VCO output dropping

Thread Starter

@Pra

Joined Sep 9, 2021
6
Am using VCO (POS-400+) to generate a fixed 300MHz signal.
This VCO output is connected to an Attenuator (ZX73-2500+ ) and the attenuator output is further fed to a RF Amplifier (ZHL-1-2W+) all with supporting electronics for controls.
This has been working fine. (all components are Mini-Circuits make)

Now, my application demands that: I use that same VCO output signal (300MHz) to feed to another attenuator (in parallel to the above) and another RF amp (ZHL-1-2W) is connected to the output of this second attenuator.

ISSUE:
While I am connecting in this mode, the output of the second RF amplifier is heavily dropping to ~10% of its normal expected output while the original RF amp drop is marginal. As I realized, this is due to the VCO output itself is dropping.

QUERY:
1) Is there an issue in the design ?
2) Any remedies/corrections recommended viz: matching issues?
3) What could be the reason for this drop in signal & how to correct it?

Please provide technical help or recommend suitable help centers/ websites.
Thanks.
 

DickCappels

Joined Aug 21, 2008
7,985
1. Yes, you are hoping to get more power than the VCO is meant to deliver.
2. Please see below.
3. The VCO only generates a certain amount of power. If you divide the power up among multiple loads, the voltage should drop.

The VCO only generates a certain amount of power. If you divide the power up among multiple loads, the voltage should drop. If mini-circuits offers an active splitter that may be the solution, otherwise, a splitter followed by amplifiers would be a fall-back position.

Note: I am no longer familiar with the mini-circuits product line, but decades ago I thought they were tops.
 

Radio Head

Joined Sep 10, 2021
1
Am using VCO (POS-400+) to generate a fixed 300MHz signal.
This VCO output is connected to an Attenuator (ZX73-2500+ ) and the attenuator output is further fed to a RF Amplifier (ZHL-1-2W+) all with supporting electronics for controls.
This has been working fine. (all components are Mini-Circuits make)

Now, my application demands that: I use that same VCO output signal (300MHz) to feed to another attenuator (in parallel to the above) and another RF amp (ZHL-1-2W) is connected to the output of this second attenuator.

ISSUE:
While I am connecting in this mode, the output of the second RF amplifier is heavily dropping to ~10% of its normal expected output while the original RF amp drop is marginal. As I realized, this is due to the VCO output itself is dropping.

QUERY:
1) Is there an issue in the design ?
2) Any remedies/corrections recommended viz: matching issues?
3) What could be the reason for this drop in signal & how to correct it?

Please provide technical help or recommend suitable help centers/ websites.
Thanks.
You don’t mention att values used.
Try a splitter, rather than two parallel att.s.
 

pravardhan

Joined Jul 30, 2009
10
Hi,

First of all I am not an RF expert but I have worked on a few PLL synthesizer.

You can try 2 options:
1. Use an Balun or an Coupler from Mini-Circuit with same impedance. Splitter may also work.
2. How about tapping the VCO signal after the amplifier?

Also how much power (dBm) will both of the devices require from the VCO output? The part you mentioned (POS-400+) provides +9dBm typical output as per the datasheet.

Also check for any impedance mismatch between the VCO and the devices your want to use.

Bye,
Pravardhan U.S
 

Thread Starter

@Pra

Joined Sep 9, 2021
6
1. Yes, you are hoping to get more power than the VCO is meant to deliver.
2. Please see below.
3. The VCO only generates a certain amount of power. If you divide the power up among multiple loads, the voltage should drop.

The VCO only generates a certain amount of power. If you divide the power up among multiple loads, the voltage should drop. If mini-circuits offers an active splitter that may be the solution, otherwise, a splitter followed by amplifiers would be a fall-back position.

Note: I am no longer familiar with the mini-circuits product line, but decades ago I thought they were tops.
Thanks DickCappels.
You are right. I am drawing more power from the VCO and thus that leads to the drop in RF power.
The splitter is a good suggestion. I have to try.

In the meanwhile, I fed the VCO output to an OPAMP HFA1145 hoping to see if it helps. Unfortunately no improvements.
 

Thread Starter

@Pra

Joined Sep 9, 2021
6
Echoing DickCappels. Minicircuits have a large selection of two way splitters available:
https://www.minicircuits.com/WebStore/Splitters.html?

You will need to compensate for the splitter insertion loss in your attenuator value calculation.

Here is a link to minicircuits application note on splitters:
https://www.minicircuits.com/appdoc/AN10-006.html

I am not affiliated to minicircuits
Thanks Kiwiboy.
I am considering Splitters as a solution to the problem as all the experts are suggesting..... but need to find one quick and easily available.
 

Thread Starter

@Pra

Joined Sep 9, 2021
6
You don’t mention att values used.
Try a splitter, rather than two parallel att.s.
Thanks Radio Head.
I am using ZX73-2500-S as the Attenuator/s.
Attenuators used are voltage varaible type and is needed to control the Gain of the latter RF ampr.
 

Thread Starter

@Pra

Joined Sep 9, 2021
6
Hi,

First of all I am not an RF expert but I have worked on a few PLL synthesizer.

You can try 2 options:
1. Use an Balun or an Coupler from Mini-Circuit with same impedance. Splitter may also work.
2. How about tapping the VCO signal after the amplifier?

Also how much power (dBm) will both of the devices require from the VCO output? The part you mentioned (POS-400+) provides +9dBm typical output as per the datasheet.

Also check for any impedance mismatch between the VCO and the devices your want to use.

Bye,
Pravardhan U.S
Thanks Pravardhan.

Also how much power (dBm) will both of the devices require from the VCO output? The part you mentioned (POS-400+) provides +9dBm typical output as per the datasheet.

Replying.....: I am using ZX73-2500-S+ as the attenuators . The datasheet mentions that these require 20dBm Input power. So my query is if using Splitter then will the POS- 400+ be able to provide to two Attenuators the required power???

Am I right in thinking so???
 
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