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On Sun, Jul 14, 2024 at 08:50 AM, ajparent1/kb1gmx wrote:

I make it a point of using separate relays to get better isolation and often its
a mechanical convenience as well.

Thank you for that very practical tip, given how low cost these little relays are, it's probably best to carry out that seperation as you suggest - I;ve never built an RF amplifier before, so all these tips are most helpful

Thank you, 73

Peter - GM8JCf

One area is that input and output must not be close as in using the same relay.
If isolation is not enough oscillation can be a unwanted result.
I make it a point of using separate relays to get better isolation and often its
a mechanical convenience as well.


--
Allison
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On Sun, Jul 14, 2024 at 07:20 AM, Timothy Fidler wrote:

Put colour coding via Red and blue heat shrink on the Two cables which have the common BNC connectors and a red and blue spot adjacent to the bulkhead connector at the amp. Viz J2 and J5.

Useful tip, thank you

Peter - GM8JCF

On Sun, Jul 14, 2024 at 07:20 AM, Timothy Fidler wrote:

Use a contact from Relay one ?as a the input controller for the RF use a contact from Relay 2 as the output controller for RF out. ?Currently you have RF in and RF out in the same relay. Some ?Chinese boards do that (RF in and RF out in the same relay housing ) but it is not good practice.

?

Tnx for the tip

Peter - GM8JCF

On Sun, Jul 14, 2024 at 08:22 AM, Barbaros WB2CBA wrote:

Here is my take of QRPL linear 10W PA which I use with my usdx trx. I thought this might be a helpful guide for you.

Hi Barb

Thank you very much indeed, really detailed instructions, very much appreciated.

73

Peter - GM8JCF

Hi Peter,

Here is my take of QRPL linear 10W PA which I use with my usdx trx. I thought this might be a helpful guide for you.




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?

73, Barb

my back of envelope calcs show that if you use four pole filters and chose the correct break point for the 5 Mhz filter at about 8.5 Mhz you can put in a no switched filter set for 60- 40- 30 mtrs and get about -17 dB suppression for all of those three bands The basic LP filter design for the 7 Mhz filer would be as per the Qmx 40/30 mtr filter. However if you had only 2 poles for the 7 Mhz filter you'd get only about -13 dB of suppression on the 14 Mhz harmonic which may be/ would be light on once the primary signal had gone up to 55.4 dBm

his concept is on the basis that 60-40-30-20-17-15 MTRS is a complete band set that is acceptable . Spinning the cat by the tail that way may make it possible to have only one set of DPDT Relays (a pair) providing filter selection over that entire range. This the post 10 W amp filter I refer to. THis is based on harmonic plots I have seen published for the bare Hermes Lite.

Hey guys,

I just finished building my QMX a week ago and bought a dummy load to do some testing. when connecting the dummy load to the QMX was getting a SWR on most bands (10+ at the highest and 3.3 at the lowest). I then connected an SWR meter in series with the dummy load and it told me a different story. Here are the readings by band:

Band QMX SWR Reading Standalone SWR Reading
80M 10 1.82
60M 7.3 1.18
40M 8.2 1.01
30M 10 1.01
20M 3.3 1.01


I tried to research this issue a little bit, but I couldn't really find any answers. Some SWR issues seem to be fixed by rewinding the T507 SWR bridge. Any help would be greatly appreciated.

Use a contact from Relay one ?as a the input controller for the RF use a contact from Relay 2 as the output controller for RF out. ?Currently you have RF in and RF out in the same relay. Some ?Chinese boards do that (RF in and RF out in the same relay housing ) but it is not good practice. ?Some will burst into oscillation as result ?I'm sure.

?

Detailed build item -
Put colour coding via Red and blue heat shrink on the Two cables which have the common BNC connectors and a red and blue spot adjacent to the bulkhead connector at the amp. Viz J2 and J5.

TEF

In the message menu are interval and repeat set to zero?

On Sun, Jul 14, 2024 at 05:36 AM, ajparent1/kb1gmx wrote:

One note if you go direct to antenna (not using the BLA-amp) from the
QRPL amp a set of low pass filters are needed.

Thank U Allison, it is tempting to add a set of the QRP Labs low pass filters so as to make a fully standalone 10W Linear Amp; something to think about indeed.

Once again, thank you

Peter - GM8JCF

Q202 and Q201 are the bias regulator for the drivers Q203 and Q204.

Q206 is for Transmit enable (enables bias to the amplifier transistors).


--
Allison
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A bad pot could be the case. Especially true if one varies differently than the other.

I've not found the bias to be "jumpy" or all that sensitive in adjustment for mine
(N=5). The bias does increase with heating but not enough to be a problem.

I assume you have a dummy load at the output and input.

Note Q206/7 are the IRF510 finals. The BS170 bias is independent of the
final bias but share common 12 switching.

--
Allison
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That should do what you desire.

One note if you go direct to antenna (not using the BLA-amp) from the
QRPL amp a set of low pass filters are needed. Driving the amp that
is not required.

--
Allison
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George- Thanks for your suggestion. I did delete the entire message #2, then replayed it, but the issue remains even after cycling the rig.
————————-
Jim?
N7RCS
Palm Bay, FL

Hi Steve,

thanks for the input. I've checked the desoldered IC, the several supply to ground resistances showing normal values in the kOkm range.
I should get my replacement PCM1804 end of next week, I hope it will solve the issue.

And 24 hours later, it's still standing. So this tape can handle it and is approved for this usage :-)

The 3D design of this tilt feet can be accessed through (just click on the 3D picture).

--

73 Lex PH2LB?

The circuit includes the third BS170 in a clever voltage regulator circuit loop so that the supplied bias voltage tracks the BS170’s gate threshold change with temperature

You should be seeing around 120mA going through the drivers with /TX grounded but the PA bias pots anticlockwise

Yes the PA pot adjustment is very sensitive - a fixed resistor in series would have helped but as you’ll note PA bias immediately varies with warm up anyway so get it in the right region and be happy

On 14/07/2024 07:02, Alan G4ZFQ via groups.io wrote:

Finally found this

Not finally, I now remember where I wrote the full story