BUDGET - RF AMPLIFIER (AM FM SSB) 3-30 MHZ(Not a Recommended Device )

ILEGAL TO USE ON CB.
CHECK SIGNAL BEFORE YOU TRANSMIT STAY LEGAL !!
ALIEXPRESS LINK
s.click.aliexp...
SPECIFICATIONS
Frequency range 3-30MHz
Power supply voltage 12-14V
Input current 14-20A
Input power 3-5W
Single sideband input power 2-10W
FM output power Maximum output 100W
AM output power Maximum output 200W
Single sideband output power Maximum output 300W
Working mode FM- AM-CW-SSB
Fuse blown 2×12A
Size 120 × 225 × 38mm
Weight 750g
I RECOMMEND USING A LPF
www.allaboutci...

[@9V1SA]

Got one of these: building a box of stuff around it to make it useable as it needs a) output filtering (has absolutely no LPF as supplied) and b) it needs matching on the input (eg 3dB attenuator) to avoid presenting unreasonable SWR to the driving rig. I am undecided whether going for a QRP rig and adding something like this is a good idea. I have definitely learned a lot but it’s a big faff to get it legal and frankly buying something like a FT-891 or an IC-7300 would have given me more reliability, more functionality, and stuff like SWR protection which this does not have for not much more money at the end of the day. If you search on TH-cam for BJ-300 there are some Spanish speaking hams who go through how to mod it and the translated subtitles are good enough to see what they are doing.

[@HamTechRadioScannerDrones]

Agree i will send it back or sell

[@JimCoupeTQ]

Works great for me on CB.. SSB.. Gives me around 120W on my antenna.

[@HamTechRadioScannerDrones]

Not bad

[@Marcink126]

It is not designed to work with SSB modulation (it is a lie in the amp description on aliexpress). It is class C amp. So only FM modulation, eventually AM.

[@johnyum9021]

Hi jim do u work it in ssb mode some comments say it doesn't work or work well in ssb because I gonna to buy one

[@Marcink126]

@@johnyum9021 from the box it does not work well in SSB mode. You need to add transistors bias circuit.

[@JamminJerseyRocker]

BUYER BEWARE! I purchased 2 of the BJ-300 Plus (same amp but includes fan on top). First issue, Hi /Low switch is backwards on both amps: Hi is Low Power, Low is Hi Power, Modulation is garbled and the amp reflects about 6 watts back into radio. My SWR is 1.1 to 1. Transmits noise at dead key. 3-4 watts in brings about 160 watts out in AM but reflects back about 6 watts and screws up your SWR big time! Avoid this amp and get an RM Italy version. Save yourself some grief!

[@HamTechRadioScannerDrones]

Agree

[@alanreader4815]

in the 80's used to be called a Burner.

[@HamTechRadioScannerDrones]

Yes remember

[@mkaylor]

WIll be very interested in the outcomes. I was considering on of these for a Hermes Lite 2. I want something between 300 and 500 watts without breaking the bank.

[@HamTechRadioScannerDrones]

Hope this helps you decide .

[@HarishKottayam]

I got one, but swr spikes like anything 😢 no clue on why its happening..

[@HamTechRadioScannerDrones]

These amps are no good ,

[@HarishKottayam]

@@HamTechRadioScannerDrones yeah , really

[@kishor_VU2MZT]

Do you tested it ,for modulation and output power ?

[@HamTechRadioScannerDrones]

I need more filtering first to stop spurious.

[@davidbrowne1588]

Hi , what are you going to use for LPF for each band ?
Dave 2E0DMB

[@HamTechRadioScannerDrones]

Hi , this was a quick unbox which one do you recommend ?

[@ikkeikke4561]

Using it for years, 5 watt ssb in 120 out..

[@HamTechRadioScannerDrones]

Thanks what bands

[@mkaylor]

So it doesn't do the advertised 300W SSB? Expected!

[@NateClark-x4w]

@@mkaylor In order to get 300watts out, you have to put 10 watts in.

[@F_Tim1961]

@@NateClark-x4w Rubbish. It's a linear amp. If the first poster is correct and I suspect he is then you'd only get 240 W out but it would likely go into compression and you'd be lucky to get 200 W PEP. All RM amps are notorious for having model numbers that are about 2x the maximum PEP out , wit the case glowing hot. Some models of this BJ 300 are sold with a top mounted cooling fan which is an indication that the thermal design is marginal. These cheap HF amps generally use new old stock bipolar RF transistors that can 't be had in one off lots for repair use.

[@mrtechie6810]

How about the RM Italy amps? Do any of the cheaper ones have low pass filters?

[@HamTechRadioScannerDrones]

Sorry I never use it .

[@Marcink126]

They dont.

[@sickcyber]

Can you use it 88-108 mhz in fm mode? Because I thought fm was higher than 3-30 mhz

[@HamTechRadioScannerDrones]

Hi sorry I returned the unit

[@Marcink126]

No it is only 30MHz max.

[@jairusbaguio4219]

What is the RF transistor they used for BJ-300?

[@HamTechRadioScannerDrones]

No idea

[@NateClark-x4w]

@@HamTechRadioScannerDrones Mine has two Motorola MRF247 transistors.

[@F_Tim1961]

@@NateClark-x4w for my interest I looked this part up using the NJ Semiconductor website. It turns out that it is rated at 75 W in class C at 175 Mhz. So a two transistor push pull design would be doing well to produce 110 W out as an SSB amp as they have to be derated for linear bias. The Gpe is given as only 8dB. That suggests the Gpe of the MRF247 rises enormously as the frequency is taken down to 20 Mhz nominal otherwise the as found SSB/CW powr out found by reliable ?? reports would simply be impossible . There's likely no MFR test data to verify that.
The biggest disadvantage of these is that they have to have an external 150 W pep capable filter set added on . There are basically zero kits or made up RF filters that can handle this sort of power. One exception - Far Circuits in Chicago sells a board only based on an old ARRL design that is good for 250 W or so. The passive parts can be had from Kits and parts in FL (Toroid king). JUst an observation , no commercial interest. I'd be checking on how much replacement MRF247s cost and even if they could be found , before I started doing a lot of re-engineering on it.