Successful Handy Based Repeater? (ie. Baofeng/Retevis)

[WRUH396]

Quick Question

Not looking for tech advice necessarily, just experience if anyone has seen or done this.

Has anyone made or seen a successful deployment of a Duplex Repeater (not simplex store and repeat) built with inexpensive Handytalkies?  

I have seen quite a few Youtube videos of people attempting to do this with UV5Rs but I have have never seen one that I would consider successful. 

My thought is, that if you used two separated antennas instead of messing with a power eating Duplexer this should work.  Most the videos I have seen, it looked like the close proximity created so much de-sensing that the range was total garbage.  HOWEVER, in my mind with the proper shielding, maybe some RF-Chokes on the Audio Cross Connect and this absolutely should work... Right?  I may try it on my own to see what I can do but I figure somebody else must be familiar and have experience with such a set up.  While I have a fairly strong repeater at home, I also have access to a location 1000 feet over the valley floor and I am considering running a small test repeater to see if it would be worth moving my main repeater over there.  I won't preemptively move my main repeater because I do not have line of site to that location and I can bet cheap Handytalkies will not make it from home like it does on my repeater in the garage but it would be nice as a secondary repeater when I am out mobile.  

[WRKC935]

OK, you are NOT going to get enough physical separation of the antenna's to get it to work correctly.  So that's the FIRST problem.

Second issue is you are using radios that due to their size have little to no filtering.

If the thing was to talk more than 100 yards, you would be doing good.

And your 'power robbing' duplexers are the ONLY way it could possibly work. 

Let me run this down in real numbers in a manner that will make sense.  And the ONLY way you could POSSIBLY get it to work.

If you can get the antenna's 20 feet apart on a vertical plane.  Meaning one antenna 20 feet directly above the other then you will get about 15 to 20 dB of isolation.  For every 20 feet increase you can add 10 dB to that.  You need 80 to 90 dB of isolation for a repeater to work correctly.  So if you can place the top antenna 200 or so feet above the other one, then you have enough isolation.  Of course the bottom antenna that you are transmitting on is at ground level, and the receive antenna is 200 feet in the air so it will hear ok, but not be able to talk very far.  Second issues is unless you dump a bunch of money into 7/8 hard line (with 1.5 dB of loss per 100 foot length) the loss on the receive side is going to be higher than the loss of a 'power robbing' duplexer. 

But it's STILL a portable with poor shielding, so the transmit RF is still gonna get in the radio and screw with the repeater function and desense the receiver in that hand held. 

You could of course run a 200 foot linking cable down the side of the 200 foot tower linking the radios together, but that will pick up a ton of static and electrical noise and cause other problems.

Bottom line is this, you have never seen this work because it don't.  ANd no amount of screwing with it is gonna get it to work. 

If you have a spot that has 1000 feet of elevation over the area you are wanting to cover and you have a repeater, move the thing.  Install a LOW GAIN antenna, I would say 3dBi MAX. Reason is that an antena with gain is NOT an amplifier.  If can't increase the signal level through amplification so it does it by concentrating the radiation pattern.  A unity gain antenna has a pattern that looks basically like a donut from the side.  A gain antenna flattens that donut on a vertical plane.  So the pattern goes up and down in equal amounts.  If you get too much UP then the area under the antenna has no coverage.  Which does you no good.  

 

[Radioguy7268]

25+ Years ago, Motorola offered a low power Systel repeater that was just 2 watts, and was designed to offer repeater service combined with telephone interconnect for small warehouses, retirement homes, and factories. Inside the box, it was just 2 GP300 portables, a controller, and cooling fans.

They worked, but they didn't last. Most got replaced within 5 years with a "real" repeater.

I'll repeat what was said above. A duplexer saves you time, trouble, and money. If you're going to use a split antenna system, you're still going to need cavity filters to make it work properly. Unless you've already got the 2 antennas, the double lengths of coax, and the cavity filters, you're spending more money just to "save" on a duplexer.

A properly tuned duplexer "eats" less than 2dB for a UHF system with a 5 MHz split. If you've been paying attention here, you should know that transmit power out is not the limiting factor in most repeater systems. People chase transmit power because they think it's what makes a repeater better. Balance is what makes a repeater system better. Duplexers provide balance.

[gortex2]

We have 2 repeaters for our SAR group based on portables. Both use modified ICOM handhelds (Swapped MX antenna jack for BNC Jack from ham radio. I used a very small duplexer made for 15 watts or less. They are controlled with a vox style controller that plug into the mic jacks. Battery eliminators on all radios with a 3AH Gel Cell mounted in the pelican case. VHF is 2.3 watts out to the antenna on high power. UHF is 3 watts out to the antenna. They work as intended but if they sold the RT97 at the time I would have ordered it. 

Both are in a small pelican case. That was part of our use case. We have a portable mast with 25' of LMR400 and Unity Gain antenna for each. 2 guys can walk up a trail with the case, antenna and cable and set it up on a hill to give us that extra range. It doesn't get used all the time, but the location it was built for works well. We are primarily VHF so the power is not perfect but is better than hauling our big repeater up to a site with a 6 wheeler. The UHF has only been used for training. Works good, but as said if I had the RT or Midland option at that point I would have gotten those. 

In the end we have about $1000 per Pelican Case. The radios were purchased on state contract for $299 each, Duplexer was $100, repeater controller was 100 and another $200 in battery, RF jumpers, bulkhead mount and charger for battery. We went with the ICOM LMR radio because we use public safety band, and to be honest they are way better than any CCR you will try. The receiver on the ICOM is very hot and is very narrow to the band in use.

[SteveShannon]

4 hours ago, gortex2 said:

We have 2 repeaters for our SAR group based on portables. Both use modified ICOM handhelds (Swapped MX antenna jack for BNC Jack from ham radio. I used a very small duplexer made for 15 watts or less. They are controlled with a vox style controller that plug into the mic jacks. Battery eliminators on all radios with a 3AH Gel Cell mounted in the pelican case. VHF is 2.3 watts out to the antenna on high power. UHF is 3 watts out to the antenna. They work as intended but if they sold the RT97 at the time I would have ordered it. 

Both are in a small pelican case. That was part of our use case. We have a portable mast with 25' of LMR400 and Unity Gain antenna for each. 2 guys can walk up a trail with the case, antenna and cable and set it up on a hill to give us that extra range. It doesn't get used all the time, but the location it was built for works well. We are primarily VHF so the power is not perfect but is better than hauling our big repeater up to a site with a 6 wheeler. The UHF has only been used for training. Works good, but as said if I had the RT or Midland option at that point I would have gotten those. 

In the end we have about $1000 per Pelican Case. The radios were purchased on state contract for $299 each, Duplexer was $100, repeater controller was 100 and another $200 in battery, RF jumpers, bulkhead mount and charger for battery. We went with the ICOM LMR radio because we use public safety band, and to be honest they are way better than any CCR you will try. The receiver on the ICOM is very hot and is very narrow to the band in use.

I’d love to see pictures and an actual parts list.  

[gortex2]

I'll have to dig for final pictures but here was the pictures from our "trial" unit. Pretty much all is the same other than we replaced the connectors on the ICOM with BNC (it was an orderable part from them) vs the adapter we used on this unit. For this one that was VHF that basically the only change we made. The UHF has a similar duplexer but in silver. That really the only way to know them apart without turning on the radios. I'd have to dig for the parts list as this was done back in 2013. 

 

[SteveShannon]

Cool, thanks!  That's good enough; you don't need to dig for a BOM.

 

[WRUH396]

Very cool pics Gortex2!  Thanks.

935, yeah the reasons or issues you brought up are the exact reasons I believe the 'test-runs' I have seen on YouTube seem to fail miserably.  However 5 MHz of separation seems ample to allow for a two antenna system.  I have had success on two antenna systems even down on 2-meters which only has 600KHz separation instead of 5.  I am just banging ideas around.  I do have a quite successful homebrew repeater up but love messin' around and like to see what others have done or where their experiments failed.  

The radios are so cheap I think I will give it a try.  I should have no problems providing 30'+ of physical separation and since the location I am looking at is located at the South end of a long valley I am thinking I will try with Yagis since two you can pick up two decent Yagi antennas for nearly the same price as a single 1486s and with the majority of the gain aimed to the valley it seems like it may work even without the duplexer.  I do wonder though, if I will need to put the cheap radios in separate metal boxes and maybe even separate those with the choked cross-connect audio cables.     

 

[gortex2]

17 hours ago, Sshannon said:

Cool, thanks!  That's good enough; you don't need to dig for a BOM.

 

Good deal. Since then we have built one in a similar size case with 2 20 watt vhf mobiles set for 15 watts. Additionally we have another in a Big Box with 45 watt mobiles and a huge VHF duplexer (Sinclair) but with 4 35amh batteries takes a 6 wheeler and a small army to setup. We only use this unit on one event thru out the year and it covers a large area. 

[SteveShannon]

1 hour ago, gortex2 said:

Good deal. Since then we have built one in a similar size case with 2 20 watt vhf mobiles set for 15 watts. Additionally we have another in a Big Box with 45 watt mobiles and a huge VHF duplexer (Sinclair) but with 4 35amh batteries takes a 6 wheeler and a small army to setup. We only use this unit on one event thru out the year and it covers a large area. 

I’ve got one of those 18”x18”x18” all-weather equipment boxes with an extending handle and wheels. I wish it had larger tires so I could tow it behind me while hiking up a hill at our rocket launch site.  I also have lots of SLA 7Ah batteries I’d like to use.  They’re heavy-ish but that would be mitigated by being able to roll the case behind me. I haven’t done the calculations but I think I’d only need a couple for a Retevis RT97S. Most of the time it will simply be receiving with maybe 5 or 10 minutes of transmitting max.

I’ve toyed with doing something like you did using the two Radioddity DB20G mobiles I bought last month, but it would probably end up costing nearly as much as a Retevis RT97S.