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On Sat, Jul 13, 2024 at 06:53 AM, ajparent1/kb1gmx wrote:

So the QRPL amp with the HL2 17dBm output is a better match to the task.
If that ends up being too much drive a small low power (50mW) 2-4db
attenuation is far easier to do if needed.

Hi Allison

I rigged up a 50ohm BNC dummy load and connected it to the DSO, (Siglent SDS1102CML+ 100MHz Dual channel oscilloscope), and life is suddenly V good, see table below !!!

Fmeasure=	5398.5	KHz	Zload=	50	ohm
?	?	?	?	?	?
dB Output	Vpp	Vrms(mV)	V^2	P(mW)	P(dBm)
-7.5	1.77	580	0.3364	6.73	8.28
-7.0	1.80	620	0.3844	7.69	8.86
-6.5	1.90	660	0.4356	8.71	9.40
-6.0	2.00	700	0.4900	9.80	9.91
-5.5	2.10	740	0.5476	10.95	10.39
-5.0	2.24	780	0.6084	12.17	10.85
-4.5	2.36	820	0.6724	13.45	11.29
-4.0	2.52	880	0.7744	15.49	11.90
-3.5	2.66	920	0.8464	16.93	12.29
-3.0	2.80	980	0.9604	19.21	12.83
-2.5	2.96	1040	1.0816	21.63	13.35
-2.0	3.16	1160	1.3456	26.91	14.30
-1.5	3.36	1180	1.3924	27.85	14.45
-1.0	3.54	1280	1.6384	32.77	15.15
-0.5	3.76	1320	1.7424	34.85	15.42
0.0	4.00	1400	1.9600	39.20	15.93

So the RF1 17dBm output is indeed fully variable, and a simple fixed 3dB attenuator between it and the QRPLabs 10W PA should bring down the drive level to around 25mW.

The "dB Output" data are the values from the "Drive Control" in the Thetis SDR s/w, ie 0dB is full power out

Thank you ever so much for your suggestions, and prompting me to try the 17dBm output, this certainly makes for a cleaner/simpler design both philosophically and practically.

Thank You once again, 73

Peter - GM8JCF

Hi

I've redrawn the system schematic to reflect using the HL2 0~17dBm RF output, please see below




And in case the quality is insufficient, there is also a .PDF attached.

Could I please ask that you all take a close look and find errors, suggest improvemnts.

I would really like to thank everyone for their ideas, and suggestions in helping me to get this right, but special mention must go to KB1GMX, thank you Allison.

Than You, Take Care All, 73

Peter - GM8JCF

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
------------------
Post online only,?
direct email will go to a bit bucket.

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

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

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.

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.




--
?

73, Barb

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

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 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

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
------------------
Post online only,?
direct email will go to a bit bucket.

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