very odd


militaryoperator
 

OK, So, thinking on 6cm I'd thought I'd see whats in the parts box. 

So, OHM near and can hear on 9 so 6 should be ok. Some sort of pre amp then mix and see if I can hear on my RSP2.
I have one of these little Chinese amps, 50-4000 5v etc, thought I'd try it. Set sig gen at 1920 (1/3rd) and can see 5760 on speccy. 

So, inserted little board, switched on, nil. Blast I thought. But, I noticed as I switched off the 5v to it the o/p shot up then fell away. Adjusting the volts going board at 1.3v I get big sig out, first pic. Switch off I get nowt, second pic.

Direct from sig gen to speccy I have to increase the 1920 by about 15db to get a small blip on speccy at 5760, pic 3. 

So, how is this little amp working fine at just 1.3v ?????

What am I missing or getting confused about?

Ben


Mark GM4ISM
 

Hi Ben

 I have a couple that behave similarly, probably from the same source.

 The devices in mine  by design need have  no dropper resistor to limit the current, they are supposed to be self biasing at 5V and draw the rated current

The devices are 'defective' in mine.   You do get  most of the required gain if you externally limit the current to the device rating, but the P1dB suffers badly

 I replaced the devices with full spec ones


 Check the current as you raise the supply volts.  Stop when you reach the device rated current.  Running at 5V is likely to cause the devices to pop.

Regards

Mark GM4ISM

 


On 06/05/2021 15:33, militaryoperator via groups.io wrote:
OK, So, thinking on 6cm I'd thought I'd see whats in the parts box. 

So, OHM near and can hear on 9 so 6 should be ok. Some sort of pre amp then mix and see if I can hear on my RSP2.
I have one of these little Chinese amps, 50-4000 5v etc, thought I'd try it. Set sig gen at 1920 (1/3rd) and can see 5760 on speccy. 

So, inserted little board, switched on, nil. Blast I thought. But, I noticed as I switched off the 5v to it the o/p shot up then fell away. Adjusting the volts going board at 1.3v I get big sig out, first pic. Switch off I get nowt, second pic.

Direct from sig gen to speccy I have to increase the 1920 by about 15db to get a small blip on speccy at 5760, pic 3. 

So, how is this little amp working fine at just 1.3v ?????

What am I missing or getting confused about?

Ben

Virus-free. www.avg.com


militaryoperator
 

Hi Ben
 I have a couple that behave similarly, probably from the same source.
 The devices in mine  by design need have  no dropper resistor to limit the current, they are supposed to be self biasing at 5V and draw the rated current
The devices are 'defective' in mine.   You do get  most of the required gain if you externally limit the current to the device rating, but the P1dB suffers badly
 I replaced the devices with full spec ones

 Check the current as you raise the supply volts.  Stop when you reach the device rated current.  Running at 5V is likely to cause the devices to pop.
Regards
Mark GM4ISM
 
I dont know what the device is, it has a little metal cover over but certainly works at 1.3v, hi. 

Ben 


Mark GM4ISM
 

Ben mine are labelled

SPF5189Z

F=50-400MHz

Voltage = 5V


lookup the specs for SPF5189Z 

it needs 90mA


Mark

On 06/05/2021 15:52, militaryoperator via groups.io wrote:
Hi Ben
 I have a couple that behave similarly, probably from the same source.
 The devices in mine  by design need have  no dropper resistor to limit the current, they are supposed to be self biasing at 5V and draw the rated current
The devices are 'defective' in mine.   You do get  most of the required gain if you externally limit the current to the device rating, but the P1dB suffers badly
 I replaced the devices with full spec ones

 Check the current as you raise the supply volts.  Stop when you reach the device rated current.  Running at 5V is likely to cause the devices to pop.
Regards
Mark GM4ISM
 
I dont know what the device is, it has a little metal cover over but certainly works at 1.3v, hi. 

Ben 

Virus-free. www.avg.com


militaryoperator
 

Ben mine are labelled
SPF5189Z
F=50-400MHz
Voltage = 5V

lookup the specs for SPF5189Z 
it needs 90mA

Mark

Yes. That's the number, I thought it was just a model number

At 1.3v its taking 15ma. If I increase the volts the o/p falls away. 

I'll try it into a mixer with an ADF osc as lo and see if I can hear/see anything of OHM on my RSP2.

Ben.


Neil Smith G4DBN
 

On 06/05/2021 16:12, militaryoperator via groups.io wrote:
At 1.3v its taking 15ma. If I increase the volts the o/p falls away.
Ben, is it possible it is going into oscillation on some wildly out of band frequency above 1.3 V and that is what is causing the loss of signal?

Neil G4DBN


militaryoperator
 



> At 1.3v its taking 15ma. If I increase the volts the o/p falls away.


Ben, is it possible it is going into oscillation on some wildly out of
band frequency above 1.3 V and that is what is causing the loss of signal?

Neil G4DBN



No. I think its just a bit of crap Neil. 

I just tried one of those supposed 1W amps, nice heatsink, driven fully from sig gen at 2.4 its taking 100ma at 5v so just 1/2watt i/p, chip is not even getting warm, heatsink a total overkill. 


Is everything from China rubbish?

My own fault for buying the rubbish I guess. 

Ben.  


Alan Melia
 


Hi Ben , just in aswer to your question......No not everything from China is rubbish, but there is a lot .It is often so cheap you have to either take a chance and black mark the poor sellers. I have several units, two  nanoVNAs, a computing counter timer (FS-2  I think Neil has one), but you have to be careful with eBay sellers. I must say though that most of the bits I have bought have been recommended. there are one or two names getting a good reputation.but you have to watch were there are severalsellers of the same item dont select the cheapest look at them in comparison with what ancilliaries they provide. I think large quantites of the pcbs are made available and there is  race assembling them for the lowest cost. you will often see 2:1 or even 3:1 variation range in prices.
 
Several UK microwavers I have noticed bought modules expecting to remove the main chip and replave it with a good one bought locally..........because it was cheaper that getting a small quantity of pcbs made.
 
The SMAs I stock are from China but bought direct from a company that I now trust. There are not comparable with Hooba and Sooner ( :-)) ) but they are adequate to 4GHz.
 
Alan
G3NYK
 

----- Original Message -----
Sent: Thursday, May 06, 2021 7:41 PM
Subject: Re: [UKMicrowaves] very odd



> At 1.3v its taking 15ma. If I increase the volts the o/p falls away.


Ben, is it possible it is going into oscillation on some wildly out of
band frequency above 1.3 V and that is what is causing the loss of signal?

Neil G4DBN



No. I think its just a bit of crap Neil. 

I just tried one of those supposed 1W amps, nice heatsink, driven fully from sig gen at 2.4 its taking 100ma at 5v so just 1/2watt i/p, chip is not even getting warm, heatsink a total overkill. 


Is everything from China rubbish?

My own fault for buying the rubbish I guess. 

Ben.  


Neil Smith G4DBN
 

Fingers crossed, apart from the ADF4351 boards that were a) dreadfully designed and b) had fake remarked ADF4350 chips, and a cheap signal source with an OLED screen that felt like a student project, I have been quite lucky with purchases from China.  I've bought microwave semiconductors from Aliexpress with 100% success, also many PA devices from UTSource (main store) and a few from Teng Da, plus my NanoVNAv2+4 from Tindie, an FA-2 reciprocal 8 GHz 11 digits/sec frequency counter and a WB-SG1 signal generator from Aliexpress.  I just bought some engraved degree rings 

Also bought a couple of DDS boards that are good. The only things that have been awful were via ebay.  Oh, I had an SMA to N adaptor that had more than 1dB loss at 9cm - takes some doing - and a load of crimp-terminated SMA patch leads on RG316 that just fell apart.  Those were bought from a UK rally and probably came from a terrible far eastern source.  If you stick with reputable suppliers in Shenzhen and HK, you can find good quality stuff. I have a Hermes Lite that turned up form Shenzhen in four days, and I've had LDMOS devices from HK arrive in under 30 hours.  Meanwhile, some bits from Farnell that were in stock have taken nine days to turn up.

Wherever possible, I only buy complete things from Chinese suppliers where the thing is designed by the ever-mysterious BG7TBL or appears to be home-grown, or is unavailable from the usual sources. I don't buy clones of things designed elsewhere unless they are specifically sponsored by the original designer. I am occasionally tempted to buy from LCSC when I can't find a thing from the usual UK/EU/US sources, but so far I've always found alternatives.  As the chip shortage really starts to bite, I might not maintain that clean record.

Neil G4DBN

On 06/05/2021 21:07, Alan Melia via groups.io wrote:

Hi Ben , just in aswer to your question......No not everything from China is rubbish, but there is a lot .It is often so cheap you have to either take a chance and black mark the poor sellers. I have several units, two  nanoVNAs, a computing counter timer (FS-2  I think Neil has one), but you have to be careful with eBay sellers. I must say though that most of the bits I have bought have been recommended. there are one or two names getting a good reputation.but you have to watch were there are severalsellers of the same item dont select the cheapest look at them in comparison with what ancilliaries they provide. I think large quantites of the pcbs are made available and there is  race assembling them for the lowest cost. you will often see 2:1 or even 3:1 variation range in prices.
 
Several UK microwavers I have noticed bought modules expecting to remove the main chip and replave it with a good one bought locally..........because it was cheaper that getting a small quantity of pcbs made.
 
The SMAs I stock are from China but bought direct from a company that I now trust. There are not comparable with Hooba and Sooner ( :-)) ) but they are adequate to 4GHz.
 
Alan
G3NYK
 
----- Original Message -----
Sent: Thursday, May 06, 2021 7:41 PM
Subject: Re: [UKMicrowaves] very odd



> At 1.3v its taking 15ma. If I increase the volts the o/p falls away.


Ben, is it possible it is going into oscillation on some wildly out of
band frequency above 1.3 V and that is what is causing the loss of signal?

Neil G4DBN



No. I think its just a bit of crap Neil. 

I just tried one of those supposed 1W amps, nice heatsink, driven fully from sig gen at 2.4 its taking 100ma at 5v so just 1/2watt i/p, chip is not even getting warm, heatsink a total overkill. 


Is everything from China rubbish?

My own fault for buying the rubbish I guess. 

Ben.  
_