How to AVOID Blowing Your Repeater Up!

One of the 2M repeaters in our system all of a sudden dropped in signal strength one day... so I took the opportunity on a nice day to head up to investigate what the problem might be.
More ham radio repeater adventures 👉 • Ham Radio Repeaters
⏱️Chapters⏱️
0:00 Problems
2:30 The role of an isolator/circulator
6:07 Troubleshooting steps
7:56 There's ya problem!
8:54 A fix, of sorts
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[@K2DXK]

You know your stuff 👍👍 I’d love to see more repeater maintenance videos. You’re one of the few KZbinrs if not the only one who knows real RF.

[@HamRadioDX]

Thanks! I'll make sure I do more!

[@dfestus]

Thanks for taking us along for the ride. I maintained several repeaters here in the US for decades. I have seen the inside of a cellwave super station master fiberglass radome antennas turned to dust in a microsecond by a lightning blast. I totally appreciate what you do. 73....

[@HamRadioDX]

Thanks! We're lucky that lightning is *that* big of a problem - I mean we have a 200 foot lightning rod in the form of the broadcast tower right next to us. Plus we don't get that many storms in our part of the world, so we're kind of lucky.

[@mikesradiorepair]

Must be nice to have blacktop roads to get to the repeater site. Most of the sites I service are dirt mountain roads or should I say goat path. Washouts a foot or more deep, 18 inch deep standing water in places and I swear every tree branch on the mountain trying to wipe all the antennas off my roof.

[@billfargo9616]

You'd expect people paying property tax to support paved roads past their homes to not live on the road to the repeater?

[@HamRadioDX]

Every advantage has it's disadvantage... I'd rather an offroad 4WD track... less traffic to deal with (idiots) who don't know how to use the road! All our other sites are 4WD tracks with varying levels of accessibility.

[@Ken-W1KAL]

Great explainer on circulators! Maybe someday I will be able to ping this repeater…

[@seanwieland9763]

2:42 🎶 It’s time for the circulator. It’s time for the circulator. Circulator. 🎶

[@ki4rex]

Great video. Thanks for the info. Building my first repeater system now

[@VK4GEO-DarrinArcher]

Thanks Hayden. Really like this sort of content mate. Well done.

[@Videostufftas]

Excellent video thanks Haden 😊

[@g0fvt]

Circulators are great devices, pedantically the Isolator is a Circulator fitted with a load. They work using an effect with a precessing magnetic field. FWIW I used to maintain base stations for emergency services here in the UK, one type in particular had a thermal switch on the dummy load that was used to trip the transmitter to low power in the event of a prolonged period of transmit into a bad SWR. Not a bad solution, to ensure that the radio continued operation even with a faulty antenna. Maybe you could have something similar on yours? A thermal switch to trigger a warning on the ID beacon?

[@HamRadioDX]

That's a great idea! Yes you're right regards the difference between a circulator and isolator

[@g0fvt]

@@HamRadioDX well done on your explanation by the way, some comms sites over here demand isolators due to IMD issues.

[@alzeNL]

What a fascinating video, having never seen the insides of a repeater, this was a brilliant introduction. I really like seeing the hardware that makes the repeater function and the HP analyzer is a great bit of kit ! Thanks again. 73 2E0FWE

[@HamRadioDX]

Thanks for the comment! I'll have to do some more videos showing the workings of the repeater systems around here!

[@VK7DBX]

I'm glad she's fixed 'cause I'll need it soon. But on a serious note, i think Tassie is lucky with some good locations and a great team to maintain our repeater system.

[@HamRadioDX]

I gather you passed on the weekend?

[@VK7DBX]

Yes, just waiting on our friends at the ACMA

[@MikeinVirginia1]

I never understood what a circulator actually did until you told me!

[@DesertRatLife]

I know your pain. always something to fix.

[@autonomous_collective]

Ground the coax-cable(s) on the repeater(s).

[@HamRadioDX]

They are grounded

[@Subgunman]

On the isolator, I use isolators that have an external load. This way if I have high power transmitters next to my repeater, the isolator will shunt the RF into the load. I use loads that can handle about 200 watts to handle not only my repeater but all of the RF trash that might enter through my antenna. Another way to eliminate intermodulation issues is to do an intermodulation study on the site. This requires knowing all of the transmit frequencies as well as the power output of each transmitter.

[@HamRadioDX]

I'd prefer a circulator so I could have a larger load... but they are expensive devices. I was lucky to find this one and get it tuned onto 2m - but I think the load rating is over the top... it gets warm with 100W through it with a complete open circuit on the output. web.archive.org/web/20170710142600/www.rfiwireless.com.au/multicoupling-monitoring/system-components/ferrite-circulators-isolators/isolators-circulators-single-isolators-sp1317-3115-11.html#tab_spec

[@Dieseleux]

Folded dipole are one best antenna for repeater, is ground, is wide bandwith, is highly reliable. one or two bay for large lobe local communication, 4 bayfor better distance coverange, 8 bay in uhf for low altitude high distance signal. On high altitude like on this video , 2bay vhf or 2 to 4bay uhf are very nice

[@HamRadioDX]

Yes, we're ordering a couple of Low PIM folded dipoles!

[@AECRADIO1]

IF UHF, GET A DB-420. BEST dipole antenna around!

[@HamRadioDX]

@@AECRADIO1 nah got VHF

[@tonybaldwin007]

Great video, can you drop a link for the isolator/circulator, like to get some more information on it. Cheers Mate!

[@HamRadioDX]

web.archive.org/web/20170710142600/www.rfiwireless.com.au/multicoupling-monitoring/system-components/ferrite-circulators-isolators/isolators-circulators-single-isolators-sp1317-3115-11.html#tab_spec That's the link to the old specs... it's not a current model anymore

[@Trent28888]

all the RF up on the mountain is burnin out the antenna,i wonder what the voltage is inside it

[@Franky6767]

Cool video, any link for the circulator?

[@HamRadioDX]

It's an old isolator... I had to find it via archive on wayback machine. web.archive.org/web/20170710142600/www.rfiwireless.com.au/multicoupling-monitoring/system-components/ferrite-circulators-isolators/isolators-circulators-single-isolators-sp1317-3115-11.html#tab_spec

[@GuitarNewby]

Put up a folded dipole array and be done with antenna problems 👍.

[@HamRadioDX]

Folded dipole arrays can still have issues with phasing harnesses getting water in them.. Best to run equal feedlines down into the building and put the harness there. But, the other issue is we are height restricted with our antenna.

[@IrishHamRadio]

Excellent description on the isolator/circulator….. As a keeper myself I might look into one of these.. However I am a little confused on the operation of your one….. If your antenna was busted, should not all of your rf output go to the dummy load? And if it goes to the dummy load, how would you hear that any distance from the site… Is the isolator also not doing its job correctly or am I misunderstanding?

[@HamRadioDX]

The output power out of the duplexer is 60W or 48dBm, coax loss is negligible. I tested the signal as being 30dB down, which would mean 18dBm or 60mW. A 100:1 SWR is only 14dB mismatch loss, so I suspect there is a high impedance break somewhere on the antenna matching section (and there is still some leakage of RF output power out - i.e. the 60mW) being radiated. The rest of the power is being dumped into the load. The obvious giveaway was the repeater going from an S9+20dB to about an S3/4. The job of the isolator is to stop any reflected power going back into the transmitter's PA and blowing up the final output device, so in this case it went into the dummy load with a very small amount being radiated.

[@IrishHamRadio]

@@HamRadioDX Ah yes.... You must be quite close to the repeater site so to still have been able to receive it at that level of what I suppose you could call ERP. At least the room got a little free heat from the dummy load! Cheers for the clarification Hayden 😊

[@HamRadioDX]

@@IrishHamRadio Yeah not too far - LOS in fact!

[@robertmeyer4744]

lucky you have back up antenna . circulators are a great thing on transmitter. fancy repeaters with remote mentoring can add temp of dummy load to the data . The GMRS UHF repeater I re done last year still going strong. has better range with M & P coax. that is not long. all on floor of a office budling. their is a cell tower and DTV station on main tower outher side of building. only a 2 meter ham and 800 /900 MHz repeater on side with GMRS . have to take apart antenna to find out what happened. inspect feed line as well . and any lightning protector like a poly phaser ETC. had them go bad, good ones have a replaceable arc tube. I keep spares in repeater cabinet which is locked up. sounds like antenna it self. does RX . 73's

[@HamRadioDX]

Yeah we installed a backup antenna specifically as this site is pretty harsh weather wise.

[@bentheguru4986]

Now, not knowingt eh setup and radio hut, I am going ask, have you got lightning arrestors on those LDF feed lines and why are they just handing around rather than secured/bonded?

[@HamRadioDX]

Yes and they are secured/bonded to the cable tray above at 10:04

[@bentheguru4986]

@@HamRadioDX Sorry, didn't see it.

[@stormshadow_6477]

So circulators for VHF do exist! Only ever found microwave ones when looking them up online^^

[@HamRadioDX]

They are really expensive! Luckily these ones were tunable and pulled out of commercial service just above 2m.

[@AA0Z]

Repeater gremlins....it's a full time job sometimes!!!1

[@aussiedazvk4djh889]

🤞

[@kesfitarkanozguc2792]

Dear Sir, I would like to ask question, I bought ACOM 1500 , Do I have to use all power or Can I set it low powers like 800 or whatever ?

[@alzeNL]

you need.a 1KW burner and coax made from steel.

[@DD5LP]

Yes you can run an amplifier at less than it's maximum output power. Some models have a control to do this. If not simply turn down the drive power from the transceiver.

[@kesfitarkanozguc2792]

@@DD5LP Thanks answering my qestion.Now .I am going to ask anotherone ACOM 1500 1200watt continuous power If I set my FT710 40watt or something Do I get less than 1200 watt ?

[@kesfitarkanozguc2792]

@@DD5LP because ACOM 1500 says (1200 W continuous carrier) output power with less than 85 W exciter drive.

[@DD5LP]

@@kesfitarkanozguc2792 I would expect so. However it's best to ask ACOM (or their dealer) as there may be a point where the amp misbehaves or automatically turns off with lower that expected drive. If the amp were the old class A amplifier I don't think you would have an issue but many modern amps run in AB classes rather than A. I would not expect any damage to the amplifier with lowering the drive, rather the additional logic In the amp may shut the amplifier off. Given that ACOM sell their Amos into countries where the maximum allowed output is 400W they will have a solution for this reduced output power need. It should really be documented in the user manual. Ed

[@mrtechie6810]

I recommend not planting expl-sives at the repeater site. Might help. 😂

[@alzeNL]

its australia, its a requirement.

[@mrtechie6810]

​@@alzeNLpoisonous snakes and spiders, maybe

[@Bikemen61]

You should have just used the duplexer and hooked up both TX and RX to the good antenna. What you actually did was not the right thing to do.

[@HamRadioDX]

Nope, I did the right thing. We have intermod being generated nearby in the near field of the antenna (probably something rusty) so we get desense when we transmit on one antenna. It doesn’t desense into a load. Splitting the antennas helps with that. It’s all experimental.

[@billfargo9616]

A circulator allows a single antenna to simultaneously transmit and receive.

[@VTXHobbies]

Any antenna can do that, it's the proximity to the transmit frequency that causes problems. That's the job of a duplexer. You're a tad bit misinformed I'm afraid.

[@BVN-TEXAS]

A circulator should be a mandate on a repeater. If you can afford a repeater, you can afford a circulator.

[@glenmartin2437]

Thank you. N0QFT

[@HamRadioDX]

You're welcome!