Pre-amp upgrade?

[prcguy]

Is the current preamp mounted at the antenna or near the radios? If at the radios, what kind of coax and how much? Placing the preamp at the antenna will improve system noise figure by about the amount of your coax loss.

 

[kb5udf]

Current preamp was acquired after I got the antenna up on the tower, so its in the shack before the splitter. Coax is RG11
with a 75->50ohm coupler that came with the pre-amp that at got for cheap on a fleabay auction.

The run is <100 feet, I forget if I just got a 100 foot run or an 80; probably an 80.

The current plan is, acquire the new preamp deploy in shack initially, and if it does not worsen or at least improves my reception, then I will
install it up the tower at the antenna. That will be a bit of work as you are no doubt aware: climbing up, unbolting mounting arm, unsealing the connection to antenna, running jumpers etc. resealing remounting. It may be I can do all the work without dismounting antenna, but probably not given the current way its mounted.

I'm no electrical engineer, but I am floating the following in lieu of a bias-t setup to power a remote pre-amp: get a run of wire of appropriate length and calculate the voltage loss related to this, and simply run the voltage in the shack up the wire to the pre-amp on tower that will give me nominal 5 volts at the end of the run.

Good idea, bad idea?

 

[prcguy]

Current preamp was acquired after I got the antenna up on the tower, so its in the shack before the splitter. Coax is RG11
with a 75->50ohm coupler that came with the pre-amp that at got for cheap on a fleabay auction.

The run is <100 feet, I forget if I just got a 100 foot run or an 80; probably an 80.

The current plan is, acquire the new preamp deploy in shack initially, and if it does not worsen or at least improves my reception, then I will
install it up the tower at the antenna. That will be a bit of work as you are no doubt aware: climbing up, unbolting mounting arm, unsealing the connection to antenna, running jumpers etc. resealing remounting. It may be I can do all the work without dismounting antenna, but probably not given the current way its mounted.

I'm no electrical engineer, but I am floating the following in lieu of a bias-t setup to power a remote pre-amp: get a run of wire of appropriate length and calculate the voltage loss related to this, and simply run the voltage in the shack up the wire to the pre-amp on tower that will give me nominal 5 volts at the end of the run.

Good idea, bad idea?

Using a bias T is so much easier and it has some built in DC filtering. Running external wires will be subject to picking up lots of RFI and feeding that right into the preamp as I suspect the DC input of the little Minicircuits amp doesn't have a very elaborate RF bypass.

Here is a bias T that I was going to stock up on as they are cheap, shielded and handle a reasonable amount of current.

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[kb5udf]

Ordered, thanks. If am ever near where you are prcguy, I'll buy you a very large steak.

 

[kb5udf]

Hmm. Ok I ordered it but then realize how to use this, it looks like I need something else? That is, if I deploy this device RF bias Tee in the shack, what do I need up the tower with the preamp to get the dc off the coax to the preamp?

 

[prcguy]

Hmm. Ok I ordered it but then realize how to use this, it looks like I need something else? That is, if I deploy this device RF bias Tee in the shack, what do I need up the tower with the preamp to get the dc off the coax to the preamp?

A second bias T in reverse.

 

[kb5udf]

DOHH, (on me of course).

I owe you a steak and a drink now.

 

[prcguy]

DOHH, (on me of course).

I owe you a steak and a drink now.

Don't make me shop for plane tickets.....

 

[Ubbe]

Doesn't many preamps have voltage regulators to a 3,5V circuit or a 5V one that can handle voltages up to 15 volts or more? If you run the preamp circuit from the raw voltage you feed the bias-T it will be very suspectable to oscillation and feedback issues, and by using a voltage regulator you probably also filter out all RF.

Absolutely test everything first at the receiver end to see that there are no issues and do use a variable attenuator with the finished solution to set the best S/N you can get by the exact amount of attenuation, that probably can be improved on by EQ the gain and adding external filtering.

/Ubbe

 

[kb5udf]

Yes Ubbe a will do my best to test the system. So have a few filter options a use after the spitter including
for civil and military air.

 

[prcguy]

Doesn't many preamps have voltage regulators to a 3,5V circuit or a 5V one that can handle voltages up to 15 volts or more? If you run the preamp circuit from the raw voltage you feed the bias-T it will be very suspectable to oscillation and feedback issues, and by using a voltage regulator you probably also filter out all RF.

Absolutely test everything first at the receiver end to see that there are no issues and do use a variable attenuator with the finished solution to set the best S/N you can get by the exact amount of attenuation, that probably can be improved on by EQ the gain and adding external filtering.

/Ubbe

In the few cases where I used a 5v preamp at the antenna I did send 12v up the coax and used a 3 pin linear regulator at the preamp to get 5v. That was partially because I had other 12v items in the remote box and it makes it less critical compensating for voltage drop as some 5v equipment can be very voltage sensitive.

 

[kb5udf]

All the US distributors are OOS.

Is this to a chinese seller possibly legit? I suspicious given it does not say mini circuits on the product.

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