Dummy loads

[ergbert]

I'm in the middle of transitioning my megaspot (STM32DVM + Tait TM8105 VHF transceiver) to a homebrew repeater setup using two UHF Motorola CDM's... a 40W CDM750 for the TX radio, and a 25W CDM1550 for RX. For testing purposes, I'm setting the power as low as possible, and plan to put a dummy load on the duplexer output. Will this still allow me to work the repeater from on my suburban lot, or will the dummy load soak up everything? I don't want to splatter RF all over the neighborhood while I'm testing, but I do want to be able to interact with it via HT from the garage or similar.

The previous setup used a HT antenna (Signal Stick on a BNC 90º connector), but that worked OK because the Tait was able to be set for a TX output of 1W. The CDM's seem to be a bit less configurable in some respects.

 

[WA0CBW]

Depends on the shielding of your dummy load but most likely it would work, maybe farther than you would like.
Bill

 

[jonwienke]

A dummy load will work, your range will be reduced to roughly rock-throwing distance.

 

[ergbert]

Thanks, that's about as far as I want it to get out, until I've got a solid configuration nailed down.

 

[kayn1n32008]

I'm in the middle of transitioning my megaspot (STM32DVM + Tait TM8105 VHF transceiver) to a homebrew repeater setup using two UHF Motorola CDM's... a 40W CDM750 for the TX radio, and a 25W CDM1550 for RX.

Swap the TX and RX radios. Use the 25w radio for Tx. The 45w and 25w radios have the same chassis. The 25w radio can be dropped to something like 5 watts. You will easily be able to work your repeater from all around your lot. Another option would be to put a HT antenna on the RX radio and a dummy load on the TX radio.

 

[ergbert]

Swap the TX and RX radios. Use the 25w radio for Tx. The 45w and 25w radios have the same chassis. The 25w radio can be dropped to something like 5 watts. You will easily be able to work your repeater from all around your lot. Another option would be to put a HT antenna on the RX radio and a dummy load on the TX radio.

I noticed the 45W radio can only go down to 20W... I honestly just got the 25W in my hands and have not read it yet. Swapping seems to be the way to go, thank you.

As for putting an HT antenna on the RX radio and dummy load on the TX radio, what will that do for me? I have a Sinclair duplexer that I’m going to be using...

Trying to be a good neighbor and all...

 

[TampaTyron]

As said above, use the lower powered radio as the TX and get it down as low as possible. If you can not get it low enough, use the dummy load you intended. If you want the dummy load to go a bit further, you can add 6-10ft of RG58 and run the cable up higher or in the direction of the coverage you want to extent to. The main effect is leakage from the cable both coming from the cable to your radio and from your radio through the cable to the repeater. TT

 

[kayn1n32008]

I noticed the 45W radio can only go down to 20W... I honestly just got the 25W in my hands and have not read it yet. Swapping seems to be the way to go, thank you.

As for putting an HT antenna on the RX radio and dummy load on the TX radio, what will that do for me? I have a Sinclair duplexer that I’m going to be using...

Trying to be a good neighbor and all...

It will allow for a solid receive signal at your repeater, the dummy load keep it from going very far. You will likely get 500 to 1000m radius over open terrain even with a dummy load.