2 METRE INTERFERENCE | THE HIDDEN PROBLEM

[@bungle6668]

i love my SOTA beams bandpass filter, best £35 I ever spent on Portable equipment! Makes even my cheapest handie outperform my most expensive one! and many others with REALLY expensive ones too!

[@363505]

I'm so glad that you mentioned the lack of filtering in the front end of the portables RX. I've had a number of conversations with amateurs who believe that because they spent a lot of money on their rig that the problem must be with the hill top sites and not themselves. As soon as manufacturers brought out radios that tried to cover for example 130-180MHz with no front end tuning disaster loomed. A great video that not only showed the average amateur how to spot blocking but also some basic easy to try ways to reduce it. Many thanks for making the video, I feel that I maybe linking to it occasionally!

[@g3cwi_Radio_Adventures]

Thanks. You are most welcome!

[@victornelson1577]

Purchased one and using it for a year. I would not go up the hills without it now

[@joeblow8593]

The Radio Shack HTX-202 was probably one of the best 2 meter handhelds ever made because it was intermod resistant, it only picked up the 2 meter band and nothing else. Where other handhelds and scanners would have issues with intermod and paging signals in high density signal areas, the HTX-202 shined and worked flawlessly.

[@timb4655]

Thanks Richard for doing this. Excellent practical demonstration of an issue that probably affects more people than many realise, myself included

[@g3cwi_Radio_Adventures]

I think it's very common.

[@tech-rich]

Some good news is that Vodaphone have recently shut down their Pager network in the lower 164 MHz band. This was often a strong source of desense at many hilltops as the base stations were high powered.

[@REKlaus]

Thank you for the video. Explains the problems I have with my handhelds where I live, good receive on factory short antennas but poor receive on longer aftermarket antennas. This is the first time I have been able to get an answer that makes sense. Thanks again.

[@g3cwi_Radio_Adventures]

It's a more common problem than many suspect!

[@andrewd4890]

Great ideas for combatting interference to an HT. The best of them is the filter. Highly recommend that solution. Thanks Richard. (Vk1da)

[@g3cwi_Radio_Adventures]

Thanks - I did forget to include a directional antenna in the mix though!

[@andrewd4890]

Richard Newstead Well that would raise the interesting issue of what design of antenna to use, that will be directional across a wide range of frequencies. I guess the log periodic would qualify, but I don’t think they have enough off-boresight rejection, as on any given frequency they are really only as good as a 3 element yagi. At one site in Canberra I have had some success using horizontal polarisation instead of vertical (at both ends of the contact), but I don’t know whether that was successful due to increasing the signal strength on 2m or happening to reduce the level of local unwanted signal. Your demo of hearing the incoming 2m signal with the attenuation of an unconnected plug was perfect, showing that the receiver is fine until the high strength local qrm was fed into it. Beyond the scope of a demo is the question of what blocking is. As I understand it, it is due to the dynamic range of the blocked stage (either RF amp or possibly mixer) being exceeded by the strong local signal, meaning that the amplifier spends most of its time either saturated (on positive peaks) or cut off (on negative peaks). It is being switched at the frequency of the qrm signal between those extremes. In the presence of multiple input qrm signals on different frequencies it is likely that the combined instantaneous signal level is always above the amplifier’s saturation level, therefore the amplifier has zero gain. (Vk1da)

[@g3cwi_Radio_Adventures]

@@andrewd4890 Yes. I did wonder about that myself. Also small antennas optimised for gain often have a relatively poor f/b ratio.

[@StreakyP]

I 100% agree with the advantages offered by your filter. Yeas ago I had both a first generation Trio7500 2m FM only rig in the car (which had an internal helical filter) and also a wideband handheld Alinco DJV70 VHF/UHF/Scanning/Airband receive etc etc. The Alinco could do way more than the old Trio, but drive through Glasgow and the Alinco was popping as squawking and farting all the time with breakthrough when the Trio was quiet as the grave. FILTERS CERTAINLY WORK. I'd only suggest a short flexible jumper being used between your filter an the rig rather than the direct coupling shown as the leverage from an accidental sharp tug on the co-ax can easily rip the connector off the top of a modern handheld (especially if it is an SMA connector). If you want a quick and dirty trial of a filter (to confirm the value of buying a professional unit) then a simple co-ax T piece and a shorted quarter wave stub can give some easy practical experience.

[@g3cwi_Radio_Adventures]

Thanks for the feedback and suggestions. However, a quarter-wave co-axial stub will have such a low Q factor that in many cases it will make no discernable difference.

[@Loco_Lui]

I love the opening of this video! The menacing music & tone of voice is great. Desensitization & blocking is certainly a pesky little devil! 👺 & the traveling ham has to be alert for the RF beast at all times or risk his RF being eaten alive.... 😆 Great video. 73 de K5QF

[@g3cwi_Radio_Adventures]

Thanks. I was having a bit of fun. However it’s a very real problem.

[@n1rbd]

When I tried a Baofeng and had this issue, I was actually looking for something like this or possibly fashioning one to try. Wound up getting an FT-270 instead. Glad to see someone brought this to mass market at a reasonable price and compact size!

[@g3cwi_Radio_Adventures]

The FT270 is likely to have good front end filtering.

[@n1rbd]

@@g3cwi_Radio_Adventures I definitely think this was something that was needed in the SOTA space as lots of people with inexpensive starter radios start getting into the hobby.

[@adyg6ad73]

Very informative. Some good practical tips and solutions to this problem. G6AD said that

[@jordesclark]

Very interesting and a useful set of ideas there Richard, thank you. As you say, it can be very difficult to detect desensitization, and it's often more easily blamed on 'dead bands'. 73s

[@g3cwi_Radio_Adventures]

It's really hard to detect sometimes!

[@nojiratzlaff4388]

In my experience, and from all my testing (Agilent 8591A, et al), the only handheld radio make that's filtered enough to appear immune to these effects are made by Motorola.

[@davidvaughn7752]

You are absolutely correct on all points, Richard! I have this problem at my home QTH with my mobile rig that I'm using as my base radio (Alinco DR-735T). I put it on my big 17ft. colinear and it is terrible with desensitization and intermod. I have the same rig in my truck and it happens there too but not as much as the antenna is not as sensitive. Looks like I'll be getting a filter. Your other products work great on my 817-ND and I look forward to seeing the results of the band-pass filter on my Alinco! Question: Can I put it in-line in my mobile rig? Thanks! K7GYB I see from your site that it is rated max 5 watts. Great for handhelds, then! I tend to stay away from summits with transmitters but you are correct that it can be quite a distance away as I experienced a few years back on "Atennuator Hill", here in the Cascades of the PNW, of North America. I still can't figure out where the transmitters were and my radio was acting just like yours was on that day and before I knew what it was. Thanks again for a great video and great products as well. 73

[@g3cwi_Radio_Adventures]

The filter is only rated for 5 Watts so really dsesigned for handies.

[@davidvaughn7752]

@@g3cwi_Radio_Adventures OK, thanks!

[@driverfilmsshortwavechannel]

Whenever Im out Portable I try and avoid somewhere that has these transmitter towers, a bit difficult but we can't have everything. Interesting video, I might invest in one of these in the New Year!

[@g3cwi_Radio_Adventures]

Might actually be worse if they are across the valley!

[@w3les]

WOW NEVER THOUGHT OF THIS!!!!! Thanks

[@g3cwi_Radio_Adventures]

Now you know!

[@CampervanCookout]

Another cracking video Richard

[@g3cwi_Radio_Adventures]

Thanks!

[@TimNair]

Any thoughts as to which HTs have built-in better filtering? I have the Bandpass filter and it's fantastic! I use it frequently and have recommended it to many operators

[@g3cwi_Radio_Adventures]

People suggest that the FT60 is one of the best.

[@moozoowizard]

I wish there was a higher wattage version of the sotabeams 2m bandpass. My F8HP puts out ~6.5 watts. Ideally I want something that handles continuous 10 watts not 2 watts I assume this also reduces spurious emissions?

[@g3cwi_Radio_Adventures]

Yes it will also reduce spurious emissions.

[@MarkPentler]

My Kenwood F7 has two receivers technically and one is more sensitive. Worth mentioning that as well. From my home QTH with a Slim Jim up I get S9 noise on the A receiver (really) and zero on the B receiver. I can’t explain that, but it’s helpful. Why does it drop so much?

[@MarkPentler]

Fantastic video, this. Presumably those masts are VHF band council/transport type stuff?

[@NICKGAR7]

Brilliantly informative. Thanks. I know your SB BPF is relatively QRP rated however can I position it inline between rig (10W) and amp (100-200W)? Thanks, Nick

[@g3cwi_Radio_Adventures]

No unfortunately you can’t

[@alanread6596]

Very interesting

[@g3cwi_Radio_Adventures]

Thanks Alan

[@johnratcliffe6438]

Would a 2m base station also benefit from such a filter?

[@g3cwi_Radio_Adventures]

If you suffer from this type of interference - yes.

[@WHNorthcote]

Is there a power rating for the 2M bandpass filter? If so, then it might solve other interference working from a base station. But good video and informative. Will 2E0WHN

[@g3cwi_Radio_Adventures]

5 Watts - check out the product description!

[@CraigPerry]

This reminds me i still haven’t registered my drone since the law change. Just as well the weather has been too rubbish to fly here!

[@g3cwi_Radio_Adventures]

Mavic Mini here < 250 grams.

[@joeshmoe7899]

Almost as good as Kokotov's helical resonator. www.qsl.net/z33t/baofeng_uv-5r.html

[@g3cwi_Radio_Adventures]

Better in that you dont have to make it!