Portable radio based repeater???

[WRQE264]

Hello, 

I am newer to GMRS and have some basic understanding of how radio transmissions work. I'm a little fuzzy on nomenclature when it comes to repeaters, but I understand the concept. 

I had wondered in my head if you'd be able to set up a portable radio based repeater. This would be something for like at the beach, campsite, event, etc.

In my internet wanderings I came across the following. Does anyone have any experience/thoughts/ideas they'd be willing to share. Seems like a lesser expensive idea to work out that doesn't cost an arm and a leg.

 

SR-628 Cross Band Duplex Repeater Controller with Cable Free Shipping - Walkie-Talkie Android Phone Two Way Radio (walkytalkyshop.com)

 

Thanks!

john

[OffRoaderX]

The English on that webpage is suspect, but that aside, it says this is for making a cross-band repeater (RX on UHF, TX on VHF or visa-versa) - that means that the two radios sitting next to each other would not be much of an issue. But if you set your radios to work as a GMRS repeater (RX on 467.xxx and TX on 462.xxx) there would be much desense (the radios making each other deaf because they are too close) unless you set them at least 10-15 feet apart... But I've never used something like this so I would like to see what anyone with experience has to say. 

Something like the Retevis RT97 would do exactly what you want, but it costs a bit more.

[KAF6045]

Content copied to thread in Technical...

[marcspaz]

 

I bought this exact unit from Amazon... I tried using it with two Baofeng handhelds.  Even though they call it cross-band, the radios actually determine if its same band or cross-band.

 

Bottom line... it ended up in the trash.  It relies on the volume level of the radio, VOX operation, and if you try to use it on the same band, unless you have incredibly expensive radios with great filtering on the front-end, the transmitter wipes out the receiver and it gets stuck in a transmit loop until you turn off either one of the two radios.

 

I am a geek by trade, so I ended up building a full-blown portable repeater.  At this point, I would recommend you just buy a pre-programed Retevis. 

[Blaise]

11 hours ago, marcspaz said:

 the transmitter wipes out the receiver and it gets stuck in a transmit loop until you turn off either one of the two radios.

I've been reading about antennae rather a lot lately to try to understand this exact issue.  I assure you I believe myself to be nothing remotely like well informed on this topic, but from what I'm reading, it seems like this has multiple possible solutions:

• If you separated the two antennae with a metal sheet about 5 degrees wide to each antenna, you would have a dead spot on a narrow line (which might be made up for at distance by reflection/diffraction), but the bulk of the transmitted energy would miss the receiving antenna, and lessen or eliminate the problem.
• If you mounted the two antenna colinearly one above the other, maybe also with a metal disc separating them, you could solve the problem similarly with no dead spot at all.

Please help me understand how I am wrong!  (I assume I'm wrong, since no one else said it...)
 

[SteveShannon]

59 minutes ago, Blaise said:

I've been reading about antennae rather a lot lately to try to understand this exact issue.  I assure you I believe myself to be nothing remotely like well informed on this topic, but from what I'm reading, it seems like this has multiple possible solutions:

• If you separated the two antennae with a metal sheet about 5 degrees wide to each antenna, you would have a dead spot on a narrow line (which might be made up for at distance by reflection/diffraction), but the bulk of the transmitted energy would miss the receiving antenna, and lessen or eliminate the problem.
• If you mounted the two antenna colinearly one above the other, maybe also with a metal disc separating them, you could solve the problem similarly with no dead spot at all.

Please help me understand how I am wrong!  (I assume I'm wrong, since no one else said it...)
 

What you’re describing is necessary as well, unless you use a duplexer, but that’s for the antennas.  You still need to shield the circuitry of the transmitter from the circuitry of the receiver.  If you look inside a repeater, even the little Retevis 97, you’ll see that the transmitter and receiver are separated from each other within their own metal sealed compartments.

Edited October 4, 2022 by Sshannon
Added web photo showing internal construction of RT-97

[marcspaz]

@Blaise... I don't know that the shield concept wouldn't work. The question would be, how much would it impact the receiver or the transmit SWR. I don't know if it would work well, even if the transmit loop is stopped.

 

Something I think may happen is, the metal would act like a reflector and you would end up making a 2 element beam, instead. LoL 

 

Anyway, with two handheld radios, it wasn't worth the effort to try to remedy the issue. While building a quality repeater was significantly more expensive, I like it better for a bunch of reasons. 

[KAF6045]

10 hours ago, marcspaz said:

Something I think may happen is, the metal would act like a reflector and you would end up making a 2 element beam, instead. LoL

Possibly even worse -- two beams: receive from one direction, send 180 degrees opposite.

[BoxCar]

If you are playing with parasitic radiators (metal reflectors) then the distance between the antenna and the reflector is key. The distance between the two determines if the reflected wave adds or subtracts from the primary.

[marcspaz]

1 hour ago, KAF6045 said:

Possibly even worse -- two beams: receive from one direction, send 180 degrees opposite.

 

7 minutes ago, BoxCar said:

If you are playing with parasitic radiators (metal reflectors) then the distance between the antenna and the reflector is key. The distance between the two determines if the reflected wave adds or subtracts from the primary.

 

You have both renewed my faith in man.  LOL

[WRUR259]

Two Leixen UV-25D’s in ammo cans with cheap UT-72 antennas 40+ feet apart could work pretty well for a lower cost portable solution. Set everything to low power but the final output, which pushes close to 20 watts. 
Not that I would advocate such a thing.
 

 

[gortex2]

The Leixen UV-25D is not a GMRS certified radio.

Secondly from what I find online (ebay) the radio sells for around $100-125. Add in ammo can's, repeater controller, cables  and 2 $35.00 antennas adapters and such and your not far from the cost of a RT97. 

 

[WRUR259]

3 hours ago, gortex2 said:

The Leixen UV-25D is not a GMRS certified radio.

 

Hence, I don’t advocate for it. However, theoretically one could use the cross band repeat function on one radio to receive GMRS high, then transmit say, a low powered MURS signal to the other radio (cross banding as well) which would in turn transmit a higher powered GMRS low output. Not saying it’s kosher, just relatively cheap and effective. Can be done for under $300 with higher output.
 

Again, I do not advocate for running this type of setup.

[MichaelLAX]

Last I checked, Ham isn't kosher, either! 

Why don't you check and see if there is trademark availability for your repeater setup: THE MOONSHINER! 

[WRUR259]

I just started a thread on this concept if you want to check it out. It might make for interesting conversation.

On 10/5/2022 at 11:21 AM, MichaelLAX said:

Last I checked, Ham isn't kosher, either! 

Why don't you check and see if there is trademark availability for your repeater setup: THE MOONSHINER!