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TRU RPG-20 TX

H

HiTower

Guest
Hi. Is anyone familiar with the RPG 20 Low Power AM Transmitter by TransmittersRUs.com

http://www.transmittersrus.com/tru_rpg20.htm

Supposedly it is adjustable from 100mW to 20W

This would be great for a campus station perhaps, but how well does it perform? Is it a winner? or is it going to blow right away?

Thanks!
 
> Hi. Is anyone familiar with the RPG 20 Low Power AM
> Transmitter by TransmittersRUs.com
>
> http://www.transmittersrus.com/tru_rpg20.htm
>
> Supposedly it is adjustable from 100mW to 20W
>
> This would be great for a campus station perhaps, but how
> well does it perform? Is it a winner? or is it going to
> blow right away?
>
> Thanks!
>

I've been using one for a couple of years, works nice, sounds good too. Get a 13.8v supply from ratshack to run it. Be aware, though, that the 20W rating is PEAK, so the real rating is 5W average max. (you might squeeze up to 8W avg out of it, with symmetrical modulation clipping, though I'd put a fan on the rear heat sink if you go above 5W). Otherwise at 5W it has positive headroom for 125% or more modulation. Also appears to employ some soft negative peak clipping. It has SWR protection/indicator, which can trigger on high-frequency audio passages if your antenna bandwidth is too narrow. Since I'm padding it down with a switchable attenuator to (near) P15 levels during the day anyway (a bit more power at night to overcome noise!) I use a series 24 ohm resistor in the antenna tuning unit to broadband the system and stabilize the load to about 50 ohms, which solved the SWR problem (also chews up another 3db, which figures into the overall attenuator equation). The unit is adjustable via a front-panel knob from near zero to beyond full rated power but I find that the modulation linearity appeared a bit better on the scope when adjusted to the rated 5W level, then pad it externally, if desired. Knock-on-wood, its been reliable so far.

It took awhile to get mine as the Greek supplier builds them when he feels like it, apparently, though maybe the situation has improved by now. Phil at T'R'us is a good guy to deal with.
 
> Hi. Is anyone familiar with the RPG 20 Low Power AM
> Transmitter by TransmittersRUs.com
>
> http://www.transmittersrus.com/tru_rpg20.htm
>
> Supposedly it is adjustable from 100mW to 20W
>
> This would be great for a campus station perhaps, but how
> well does it perform? Is it a winner? or is it going to
> blow right away?
>
> Thanks!
>
I guess one could ask the same question about a transmitter I saw that is adverstised as 4-10 watts but on a posting board they claim their unit can be brought down to the 100mw level. Here is the link if you would like to check it out. Scroll down to the bottom of the page.
 
Re: 4-10 watt AM tx

> >
> I guess one could ask the same question about a transmitter
> I saw that is adverstised as 4-10 watts but on a posting
> board they claim their unit can be brought down to the 100mw
> level. Here is the link if you would like to check it out.
> Scroll down to the bottom of the page.
>

I know the Site you are thinking of here. I have heard multiple negative things about their products. Several people had their 4-10 watt AM Transmitter arrive DOA (not working). Others had problems with FM TXs arriving DOA, or where they did arrive working blew after a few minutes. Someone else had an FM amp that worked for about 6 weeks and then failed. Apparently their best product is an FM Transmitter that fits into the PCI slot of a computer. That apparently lasts the longest, but will still fail after a finite amount of time. I bought their RDS encoder about a month ago, and it has never worked for me. The company will not send me or sell me a schematic.
 
> > Hi. Is anyone familiar with the RPG 20 Low Power AM
> > Transmitter by TransmittersRUs.com
> >
> I've been using one for a couple of years, works nice,
> sounds good too...

Wow, Thanks for the good deal of information.

Here is another question for you. I see that there is a meter on the front. What all does the meter read? Does it display modulation? or is it simply for output/reflected power?

Also, do you think it would work with one of Carl's antennas without any additional ATU?

I am looking to use a unit like this for a campus station like a regular part15 for now, and then when the paperwork goes through approving the property as an educational institution we can adjust it up to likely about a watt or so as a free radiate system. What makes this Transmitter so attractive is the easily adjustable power, and the adjustable frequency, unlike the other low power AM offerings from the domestic suppliers.
 
Re: RDS DOA

> I bought their RDS encoder about a
> month ago, and it has never worked for me. The company will
> not send me or sell me a schematic.

I too bought their RDS encoder, the RDS Max 3.0 over the summer and Still have not been able to get it to work. At first I thought because I was using it on an FM kit, but I tried it on two different Real FCC Certified exciters with SCA inputs and still nothing!

There is supposed tobe a new firmware upgrade coming soon, so I wil try that. If stil nothing i will try to send it back to them and hopefully they will fix it or replace it.
 
> > > Hi. Is anyone familiar with the RPG 20 Low Power AM
> > > Transmitter by TransmittersRUs.com
> > >
> > I've been using one for a couple of years, works nice,
> > sounds good too...
>
> Wow, Thanks for the good deal of information.
>
> Here is another question for you. I see that there is a
> meter on the front. What all does the meter read? Does it
> display modulation? or is it simply for output/reflected
> power?
>
> Also, do you think it would work with one of Carl's antennas
> without any additional ATU?
>
> I am looking to use a unit like this for a campus station
> like a regular part15 for now, and then when the paperwork
> goes through approving the property as an educational
> institution we can adjust it up to likely about a watt or so
> as a free radiate system. What makes this Transmitter so
> attractive is the easily adjustable power, and the
> adjustable frequency, unlike the other low power AM
> offerings from the domestic suppliers.
>


The Radio Systems TR-20 AM transmitter is your perfect choice, I have the 20 watt version, it is built like a tank, heavy duty construction, and if you unplug the amplifier section and use only the exciter, you can use anywhere from 100 milliwatts to 1 watt, it has an adjustable control for modulation and for RF power... the audio is excellent, I used mine for my high school radio program but had to stop using it in carrier current mode as the signal got bled into the audio/visual systems of the visual arts dept. and the additional filters I've tried did not help.

I am thinking of putting it up on Ebay but resist since these are hard to come by. Try Ebay or some other used transmitter resale sites, I've seen them with the ATU Coupler for around $600-800 (working condition)!

Radiopilot
 
> > > Hi. Is anyone familiar with the RPG 20 Low Power AM
> > > Transmitter by TransmittersRUs.com
> > >
> > I've been using one for a couple of years, works nice,
> > sounds good too...
>
> Wow, Thanks for the good deal of information.
>
> Here is another question for you. I see that there is a
> meter on the front. What all does the meter read? Does it
> display modulation? or is it simply for output/reflected
> power?
>
> Also, do you think it would work with one of Carl's antennas
> without any additional ATU?
>
>

The meter is switchable for FWD power & SWR, also a Calibrate position for correctly setting up the SWR reading at a given power setting. There is also an audio LED bargraph and modulation control knob.

Any antenna that will give it near 50 ohms resistive will work, since it is a typical 50 ohm SO239 output. Any antenna loading/tuning has to be a part of the antenna system.
 
Wow, Thanks for the additional info! This sounds like a great little transmitter.

> Any antenna that will give it near 50 ohms resistive will
> work, since it is a typical 50 ohm SO239 output. Any antenna
> loading/tuning has to be a part of the antenna system.

OH, So basically as long as the Carl style antenna is roughly 50 ohms it should work because it has the Tuning/Loading coil as part of the design?

Thanks.

HT
 
> The Radio Systems TR-20 AM transmitter is your perfect
> choice...and if you unplug the amplifier
> section and use only the exciter, you can use anywhere from
> 100 milliwatts to 1 watt, it has an adjustable control for
> modulation and for RF power... the audio is excellent.
>
> Radiopilot

Is the frequency user adjustable? or is it crystal set. If it is crystal, how difficult is it to change frequency?

This amplifier section, is this a totally separate part? Could you theoretically unplug the signal generator, and plug in an external rf source into the amplifier, for instance the composite output of a Harris AM Stereo Exciter?
 
> > The Radio Systems TR-20 AM transmitter is your perfect
> > choice...and if you unplug the amplifier
> > section and use only the exciter, you can use anywhere
> from
> > 100 milliwatts to 1 watt, it has an adjustable control for
>
> > modulation and for RF power... the audio is excellent.
> >
> > Radiopilot
>
> Is the frequency user adjustable? or is it crystal set. If
> it is crystal, how difficult is it to change frequency?
>
> This amplifier section, is this a totally separate part?
> Could you theoretically unplug the signal generator, and
> plug in an external rf source into the amplifier, for
> instance the composite output of a Harris AM Stereo Exciter?
>


The frequency is crystal set, meaning you must remove the crystal and add a new one to change the frequency, but must be done such that frequencies above 1100khz thru 1710, 5 capacitors and 2 inductors must be changed along with the crystal of choice for the frequency if the unit was low band (510-1099khz)... The unit when I bought it was for 1290khz but I needed 1550khz so it was an easy crystal change (unit was high band)... Crystals are obtainable from Radio Systems for $35.00...

The excitor and amplifier are separate boards and you can unplug the amplifier and use another amplifier in it's place as the excitor outputs 1 watt max. or as you say you can plug in the Harris excitor but not sure if you have to tweek the excitor to insure you don't over saturate the first stage of the amplifier and ruin the rf transistors... they easily will cost you $125.00 to replace them.

Try Radio Systems website for tech notes...

http://www.radiosystems.com/Technotes/tr-xxxx.html

Worth a try...

Radiopilot
 
> > > The Radio Systems TR-20 AM transmitter is your perfect
> > > choice...and if you unplug the amplifier
> > > section and use only the exciter, you can use anywhere
> > from
> > > 100 milliwatts to 1 watt, it has an adjustable control
> for
> >
> > > modulation and for RF power... the audio is excellent.
> > >
> > > Radiopilot
> >
> > Is the frequency user adjustable? or is it crystal set.
> If
> > it is crystal, how difficult is it to change frequency?
> >
> > This amplifier section, is this a totally separate part?
> > Could you theoretically unplug the signal generator, and
> > plug in an external rf source into the amplifier, for
> > instance the composite output of a Harris AM Stereo
> Exciter?
> >
>
>
> The frequency is crystal set, meaning you must remove the
> crystal and add a new one to change the frequency, but must
> be done such that frequencies above 1100khz thru 1710, 5
> capacitors and 2 inductors must be changed along with the
> crystal of choice for the frequency if the unit was low band
> (510-1099khz)... The unit when I bought it was for 1290khz
> but I needed 1550khz so it was an easy crystal change (unit
> was high band)... Crystals are obtainable from Radio Systems
> for $35.00...
>
> The excitor and amplifier are separate boards and you can
> unplug the amplifier and use another amplifier in it's place
> as the excitor outputs 1 watt max. or as you say you can
> plug in the Harris excitor but not sure if you have to tweek
> the excitor to insure you don't over saturate the first
> stage of the amplifier and ruin the rf transistors... they
> easily will cost you $125.00 to replace them.
>
> Try Radio Systems website for tech notes...
>
> http://www.radiosystems.com/Technotes/tr-xxxx.html
>
> Worth a try...
>
> Radiopilot
>


Forgot to mention that this unit can be syncronized to other TR-20 transmitters, one unit being the slave and as many remotes as needed. See the Radio Systems website for details on how it's done.

Radiopilot
 
Thank you for all of the information. I find on Radio System website that they no longer make the TR-20, but now make a TR-6000 which is able to create more output power (Which is not of great importance for my pourpose) And even better it is able to be PLL Tuned, with the manual showing how to set the switches. That makes this a transmitter that allows the user to easily change to a new channel if the need arises. It is also rack mountainable. It will participate in a sink system as well. It has a jumper for using it with a TIS rig.

Thank you again for giving nice good advice.

HT
 
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