Commercial Kenwood transceivers for 40 MHz

There are a large number of commercial and utility companies making use of the low VHF band in the USA from 30 to 50 MHz. Several manufacturers including Kenwood sold radios to service this market.

In the past, these were largely operating on FM but many systems are now being replaced with their digital equivalents. As a result, many old Kenwood commercial FM transceivers can be picked up on sites like eBay.

These radios are a potential source of relatively cheap FM radios for the 40 MHz (8-metre) band.

It should be noted that commercial radios are usually programmed to operate on certain frequencies. Any second hand models will need to be re-programmed.

Here are the Kenwood radios that operate on the Low VHF band.

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Kenwood TK-190... This handheld radio comes in two versions. The TK-190K covers 29.7 to 37.0 MHz and the TK-190K2 covers 35.0 to 50.0 MHz. Both versions have an output power of 1-watt (Low) and 6-watts (High).

This radio had a list price of $643 in 2007.

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Kenwood TK-630... This radio was released in the early 90's.

It is available with power output levels of 110 watts on FM! The TK-630 is available in three frequency ranges... 29.7 MHz to 37 MHz, 35 MHz to 43 MHz and 41 MHz to 50 MHz.

Example of BBC TV signal at 45 MHz being heard in South Africa

The BBC recently released this old television clip from 1949 explaining how an amateur radio station in Cape Town, South Africa had received TV signals from the UK.

#OnThisDay 1949: England and South Africa were linked through the magic of radio. pic.twitter.com/BpTODBlaRZ

— BBC Archive (@BBCArchive) October 6, 2019

The map below shows the path which is about 9,700kms or 6,000 miles...

The TV transmitter mentioned in the video was a 405 line transmission from Alexandra Palace in North London. This was vertically polarised with a power of 500 kilowatts (ERP?).

This TV signal had a video carrier on 45.0 MHz and a sound carrier down at 41.5 MHz.

The reception report in 1949 was near the peak of solar cycle 18. As can be seen from the chart below, that was a really good sunspot cycle and conditions were probably excellent on all the HF bands and well up into the low VHF region.

The most likely mode of propagation at 45 MHz was probably multi-hop from the F2 layer in the ionosphere. The maximum usable frequency was probably above 50 MHz so the signals on 45 MHz should have been very good.

It's likely however that with a video signal spread out over three and a half megahertz, the picture was probably very distorted and constantly changing. It should have been possible however to have very good reception of the sound on AM on 41.5 MHz with a dedicated radio receiver.

The radio contact shown in the clip between G8IG in England and ZS1PK in Cape Town, South Africa was probably on 28 MHz AM (note the beam at the start of the clip).

The South African station mentioned that signal were better when things were calm which might infer some sort of tropo ducting. That is unlikely to have been the case as it was very probable that all propagation was via the ionosphere and the weather conditions would have no impact.

All the same, it's an interesting example of early low band VHF TV reception.

US Government Report on 32-42 MHz from 1998

Thanks to Rob, PE9PE who sent on an interesting link recently about a US government report about the low VHF spectrum from 32 to 42 MHz.

After a bit of research, I established that the report titled "NTIA Special Publication 98-36 SPECTRUM REALLOCATION REPORT" was from February 1998.

The report looked at who the existing users were in this part of the spectrum and whether some of the frequencies could be reallocated to commercial interests.

While the full report looked at several different bands, we'll concentrate on the low VHF spectrum here.

I have included sections of interest from the report below with certain key points highlighted in bold.

It might be worth pointing out that antennas for low band VHF tend to be very large compared to those for the higher VHF and UHF bands. For example, a full size quarter wave ground plane antenna is roughly 2.5 metres on 30 MHz and 2 metres on 40 MHz.

While the report is over 20 years old, it does show that even back then there was little commercial interest in the 30 to 50 MHz spectrum.

*****
SECTION 3 ASSESSMENT OF REALLOCATION OPTIONS
INTRODUCTION In the previous section, the bands to be considered for reallocation for non-Federal use were identified. All of the bands being considered for reallocation are used by the Federal Government agencies, in varying degrees, to support Presidential and Congressionally mandated missions. A band-by-band assessment of these factors is presented and recommendations are made as to which bands will be included in the spectrum reallocation plan.32-33, 34-35, 36-37, 38-39, AND 40-42 MHz 

Band Usage 
The Department of Defence (DoD) uses the frequency bands between 32-42 MHz for tactical communication using the Single Channel Ground and Airborne Radio System (SINCGARS) and other land mobile radio (LMR) assets (e.g., Scope Shield II) as well as some non-tactical intra base radio functions.

FCC petitioned to open up 45 to 50 MHz for DRM+ broadcasts in the USA

Currently most of the terrestrial radio stations in the USA broadcast either on the AM band from 540 to 1700 kHz or on the FM band from 88 to 108 MHz. At the end of September 2018, the FCC announced that there were 4,464 stations on AM and 10,867 stations on FM [1].

Due the crowded nature of the existing bands, it has been hard to introduce new digital radio formats.

DRM or Digital Radio Mondiale is a digital format designed to replace existing AM transmissions with clearer audio and with just 20% of the power. DRM+ is the format for VHF.

WRNJ Radio co-owner Larry Tighe has now filed a petition for rulemaking with the FCC, asking that the 45 MHz to 50 MHz band on the VHF spectrum be reallocated for DRM+ transmissions.

In a statement, Tighe said... “The 45–50 MHz band was allocated to two-way radio users in business and government, who have since migrated to higher bandwidths where they can use handsets with smaller antennas. As a result, this spectrum is extremely quiet right now. WRNJ monitored this bandwidth for an extended period of time, and heard very few distant signals.”

“There were 660 TV stations between Channels 2 and 7 before the transition to UHF for HDTV. There are now only approximately 60 TV stations in the USA on those old VHF channels. There is plenty of spectrum to share with a new service, i.e., DRM+ or any modulation, if the FCC really wanted to move AMs.”

Even though the DRM standard has been around for over a decade, it is only recently that it has begun to make serious inroads to the broadcasting scene with India, China and Russia showing an interest. One of the current problems is the high cost of DRM receivers which is prohibitive to consumers in developing countries.

Obviously if the USA opted for a new DRM+ allocation, it would give the format a huge boost. If it turned out to be the 45 to 50 MHz allocation then it raises the possibility of long distance reception by means of Sporadic-E during the summer months or via F2 propagation around the peak of the sunspot cycle.

More info in the links below.

Links...
1) FCC stats for the number of AM and FM stations at the end of Sept 2018
2) https://www.radioworld.com/tech-and-gear/u-s-based-shortwave-broadcasters-eye-digital
3) Previous post - Russia proposes to use DRM on 65.9-74.0 MHz

Low Band VHF Log-Periodic Aerials from Antenna Products Corporation

Thanks to some info from Rob PE9PE, I came across this commercial antenna website in the USA ... https://antennaproducts.com/

Part of their wide range of products includes log-periodic directional antennas for the low VHF band of about 30 to 80 MHz.

The general principle of a log-periodic antenna is that they give a modest amount of gain over a very wide bandwidth as opposed to a typical Yagi which has more gain but only a narrower bandwidth.

While these commercial products are perhaps outside the budget of the typical radio amateur or scanner enthusiast, they do give some idea on the performance to expect from this type of antenna.

Some models...

Model : TLP-20 (pictured above)
Range : 20 MHz - 1000 MHz
Boom Length : 5.1m
Gain : Approx 2 to 6dBd
Link : https://antennaproducts.com/wp-content/uploads/2014/09/TLP-20-1.pdf

Model : LP-102
Range : 30 MHz - 88 MHz
Boom Length : 4.5m
Gain : Approx 5.4 dBd
Link : https://antennaproducts.com/wp-content/uploads/2014/04/LP-102.pdf

Model : TLP-28 
Range : 28 MHz - 100 MHz
Boom Length : 4.1m
Gain : Approx 3dBd
Link : https://antennaproducts.com/wp-content/uploads/2014/04/TLP-28100225.pdf

The website of the company is https://antennaproducts.com/

Commercial Log-Periodic Antenna for 30 to 70 MHz

One of the challenges of listening to Low Band VHF signals is having an antenna that performs well on a wide range of frequencies. One solution is the Log-Periodic antenna.

This 7 element Log-Periodic from M2 Antenna Systems is very much a high product aimed at commercial, scientific and commercial agencies rather than the hobbyist and probably has a price to match. It does however give some insight into that is required to cover the whole spectrum from 30 to 70 MHz.

Some notes and observations...

1) Boom... The boom is 157 inches in length which is about 4 metres.

2) Gain... Even though the Log-Periodic has 7 elements, the gain is very modest at about 4dBd. Note that this is true gain in free space and is honest. They haven't inflated the figures by adding on ground gain to make the antenna look better.

3) Compromise... The modest gain is the price of having a wide band antenna. With a 7 element Yagi, all 7 elements are in use and the gain may be up around 10dbd. With a Log-Periodic, only about 2 to 3 of the 7 elements are active at any particular frequency in the 30-70 MHz range.

4) Phasing harness... Note the phasing harness above the boom which goes back and forth between elements. This is part of the additional complexity of a Log-Periodic as opposed to a Yagi with its parasitic elements.

5) Balun... This antenna has a 4 to 1 Balun at the front and this performs two functions...
a) This is to match a balanced antenna to an unbalanced coax feed
b) It also transforms the 200 Ohm feed impedance of the Log-Periodic down to about 50 Ohms.

More information on the antenna can be found at the following link...

1) 30-70LP7 on M2 Antenna Systems website