if you actually have any operating in your area.

    Many places I have traveled to the Free Repeater listing was showing "Ghost Repeaters of a long gone day". The owner still owns the frequency pair, but the unit is not working or even probably not existing anymore. Most of the free listing just pull the files from the public records.
     
    Last edited: Feb 24, 2021 at 1:42 AM
  9. W1VT

    W1VT Ham Member QRZ Page

    Do you know what the 70 cm repeaters are used for?

    If they are used to link repeaters via RF links it is most likely that they are using beams at both ends of the path. This can make it very hard to get into the link.

    This is done because the Internet, while useful for linking repeaters, may go down in an emergency.

    Zak W1VT
     
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If there are open 70cm repeaters in the same general areas (sometimes on the same towers) as 2m repeaters and you're not getting into or hearing any of them, I'd refer to one of my favorite Chinese dishes:

    Sum Din Wong.

    I've used (and often owned) repeaters since 1974 and 70cm "range" is typically the same as 2m "range," since although there's more path loss, that's balanced by more antenna gain and they're really not much different.

    Around here, "most" 2m repeater sites also house 70cm repeaters, often using antennas on the same towers and repeaters in the same blockhouse "shack" and when I switch from one band to the other, pretty much nothing changes.

    I do suspect in your situation, Sum Din Wong.:p:)
     

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