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Author Topic: amp for IC-705  (Read 1074 times)

KD2HPQ

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amp for IC-705
« on: July 26, 2021, 07:22:01 AM »

The reality of qrp phone operation becomes apparent during poor propagation. The IC-705's lovely spectrum scope helps you find signals but not reach them. I am therefore looking for an amplifier I can take in the field to boost my IC-705 to the 30-40w level. Any suggestions? I need something that is plug and play. I have never used an amp.
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K0UA

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Re: amp for IC-705
« Reply #1 on: July 26, 2021, 08:23:11 AM »

Maybe this little chinese amp.
Here is a video

https://www.youtube.com/watch?v=3eafDcy9fyc
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73  James K0UA

G4AON

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Re: amp for IC-705
« Reply #2 on: July 27, 2021, 12:44:04 AM »

I use a Hardrock 50 with my Elecraft KX3, it only has HF/6, if that will suffice.

This page is a good write up: https://ae5x.blogspot.com/2018/12/thoughts-on-hardrock-50.html

The Hardrock 50 should be shown on this page, but currently it doesn't appear to load:
https://www.hobbypcb.com/

73 Dave
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KU3X

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Re: amp for IC-705
« Reply #3 on: July 27, 2021, 05:48:23 AM »

Rather than invest in just more gear to carry around when setting up portable, why not get an IC7300 new or used. Even an FT891 is a low priced HF radio very popular with the hams that set up for Parks on the Air. The Elecraft 100 watt solid state amp is more expensive than an IC7300. The Hardrock amp is neat but you are going to assemble it. Watch out for some of the junk sold on Ebay. A lot of the cheap ones don't have band pass filters with them and that's needed to use on HF. Xiegu made an XPA125 amp. That model amp does not pass FCC specs. They later came out with a "B" version. That one does pass FCC specs. Getting back to Chinese ebay amps......just because some do have band pass filtering, "Do they pass FCC standards?"
I set up QRP portable and 99.9% of the time I use 5 watts CW. If I want 50 watts or more, I take my FT991A.
Barry, KU3X/QRP

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KD2HPQ

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Re: amp for IC-705
« Reply #4 on: July 27, 2021, 06:22:37 AM »

Rather than invest in just more gear to carry around when setting up portable, why not get an IC7300 new or used. Even an FT891 is a low priced HF radio very popular with the hams that set up for Parks on the Air. ...
Barry, KU3X/QRP

Barry, you and I think alike. See my next post.
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KD2HPQ

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Re: amp for IC-705
« Reply #5 on: July 27, 2021, 06:24:16 AM »

Thanks to all who responded. I am a relatively new ham and always get a nice education when I post here.

There appear to be three solutions to this problem:

1. Develop the amazing operating skills of the Youtube ninjas, whose 5w CQs are always answered, often resulting in a pileup
2. Spend almost as much as my radio cost to get a suitable amp and have another bag of crap to drag along, more batteries, and yet another set of wires dangling like spaghetti
3. Buy a used HF 100w radio as my "outdoors" radio

Number 1 is fantasy outside of band openings. #2 is out of the question, not because of the $$$ but I already carry way too much crap when I'm portable. #3 is the only sensible option, IMO. One radio, one battery, one antenna.

Too bad I just sold my IC-7100.
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KB1GMX

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Re: amp for IC-705
« Reply #6 on: July 27, 2021, 09:21:11 AM »

You left out item 4...

4. Use a good full size antenna at decent height.

Loaded whips are inefficient, may have poor grounding so good SWR
is not always best signal.

Dipole or half wave end fed wires are efficient and the monoband ones
are about as effective as any field antenna possible short of beams (wire or aluminum).

Most of the time its about site and antenna.  Being on a high spot or mountain helps.
Using the best antenna possible backs that up.

Frm home use a beam.  Easy one is the VE7Ca triband (20/15/10)
wire beam. We have used that for FD a few times and its not to
bad to set up and works well.  Another time a TH3jr at 30ft
proved to be very good.

An amplifier can make up for a crappy antenna, sometimes.
Also operating on a band that is poor for various reasons is
an exercise in frustration.  Generally in the field 40 or 20M
is the most often winner and if 15 is open it can work well,
but it has to be open.

In the end I have FT817 for portable and fun, TT Eagle 100W
for the home, FT440S/AT mobile (semi-portable 100W).

Why, because none can be optimal for everything.

Allison
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K0UA

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Re: amp for IC-705
« Reply #7 on: July 27, 2021, 10:24:03 AM »

Thanks to all who responded. I am a relatively new ham and always get a nice education when I post here.

There appear to be three solutions to this problem:

1. Develop the amazing operating skills of the Youtube ninjas, whose 5w CQs are always answered, often resulting in a pileup
2. Spend almost as much as my radio cost to get a suitable amp and have another bag of crap to drag along, more batteries, and yet another set of wires dangling like spaghetti
3. Buy a used HF 100w radio as my "outdoors" radio

Number 1 is fantasy outside of band openings. #2 is out of the question, not because of the $$$ but I already carry way too much crap when I'm portable. #3 is the only sensible option, IMO. One radio, one battery, one antenna.

Too bad I just sold my IC-7100.

Tell you what. If you like, I will swap you a Icom Ic-7300 even up for your Ic-705 .  As you know the 7300 is a hundred watt, all day every day rig that can be dialed back to around 1 watt if need be.  160 meters thru 6 meters. All mode. Contact me and we can talk about it.
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73  James K0UA

KD2HPQ

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Re: amp for IC-705
« Reply #8 on: July 27, 2021, 10:31:09 AM »

Thanks for the offer but I already have a 7300, and it lacks vhf/uhf. If I get anything else it will be a 991a, but first I have to see its current draw at 20, 30, 40w, etc. Do you know if these numbers are more or less linear, e.g. drawing 20A @ 100w, 10A @ 50w, 5A @ 25w?? Even 5A will require an expensive additional battery but it is do-able. 15-20 A is not.
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K0UA

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Re: amp for IC-705
« Reply #9 on: July 27, 2021, 10:46:18 AM »

Thanks for the offer but I already have a 7300, and it lacks vhf/uhf. If I get anything else it will be a 991a, but first I have to see its current draw at 20, 30, 40w, etc. Do you know if these numbers are more or less linear, e.g. drawing 20A @ 100w, 10A @ 50w, 5A @ 25w?? Even 5A will require an expensive additional battery but it is do-able. 15-20 A is not.

While I don't have the figures readily at hand, I can tell you the current draw is NOT linear. For instance most 100 watt rigs will draw close to 3 or 4 amps with NO power output. This is the bias current for the finals. You can perform the experiment with you existing 7300 and the results will likely be close to what the 991A will do also. Example if the rig draws 20 amps on peak at 100 watts, the current draw at 50 watts WILL NOT be 10 amps. It will likely be closer to 15 amps. There is some savings by reducing power to 50 watts or even 25, BUT it is not going to be 1/2 or 1/4. Sorry to be the bearer of bad news.
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73  James K0UA

K0UA

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Re: amp for IC-705
« Reply #10 on: July 27, 2021, 10:55:46 AM »

I did a quick and dirty test with my 7300 by sending a carrier and measuring the drain current of the finals using the 7300's own Id current meter on the 40 meter band into a dummy load.

Watts     Amps of drain current

100        18
 50         14
 25         12
 10          8
   5          6

Now keep in mind this is JUST the drain current of the Mosfet finals. there will be maybe as much as 2 amps drawn for the rest of the exciter stages of the radio, so add about 2 amp for each of the above readings and that will get you in the ballpark.  I suspect the 991a will have similar results.
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73  James K0UA

K0UA

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Re: amp for IC-705
« Reply #11 on: July 27, 2021, 11:06:05 AM »

As you can see a 100 watt rig when turned down is not a very efficient QRP rig. None of them are, These rigs are not optimized for low current operation and the bias current is a major stumbling block. The bias current on most 5 watt maximum rigs is measured in milliamps not amps. Also the receivers are optimized for low current drain. Bottom line is that QRP rigs are designed for low current operation and 100 watt rigs are not.  That being said, all it takes to operate these 100 watt rigs in portable field op's is just a sufficient battery for the length of time you want to operate.  LiFePo4 batteries are your friend in the weight to power equation.
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73  James K0UA

KD2HPQ

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Re: amp for IC-705
« Reply #12 on: July 27, 2021, 11:09:24 AM »

K0UA: You are quite the Elmo :)

I suspected as much. @ 25w a drain of 14A means too much battery to lug around.

I'm going to look into an efficient, resonant antennas for 40-20 and whatever else is possible. But even that is a lot of wire. One of the cruelest statements ever made by a ham is, "just throw a wire into a tree." At 5 or 10w it had better be a very high-performing wire indeed.

I will ping you with questions! Thank you.



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G4AON

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Re: amp for IC-705
« Reply #13 on: July 27, 2021, 11:13:23 AM »

These are the measured power levels and current for my TS-480sat, 12.4V from a bench supply, CW key down, band 6m. Power meter LP100.

Power level (as set)   Power output   Current   
100W         88W   16.5A   
75W           75W   15A   
50W           52W   12.5A   
25W           26W   9.2A   
10W           11W   7A   
RX current   1A, Varies slightly with backlight levels and volume

As others mentioned, reducing power doesn’t give a linear drop in current drawn. Note, the radio cannot produce 100W from 12.4 Volts.

Many of us have a selection of radios for various purposes. Decide on the job you want the radio to accomplish, it is a tool to help you communicate. Sadly, many buy a radio as a bench ornament.

73 Dave
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K0UA

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Re: amp for IC-705
« Reply #14 on: July 27, 2021, 11:33:01 AM »

K0UA: You are quite the Elmo :)

I suspected as much. @ 25w a drain of 14A means too much battery to lug around.

I'm going to look into an efficient, resonant antennas for 40-20 and whatever else is possible. But even that is a lot of wire. One of the cruelest statements ever made by a ham is, "just throw a wire into a tree." At 5 or 10w it had better be a very high-performing wire indeed.

I will ping you with questions! Thank you.

Ok, a good efficient antenna is always a good plan at any power level. My "quick and dirty" method of current measurement is just a ballpark, as my method did not really take empirical measurements with a good current meter of the overall current needed, but it is close enough for you to get the idea across that the current draws are not in a linear fashion.

 Also don't forget that band conditions play heavily into how much power is needed to make a good contact. And that also our upper bands will only get better as the cycle 25 develops into whatever it will do. The upper bands typically need less power for good signals to be propagated.
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73  James K0UA
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