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2m Filters + random nonsense

Hi folks

We have had some prototype miniature helical filters manufactured for us. Ideal for reducing breakthrough perhaps? Two and three cavity versions.

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If the price is okay’ish :smile:
Yes, please for our club APRS Igate.

73, Joe

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From my experience, in a superhet receiver, filters like this are traditionally fitted after the RF amp to provide adequate image rejection. Fitted prior to the RF amp, I would have thought that they would only be of use as breakthrough filters in circumstances where 2.8 dB insertion loss could be tolerated such as in a point- to-point link. If we must reduce breakthrough by installing RF filters, multi-element cavity filters are the only real contender but perhaps not on most Sotas?

Regards
David G0EVV

I don’t know how these perform but it sets a price tag, I guess there will be an extra 20% VAT plus £8 to the Post Office after BREXIT. So UK filters may be more desirable.

https://www.antennas-amplifiers.com/2-meter-bandpass-filter-transmitting-50w

I must admit I have had more problems with the 4m band and Rx overloading from nearby TV transmitters. But to present I have not found the desire to carry more kit to the summit.

73 de Andrew G4VFL

Here is a photo of a filter: SMA for scale. They have been designed to put in front of a handy to stop blocking from comms sites, also could be handy for satellite operations.

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Votes on the worst site for 2m breakthrough problems in North West England/N Wales. I need to test a filter!

  • Billinge Hill
  • Gt Orme
  • Cloud
  • Winter Hill
  • Cyrn-y-Brain

0 voters

My current Yaesu FT-70D is, by far, the best HT I’ve ever had in respect of rejecting unwanted rubbish. In fact it’s the best HT I’ve ever had full stop.

Out of your five nominations, only one location even hints at causing problems on the FT-70D - Great Orme. Of the other four, Winter Hill and Billinge Hill used to be problematic on previous handhelds. QRM has occasionally been detected when on Cloud or Cyrn-y-Brain, but only rarely in my own experience.

It made me reflect on just how good the FT-70D is - unless things have dramatically improved on G/SP-010 and G/SP-017!

Day out to Llandudno for you Richard… If you’re going for a wander up Tal y Fan as well, I might invite myself to come along…

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Hi Richard

Not had any issues on any of your listed summits with an FT-60, FT-290 or FT-817. Only summit I’ve had a real problem on (with the FT-290) was Dundry Down G/SC-010 but that’s a bit off your patch and it was back in 2007. Must have been bad because I remember the struggle to get contacts clearly to this day :-s

Good luck with the filters,

73 de Paul G4MD

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Hi Richard
I have had problems over the years with the VX7R on Great Orme and to a lesser extent on Cyrn-y-Brain.
73
Nick

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It’s possible that things have indeed improved in some places as the paging network has largely been switched off and that used quite high power transmitters at round about 155 MHz. The problem with blocking is that it’s often hard to spot. I suspect that it happens more frequently than many of us realise.

Hi Richard

Breakthrough/de-sensing on my Yaesu FT2 a few weeks ago on Hope Mountain GW/NW-062. Had to change to my Yaesu FT270 which gave me 16 crystal clear chasers in my log. The Summit/Trig is above Communication towers

Any progress on creating a DIY kit for those filters you have sourced?..probably what you want to test now :grin:

73 Allan

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A little off the target area, but The Wrekin G/WB-010 has caused me blocking / de-sensing (as distinct from audible interference) on 2m - to the VX5 in all circumstances, and the Wouxun KG-UV6 (generally very good) only when used with my wire Jpole antenna.

Yes, I’m sure you are right, especially when a more efficient antenna is connected.
If the filter allows the use of a decent antenna a few metres above ground, then in many cases the improved performance should outweigh the 2.8dB insertion loss by a significant margin.

It’ll be interesting to see some results.

73
Adrian

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Hope Mountain and Dundry Down are two more that seem much improved - but is it the quality of my reasonably new FT70D or the lack of pager QRM? Point taken about blocking hard to spot. Making plenty of contacts at a fast rate with a HT on all these summits in recent times suggests it’s not causing a problem, but it can’t be ruled out!

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Brown Clee can be bad too!

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Yeah, Brown Clee is one like Great Orme where the QRM is still very noticeable. Rarely have I had issues on The Wrekin.

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You could almost throw a stone to 4 amateurs from The Wrekin (please don’t try this at home boys and girls) and I have rarely heard any interference.
It is a nice steep sided summit out in the clear, so should have excellent take-off for longer distance QSOs too.
For filter testing, I guess you could to listen for beacons, or distant repeaters maybe, with / without the filter?

Brown Clee is very noisy, FT817 territory :o)

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I must be missing something here. I can understand the need for filters on receive, but what do you do on transmit?
With a 5W handheld nearl 2 1/2W will be lost either in the filter or reflected back into the Tx.
SMAs are too fiddly to connect and reconnect after each over. A bypass facility with relays adds complexity but could be operated as an RF VOX, particularly on FM. PIN diodes?

John
G4YTJ

Hi John

The simple answer is that you leave the filter in circuit. The small loss on TX is greatly outweighed by the advantages of being able to hear callers. A few of us built filters some years ago. These had nearly 6dB loss but they were very effective for SOTA.

Bypassing the filter is possible of course but would add to costs, complexity, size and weight.

Hi Richard,

I activated Cyrn-y-Brain in March this year, using a
Yaesu FT-270 and vertical dipole 4m above ground.

I sat right behind the big tower for best shelter, and
the FT-270 meter showed S4 of noise with no filter.

This vanished when I added a DCI-145-2H in circuit.

The DCI is fantastic, but it’s very big and heavy!

Sadly I don’t get out enough to experiment much,
but would be interested in something smaller and
lighter even with somewhat lesser performance…
I like Allan’s suggestion of supplying a complete kit.

73, John M0VCM

I think this is a very useful product. Many previously respected brands of HT radios as well as recent economy brands virtually collapse in the presence of high level broadcast and other signals. It isn’t a question of whether the user “hears” interference such as audio from broadcasting or other services, buzzing sounds or anything else. The user is nearly always unaware that unwanted signals are reducing the performance of their receivers.

The problem can be identified as an activation where the user calls many cqs without any replies. They later are told there were many replies which they did not hear.

The selectivity of the front end of most of these radios is almost nonexistent. Adding a filter to cut down the unwanted signals usually has a miraculous effect.

I hope this product line is very successful.

It would not worry me to lose a few db on transmit if it meant a big improvement in receiving performance.

73 Andrew VK1DA/VK2UH

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