I just got a catalog and in it there is a dual band amp for boosting an HT's power. Does any body know if such a device is worth buying? Thanks

Jim, thanks again for the useful information!

Shannon

Jim,

I was wondering if I could solicit your help once more. I have a radio control transmitter that I would like to increase the power out put on. The schematic is at the following URL:

http://www.linearfusion.com/images/tx_schem.jpg

If you have time and don't mind this kind of thing, do you see a quick trick to increased power output?

Thanks, Shannon

Jim,

Yes, the fan is actually a CPU fan plus heatsink out of an old 200Mhz computer. The power transistor sets into a hole in the heatsink. The amp has holes drilled in the bottom of the enclosure just below the CPU fan. Seems to work well, however I may be hearing a "slight" noise from the fan... further testing will tell.

Well, thanks again for all of the help... I see that there is a link to a "HF" amplifier project to the left of this message board under "TekTalk". I am studying for my General ticket (written and morse) so who knows whats next!

Take care, Shannon

Great - looks good!
I see you have a fan to force some air. Do you have some sort of heatsink on the transistor? You need something to conduct the heat away.

Jim

OK Jim, I finally got some pictures up on the web!

See the following link:
http://www.linearfusion.com/kg4geh/fara.htm

The pics are kinda big....
73's KG4GEH

Your output should not be lower without the attenuator. Have you checked the calibration of your wattmeter? How much drive does the HT measure on the meter? Can you check the SWR between the HT and the amplifier. It could be a bad cable or piece of RG-174 internal to the amplifier. Currents look normal, recheck the output tuning.

Jim

Jim,

I took your suggestion and went back and tightened up the solder joints and shortened leads, etc. Had another ham, KE4LVT, make some recommendations on my coils (length,spacing) and went back through the tuning process. Same steps for KG4YXR.

One difference between the two amps is the fact that I do not have the attenuator in place on my amp... with 3.5 watts drive do you suspect this is why I am not seeing the same output?

Shannon

OK Shannon ... sounds great, send the pictures when your done.
With 3.5 watts drive you could change the attenuator to a -2dB
pad which would increase the drive and the output a tad. What did you do to get the power up?

Jim

Jim,

Alright! I think we are in business. Between two amps, we are seeing the following results.

KG4GEH(Mine) = 21 Watts
KG4YXR = 25 Watts

Both at about 3.5 to 3.6 Amps. Actual power from the HT's is closer to 3.5 Watts.

Thanks again for your help, pictures are on their way (as soon as the amps are dressed up real nice, labels, flame tested, etc...)

Take care, Shannon

Jim,

Quick correction/update... After looking at my watt meter again, I realized that I was only getting about 8 watts, not the 10-12 I mentioned earlier. So I took the attenuator out of line and got an immediate 2watt increase in power... now I have a full 10 watts (a double in output, hey, that's something!) with roughly 4 1/2 watts coming from my HT.

Thought I would pass that on... I'm still hackin' away.

Thanks, Shannon

Jim,

Thanks for posting a reply so quick!
Good news then on C5 and C17, the relay seems to be working just fine. I do have the RF attenuator in place with the foils cut. My HT is a Yaesu VX-5R and according to my watt meter, it looks like I am sending about 4.5 watts to the amp. I have a 12V (13.6 or there about) power supply rated at 25 Amps. I did take the time to solder all 18 of the holes through the board with the z-wires.

I think my plan of attack is to go back and "dress-up" my solder joints and try re-tuning from there. One thing I better mention right now is the fact that I am using a CPU fan w/heatsink to cool my power transistor... it pulls about .06 Amps, but I may take it out of the loop and see if that improves the performance.

Thanks again for offering help via. telephone... even when this thing is done I may give you a shout just for a verbal thanks.

Take care, Shannon

Well ... that's not a bad start. C5 is OK with a .1 or a .01 it's just a bypass. C17 is for the RF activated relay, .1 is
desired. If the relay pulls in with RF your OK. These won't
have any effect on the output power.
Regarding power output...
Is the RF attenuator in place with the foil run cut?
How much drive power do you have from your HT?
What is the voltage and current rating of your power supply?
How do the capacitors tune? I seem to recall one of the
output caps being fairly tight (max). Tighten one and peak
the other then alternate back and forth (pause in between)
tuning for max power out.
Are all of the through holes on the board pinned and
soldered well? How about the emitter joints?
Whenever one of the amps here had a problem my first action
was to resolder the connections.
Good Luck - If your still unable to get the power up send me your telephone number at WA1GPO@arrl.net or give me a call. I'm OK in the 'callbook' and telephone directory.

Jim

Jim,

Well, the amp project is complete. With the help of another ham, KG4YXR we fired it up today. The good news: No smoke! The not as good news: I am only able to get about 10-12 watts out of the amp after tweaking the Arco's. One thing we noticed was C5 and C17 are not .1uF, the part that came from Mouser ended up being a .01uF! Do you think this could be the problem... the closest thing we have found for a replacement has been some Caps from Radio Shack, but they are not 500WVDC, they are 50WVDC, but they do have the right capacitance rating (.1uF). Is this a good place to start? As soon as I am comfortable with the tuning I am going to post some pics to a website.

The project has been lots of fun, and I can't say thanks enough for the advise.

Take care, have a good weekend, KG4GEH

Sorry ... didn't specify a switch.
It's a DPDT toggle switch with both poles in parallel
to increase the current rating. Try a Radio Shack
275-663 or a Mouser 506-MTA206N. Only the + lead
is switched.

Jim

Jim,

Concerning the switch... do you have a part #... plus I am having a hard time understanding why both + and - are connected???

Thanks, S

I don't remember if C3 is polarized ...

Jim

Jim, I promise this will be the last question for awhile... but are all of the capacitors used "non-polar"???

Thanks, Shannon

Jim, great... I finally have have all of the pieces "in" now... I will post a web site link soon for the progress!

KG4GEH

Yes ... non-tinned will work.
Jim

Jim, would it work if I used non-tinned 18 guage copper wire??

Thanks, Shannon

Jim,

Thanks again, I believe I should be able to find some, but if not, thanks for the "fall back" plan!

Take care, Shannon

Nothing special #18 Buss wire. If you can't locate any,
drop me your address at WA1GPO@arrl.net and I'll send
you some.

Jim

Jim, I have orded all of the parts, should be here in a couple of weeks. Would you mind helping me out with the #18 wire for the coils??? Is this just 18 guage copper wire, or something more specific?

Thanks again, Shannon

Contact FAR Circuits for amplifier (reference 73-Nov.93)
PC board.
Jim

FAR CIRCUITS
Printed Circuit Boards
18N640 Field Court
Dundee, Illinois 60118
(847) 836-9148 Voice/Fax

email: farcir@ais.net
Note: Do NOT order via email; see order info

Jim, thanks again for all of your help... I will post a link to my (2m) completed project which I am expecting to start really soon!

As for the dual-band, wish me luck ;o)

73's KG4GEH

Answers to previous post ...

1. 6&2 meters will pass fine. I expect that it would be OK
on 70 cm - depends on the relay inductance. You might try adding and tuning the relay series cap (C15 -ARCO404)for the lowest SWR on 440 and live with what you get on 2M. It will probably be OK (I haven't tried this ... let me know).

2. The output network is VHF only ... you get to design the dual-band version!

Jim

I have a couple of questions concerning this project, thanks ahead of time for the information!

1. If you have a HT with a single output (6m, 2m, 70cm), to a dual or tri-band antenna. What happens when those signals pass through the amplifier? Will I need a duplexer/triplexer with multiple antennas?

2. Could this project be easily duplicated for UHF or a dual band amplifier?

Shannon, KG4GEH

The parts list may be found at:
http://www.falara.org/tektalk/2mampparts.html
(paste into browser). There are also links to it from the main article
http://www.falara.org/tektalk/GPOAmp.html

Edited by author 02-20-2003 09:28 AM
Hi,
Welcome to the FARA 2 meter amplifier FAQ pages.
If an individual response is requested please forward
a copy of your message to WA1GPO@ARRL.NET.
73's
Jim