New project on www.sm0vpo.com - Basic HF / VHF filters

condolences

Oh...  What to say?

Accept my deep sympathy and be strong.

Thinking about you, Ivan

That is very bad news. My condolences.
I read yesterday how you hoped to be able to spend the summer together.
Even early this morning I visited the forum, hoping to read some positve developments.
Life can be cruel...
I wish you all the strength in this difficult period.

Ruud.

Hello Ivan and Ruud,

A little news, Maj-Lis passed away at 2AM this morning. I was with her until the end.
She was getting better on Saturday, but Yesterday she got worse in the evening.

Best regards from Harry - SM0VPO

Hi Harry,
I am glad to hear these good news. I pray for Maj-Lis to heal soon.

The method you used to design the filters is common. Nobody starts the calculation from scratch. When I used to design LC filters using a pocket calculator only, I started with a paper catalogue. It contained part values for a normal frequency (1 kHz?), loading (1 ohm), various approximations and degrees. I often used Chebycheff type with 1 dB ripple. My task was to re-calculate all part values for the required frequency and loading resistance.

VBR from Ivan

Hello Ruud and Ivan,
Maj-Lis is a lot better today. They are keeping her blood-pressure controlled low so the blood clot that formed is not leaking. But they are also keeping her on morphine for the pain. She cannot eat or drink anything- cannot keep it down. Today they moved her from ICU to a care-ward.

Yesterday the doctor asked for her near relatives to come to the ICU and told us that she cold die. She is a lot better today, but not "out of the woods". With her condition it could become worse at any time. The longer this lasts so the better are our chances of sharing another summer together. We just have to think positive and she needs to take it very easy.

Thank you both for your concern and kind words.

As regards the filter references, Ivan, perhaps you are right, there are so many references to standard designs on the WWW that it would not be relevant.

I took calculated values for 500MHz and the calculators only scale the values for any frequency. It made the java a lot more simple.

Best regards to you both from Harry - SM0VPO

Harry,
I am holding your hand in your trouble. Life brings very sad moments...

Re you article: IMHO there is no need of reference for filter design. Many books about LC filter design exist, from the maths and theory to catalogues of frequency normalized designs.

VBR from Ivan

I was touched by the last sentences in your previous post.
My thoughts are with you borh.

Hi Ivan,
Thank you very much, I shall correct the typos. Yes, the filter is designed for 50Ω.

I have been thinking about the calibration / adjustment and I think that the oscillator itself is VFO and covers up to 130MHz, so it could be possible to set the frequency to known values and make a slight adjustment. I gave really detailed info for the coils exactly as I wound them, including the pitch/spacing and it should be easy to duplicate.

I will also add references to the information upon which it was based. But it was RAF Locking (GC) engineering notes, QST 1978(? I think), and another link I cannot remember.

At the moment I have a few other problems. Maj-Lis was taken to hospital yesterday - blue-light job. Her aorta artery is ruptured and she is bleeding slowly into the chest. They cannot operate as they say she would not survive the operation, and the chance of success is very low. I fear that I may loose her.

Very best regards from Harry

Hi Harry,
you did a perfect job as always. Congrats!

Proper matching on both ends of any filter is essential. I suppose your designs are made for the usual 50 ohm resistance at both ends, but it should be written more clearly.

My experience is that Cauer class filters require fine tuning using a VNA (or a noise generator plus a spectrum analyzer, which do the same job) to get a really sharp rejection edge.

I found one small typo:"a 4.7pf and a 2.2pf in parallel to get 49.2pf" should be 47pF and 2.2pF, obviously.

VBR from Ivan

Hi all,
I have been working on a project that gave other "spin-off" projects. One of those is a stable VHF FM transmitter for 88-108MHz bands.

Ivan pointed out that I should include a decent filter because the FM band is VERY close to the aircraft band.
I know it is illegal in many countries, other countries turn a blind eye (if you operate sensibly), but in certain countries you could be carted away; never to be seen again.

But if you have your heart set on making a little FM transmitter then filtering is really important. In fact it is really important for ALL transmitting equipment, to prevent interference to other services.

Instead of just designing a filter, I documented three filters and even included a calculator to give the values. Probably a bit of overkill, but I had fun doing it. The filters I cover are:

1 - Basic Low-Pass (butterworth) for harmonic rejection
2 - Basic High-Pass (inverted Butterworth) for removing, for example, mixing products
3 - Elliptic filter (Cauer-Chebyshev) when you need a really sharp cutoff

I uploaded the files this evening. Have fun with them :-)

Very best regards - Harry - SM0VPO
(@Ivan - is this a good explanation of what you meant? The V8 TX will include a worked example on the PCB)